Confusion about quality parameters

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Confusion about quality parameters

Ulf Zibis
Hi,

my input is a 1.5 minute mp4 video with 19.5 MB

When I use (with build from dev):
    ./ffmpeg in.mp4 -c:a copy out.mp4
    ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019 the
FFmpeg developers
      built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
in the output lines e.g.
   frame=   51 fps=0.0 q=31.0 size=     256kB time=00:00:02.05
bitrate=1018.9kbits/
I see q=31.0. (the output file is only 5.9 MB)
In the first view this seems to correspond to:
    2 Codec Options
    qmax integer (encoding,video)
        Set max video quantizer scale (VBR). Must be included between -1
and 1024, default value is 31.
But this seems not to be the option to change, to have a better quality.

1. question -> Where in the documentation is stated, which quality is
used by default and how to change it?

When I use (with static release build 4.1.3 from johnvansickle):
    ffmpeg in.mp4 -c:a copy out.mp4
in the output lines e.g.
   frame=   54 fps=0.0 q=28.0 size=       0kB time=00:00:02.20
bitrate=   0.2kbits/
I see q=28.0. (the output file is 16.3 MB)

When using my system's standard version 3.4.6 I get the same q value, so
this seems corresponding to 4.1.3.
Also the visual quality of the output seems similar and has 16.4 MB.
In the heading info (which is missing in the dev build) I also see crf=23.0

2. question -> How does crf correspond to q?

When I use -q 28 (with build from dev):
    ./ffmpeg in.mp4 -q 28 -c:a copy out.mp4
in the output lines e.g.
   frame=   70 fps=0.0 q=28.0 size=       0kB time=00:00:02.84
bitrate=   0.1kbits/
I also see q=28.0, but the output file has only 6.1 MB and really bad
quality, similar to the default with q=31.0

3. question -> What is the reason for this big difference with the same
q=28.0?

Thanks,
-Ulf

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Re: Confusion about quality parameters

Ulf Zibis
Am 25.06.19 um 14:15 schrieb Ulf Zibis:

> Hi,
>
> my input is a 1.5 minute mp4 video with 19.5 MB
>
> When I use (with build from dev):
>     ./ffmpeg in.mp4 -c:a copy out.mp4
>     ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019 the
> FFmpeg developers
>       built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
> in the output lines e.g.
>    frame=   51 fps=0.0 q=31.0 size=     256kB time=00:00:02.05
> bitrate=1018.9kbits/
> I see q=31.0. (the output file is only 5.9 MB)
> In the first view this seems to correspond to:
>     2 Codec Options
>     qmax integer (encoding,video)
>         Set max video quantizer scale (VBR). Must be included between -1
> and 1024, default value is 31.
> But this seems not to be the option to change, to have a better quality.
>
> 1. question -> Where in the documentation is stated, which quality is
> used by default and how to change it?
>
> When I use (with static release build 4.1.3 from johnvansickle):
>     ffmpeg in.mp4 -c:a copy out.mp4
> in the output lines e.g.
>    frame=   54 fps=0.0 q=28.0 size=       0kB time=00:00:02.20
> bitrate=   0.2kbits/
> I see q=28.0. (the output file is 16.3 MB)
>
> When using my system's standard version 3.4.6 I get the same q value, so
> this seems corresponding to 4.1.3.
> Also the visual quality of the output seems similar and has 16.4 MB.
> In the heading info (which is missing in the dev build) I also see crf=23.0
>
> 2. question -> How does crf correspond to q?
>
> When I use -q 28 (with build from dev):
>     ./ffmpeg in.mp4 -q 28 -c:a copy out.mp4
> in the output lines e.g.
>    frame=   70 fps=0.0 q=28.0 size=       0kB time=00:00:02.84
> bitrate=   0.1kbits/
> I also see q=28.0, but the output file has only 6.1 MB and really bad
> quality, similar to the default with q=31.0
>
> 3. question -> What is the reason for this big difference with the same
> q=28.0?


For the reference, here the complete outputs:
================================================
$ ./ffmpeg -i debug/CYD_1.5m_x264.mp4 -c:a copy debug/CYD_1.5m_x264_dev.mp4
ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019 the FFmpeg
developers
  built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
  configuration:
  libavutil      56. 28.100 / 56. 28.100
  libavcodec     58. 52.101 / 58. 52.101
  libavformat    58. 27.103 / 58. 27.103
  libavdevice    58.  7.100 / 58.  7.100
  libavfilter     7. 53.101 /  7. 53.101
  libswscale      5.  4.101 /  5.  4.101
  libswresample   3.  4.100 /  3.  4.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'debug/CYD_1.5m_x264.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:01:30.40, start: 0.000000, bitrate: 1729 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
704x576 [SAR 12:11 DAR 4:3], 1594 kb/s, 25 fps, 25 tbr, 12800 tbn, 50
tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
File 'debug/CYD_1.5m_x264_dev.mp4' already exists. Overwrite ? [y/N] y
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> mpeg4 (native))
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
Output #0, mp4, to 'debug/CYD_1.5m_x264_dev.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.27.103
    Stream #0:0(und): Video: mpeg4 (mp4v / 0x7634706D), yuv420p, 704x576
[SAR 12:11 DAR 4:3], q=2-31, 200 kb/s, 25 fps, 12800 tbn, 25 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.52.101 mpeg4
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
frame=   99 fps=0.0 q=31.0 size=     256kB time=00:00:04.00 bitrate=
524.4kbits/frame=  212 fps=211 q=31.0 size=     512kB time=00:00:08.52
bitrate= 492.2kbits/frame=  324 fps=215 q=31.0 size=     768kB
time=00:00:13.00 bitrate= 483.9kbits/frame=  408 fps=203 q=31.0 size=   
1024kB time=00:00:16.37 bitrate= 512.4kbits/frame=  490 fps=195 q=31.0
size=    1280kB time=00:00:19.65 bitrate= 533.4kbits/frame=  582 fps=193
q=31.0 size=    1536kB time=00:00:23.32 bitrate= 539.4kbits/frame=  658
fps=187 q=31.0 size=    1792kB time=00:00:26.36 bitrate=
556.8kbits/frame=  746 fps=186 q=31.0 size=    2048kB time=00:00:29.88
bitrate= 561.3kbits/frame=  830 fps=184 q=31.0 size=    2304kB
time=00:00:33.25 bitrate= 567.5kbits/frame=  933 fps=186 q=31.0 size=   
2560kB time=00:00:37.37 bitrate= 561.1kbits/frame= 1025 fps=186 q=31.0
size=    2816kB time=00:00:41.04 bitrate= 562.0kbits/frame= 1120 fps=186
q=31.0 size=    3328kB time=00:00:44.84 bitrate= 608.0kbits/frame= 1217
fps=186 q=31.0 size=    3584kB time=00:00:48.73 bitrate=
602.4kbits/frame= 1325 fps=188 q=31.0 size=    3840kB time=00:00:53.04
bitrate= 593.0kbits/frame= 1419 fps=188 q=31.0 size=    3840kB
time=00:00:56.80 bitrate= 553.8kbits/frame= 1512 fps=188 q=31.0 size=   
4096kB time=00:01:00.53 bitrate= 554.3kbits/frame= 1614 fps=189 q=31.0
size=    4352kB time=00:01:04.60 bitrate= 551.8kbits/frame= 1715 fps=190
q=31.0 size=    4608kB time=00:01:08.65 bitrate= 549.9kbits/frame= 1783
fps=187 q=31.0 size=    4864kB time=00:01:11.36 bitrate=
558.4kbits/frame= 1838 fps=183 q=24.8 size=    4864kB time=00:01:13.57
bitrate= 541.5kbits/frame= 1901 fps=180 q=31.0 size=    4864kB
time=00:01:16.09 bitrate= 523.6kbits/frame= 1974 fps=179 q=31.0 size=   
5120kB time=00:01:19.01 bitrate= 530.8kbits/frame= 2080 fps=180 q=31.0
size=    5376kB time=00:01:23.24 bitrate= 529.1kbits/frame= 2181 fps=181
q=31.0 size=    5376kB time=00:01:27.29 bitrate= 504.5kbits/frame= 2260
fps=180 q=31.0 Lsize=    5806kB time=00:01:30.36 bitrate= 526.4kbits/s
speed=7.22x   
video:4341kB audio:1413kB subtitle:0kB other streams:0kB global
headers:0kB muxing overhead: 0.920072%
================================================
$ ffmpeg -i debug/CYD_1.5m_x264.mp4 -c:a copy debug/CYD_1.5m_x264_4.1.mp4
ffmpeg version 4.1.3-static https://johnvansickle.com/ffmpeg/  Copyright
(c) 2000-2019 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --enable-gpl --enable-version3 --enable-static
--disable-debug --disable-ffplay --disable-indev=sndio
--disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r
--enable-gnutls --enable-gmp --enable-gray --enable-libaom
--enable-libfribidi --enable-libass --enable-libvmaf
--enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband
--enable-libsoxr --enable-libspeex --enable-libvorbis --enable-libopus
--enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc
--enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265
--enable-libxml2 --enable-libxvid --enable-libzvbi --enable-libzimg
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'debug/CYD_1.5m_x264.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:01:30.40, start: 0.000000, bitrate: 1729 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
704x576 [SAR 12:11 DAR 4:3], 1594 kb/s, 25 fps, 25 tbr, 12800 tbn, 50
tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
File 'debug/CYD_1.5m_x264_4.1.mp4' already exists. Overwrite ? [y/N] y
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[libx264 @ 0x633c0c0] using SAR=12/11
[libx264 @ 0x633c0c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.1
Cache64
[libx264 @ 0x633c0c0] profile Progressive High, level 3.0, 4:2:0, 8-bit
[libx264 @ 0x633c0c0] 264 - core 157 r2969 d4099dd - H.264/MPEG-4 AVC
codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html -
options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7
psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1
8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=3
lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0
bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250
keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf
mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40
aq=1:1.00
Output #0, mp4, to 'debug/CYD_1.5m_x264_4.1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
    Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661),
yuv420p, 704x576 [SAR 12:11 DAR 4:3], q=-1--1, 25 fps, 12800 tbn, 25 tbc
(default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.35.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
frame=   54 fps=0.0 q=28.0 size=       0kB time=00:00:02.20 bitrate=  
0.2kbits/frame=   67 fps= 63 q=28.0 size=       0kB time=00:00:02.72
bitrate=   0.1kbits/frame=   79 fps= 49 q=28.0 size=       0kB
time=00:00:03.21 bitrate=   0.1kbits/frame=   88 fps= 41 q=28.0
size=     256kB time=00:00:03.57 bitrate= 587.0kbits/frame=  100 fps= 38
q=28.0 size=     256kB time=00:00:04.04 bitrate= 518.8kbits/frame=  112
fps= 35 q=28.0 size=     256kB time=00:00:04.53 bitrate=
462.7kbits/frame=  123 fps= 33 q=28.0 size=     512kB time=00:00:04.96
bitrate= 845.7kbits/frame=  135 fps= 32 q=28.0 size=     512kB
time=00:00:05.45 bitrate= 769.6kbits/frame=  149 fps= 31 q=28.0
size=     512kB time=00:00:06.01 bitrate= 697.3kbits/frame=  161 fps= 30
q=28.0 size=     768kB time=00:00:06.49 bitrate= 968.6kbits/frame=  175
fps= 30 q=28.0 size=     768kB time=00:00:07.05 bitrate=
892.4kbits/frame=  189 fps= 30 q=28.0 size=     768kB time=00:00:07.60
bitrate= 827.3kbits/frame=  202 fps= 29 q=28.0 size=    1024kB
time=00:00:08.13 bitrate=1030.8kbits/frame=  217 fps= 29 q=28.0 size=   
1024kB time=00:00:08.73 bitrate= 960.3kbits/frame=  232 fps= 29 q=28.0
size=    1024kB time=00:00:09.33 bitrate= 898.8kbits/frame=  246 fps= 29
q=28.0 size=    1280kB time=00:00:09.88 bitrate=1060.5kbits/frame=  262
fps= 29 q=28.0 size=    1280kB time=00:00:10.52 bitrate=
996.0kbits/frame=  279 fps= 29 q=28.0 size=    1280kB time=00:00:11.21
bitrate= 935.4kbits/frame=  292 fps= 29 q=28.0 size=    1536kB
time=00:00:11.72 bitrate=1073.4kbits/frame=  307 fps= 29 q=28.0 size=   
1536kB time=00:00:12.32 bitrate=1021.4kbits/frame=  322 fps= 29 q=28.0
size=    1536kB time=00:00:12.93 bitrate= 972.5kbits/frame=  336 fps= 29
q=28.0 size=    1536kB time=00:00:13.49 bitrate= 932.6kbits/frame=  349
fps= 29 q=28.0 size=    1792kB time=00:00:14.00
bitrate=1048.2kbits/frame=  361 fps= 29 q=28.0 size=    1792kB
time=00:00:14.49 bitrate=1012.7kbits/frame=  373 fps= 28 q=28.0 size=   
2048kB time=00:00:14.96 bitrate=1121.1kbits/frame=  385 fps= 28 q=28.0
size=    2048kB time=00:00:15.45 bitrate=1085.5kbits/frame=  397 fps= 28
q=28.0 size=    2048kB time=00:00:15.92 bitrate=1053.5kbits/frame=  410
fps= 28 q=28.0 size=    2304kB time=00:00:16.45
bitrate=1146.8kbits/frame=  422 fps= 28 q=28.0 size=    2304kB
time=00:00:16.92 bitrate=1115.0kbits/frame=  434 fps= 27 q=28.0 size=   
2560kB time=00:00:17.41 bitrate=1204.0kbits/frame=  445 fps= 27 q=28.0
size=    2560kB time=00:00:17.84 bitrate=1175.2kbits/frame=  457 fps= 27
q=28.0 size=    2560kB time=00:00:18.33 bitrate=1143.8kbits/frame=  470
fps= 27 q=28.0 size=    2816kB time=00:00:18.84
bitrate=1224.0kbits/frame=  483 fps= 27 q=28.0 size=    2816kB
time=00:00:19.36 bitrate=1191.6kbits/frame=  496 fps= 27 q=28.0 size=   
2816kB time=00:00:19.89 bitrate=1159.6kbits/frame=  509 fps= 27 q=28.0
size=    3072kB time=00:00:20.40 bitrate=1233.3kbits/frame=  516 fps= 26
q=28.0 size=    3072kB time=00:00:20.68 bitrate=1216.8kbits/frame=  523
fps= 26 q=28.0 size=    3072kB time=00:00:20.96
bitrate=1200.7kbits/frame=  529 fps= 25 q=28.0 size=    3072kB
time=00:00:21.21 bitrate=1186.2kbits/frame=  535 fps= 25 q=28.0 size=   
3072kB time=00:00:21.45 bitrate=1173.2kbits/frame=  546 fps= 25 q=28.0
size=    3328kB time=00:00:21.89 bitrate=1245.0kbits/frame=  559 fps= 25
q=28.0 size=    3328kB time=00:00:22.41 bitrate=1216.5kbits/frame=  571
fps= 25 q=28.0 size=    3328kB time=00:00:22.88
bitrate=1191.6kbits/frame=  585 fps= 25 q=28.0 size=    3584kB
time=00:00:23.44 bitrate=1252.3kbits/frame=  599 fps= 25 q=28.0 size=   
3584kB time=00:00:24.01 bitrate=1222.8kbits/frame=  613 fps= 25 q=28.0
size=    3840kB time=00:00:24.57 bitrate=1280.0kbits/frame=  625 fps= 25
q=28.0 size=    3840kB time=00:00:25.04 bitrate=1256.0kbits/frame=  638
fps= 25 q=28.0 size=    3840kB time=00:00:25.57
bitrate=1229.8kbits/frame=  646 fps= 25 q=28.0 size=    4096kB
time=00:00:25.89 bitrate=1295.6kbits/frame=  657 fps= 25 q=28.0 size=   
4096kB time=00:00:26.32 bitrate=1274.6kbits/frame=  671 fps= 25 q=28.0
size=    4352kB time=00:00:26.88 bitrate=1326.3kbits/frame=  685 fps= 25
q=28.0 size=    4352kB time=00:00:27.45 bitrate=1298.5kbits/frame=  694
fps= 25 q=28.0 size=    4352kB time=00:00:27.81
bitrate=1281.6kbits/frame=  706 fps= 25 q=28.0 size=    4608kB
time=00:00:28.28 bitrate=1334.5kbits/frame=  715 fps= 24 q=28.0 size=   
4608kB time=00:00:28.65 bitrate=1317.6kbits/frame=  725 fps= 24 q=28.0
size=    4608kB time=00:00:29.05 bitrate=1299.2kbits/frame=  737 fps= 24
q=28.0 size=    4864kB time=00:00:29.52 bitrate=1349.6kbits/frame=  749
fps= 24 q=28.0 size=    4864kB time=00:00:30.01
bitrate=1327.5kbits/frame=  756 fps= 24 q=28.0 size=    4864kB
time=00:00:30.29 bitrate=1315.3kbits/frame=  764 fps= 24 q=28.0 size=   
4864kB time=00:00:30.61 bitrate=1301.6kbits/frame=  771 fps= 24 q=28.0
size=    5120kB time=00:00:30.89 bitrate=1357.8kbits/frame=  779 fps= 24
q=28.0 size=    5120kB time=00:00:31.21 bitrate=1343.9kbits/frame=  789
fps= 24 q=28.0 size=    5120kB time=00:00:31.61
bitrate=1326.7kbits/frame=  800 fps= 24 q=28.0 size=    5376kB
time=00:00:32.04 bitrate=1374.4kbits/frame=  811 fps= 24 q=28.0 size=   
5376kB time=00:00:32.49 bitrate=1355.5kbits/frame=  824 fps= 24 q=25.0
size=    5376kB time=00:00:33.00 bitrate=1334.5kbits/frame=  838 fps= 24
q=28.0 size=    5632kB time=00:00:33.57 bitrate=1374.0kbits/frame=  845
fps= 23 q=28.0 size=    5632kB time=00:00:33.85
bitrate=1362.8kbits/frame=  855 fps= 23 q=28.0 size=    5632kB
time=00:00:34.24 bitrate=1347.5kbits/frame=  863 fps= 23 q=28.0 size=   
5632kB time=00:00:34.56 bitrate=1335.0kbits/frame=  870 fps= 23 q=28.0
size=    5888kB time=00:00:34.85 bitrate=1383.7kbits/frame=  877 fps= 23
q=28.0 size=    5888kB time=00:00:35.13 bitrate=1372.8kbits/frame=  886
fps= 23 q=28.0 size=    5888kB time=00:00:35.49
bitrate=1358.8kbits/frame=  891 fps= 23 q=28.0 size=    5888kB
time=00:00:35.69 bitrate=1351.5kbits/frame=  898 fps= 22 q=28.0 size=   
6144kB time=00:00:35.96 bitrate=1399.4kbits/frame=  905 fps= 22 q=28.0
size=    6144kB time=00:00:36.24 bitrate=1388.6kbits/frame=  911 fps= 22
q=28.0 size=    6144kB time=00:00:36.48 bitrate=1379.7kbits/frame=  917
fps= 22 q=28.0 size=    6144kB time=00:00:36.73
bitrate=1370.1kbits/frame=  923 fps= 22 q=28.0 size=    6144kB
time=00:00:36.97 bitrate=1361.4kbits/frame=  934 fps= 22 q=28.0 size=   
6400kB time=00:00:37.41 bitrate=1401.2kbits/frame=  943 fps= 22 q=28.0
size=    6400kB time=00:00:37.76 bitrate=1388.5kbits/frame=  952 fps= 22
q=28.0 size=    6400kB time=00:00:38.12 bitrate=1375.3kbits/frame=  960
fps= 22 q=28.0 size=    6400kB time=00:00:38.44
bitrate=1363.8kbits/frame=  969 fps= 22 q=28.0 size=    6656kB
time=00:00:38.80 bitrate=1405.1kbits/frame=  982 fps= 22 q=28.0 size=   
6656kB time=00:00:39.33 bitrate=1386.1kbits/frame=  995 fps= 22 q=28.0
size=    6656kB time=00:00:39.85 bitrate=1368.3kbits/frame= 1008 fps= 22
q=28.0 size=    6912kB time=00:00:40.36 bitrate=1402.9kbits/frame= 1021
fps= 22 q=28.0 size=    6912kB time=00:00:40.89
bitrate=1384.6kbits/frame= 1034 fps= 22 q=28.0 size=    7168kB
time=00:00:41.40 bitrate=1418.1kbits/frame= 1048 fps= 22 q=28.0 size=   
7168kB time=00:00:41.96 bitrate=1399.4kbits/frame= 1062 fps= 22 q=28.0
size=    7168kB time=00:00:42.53 bitrate=1380.4kbits/frame= 1073 fps= 22
q=28.0 size=    7424kB time=00:00:42.96 bitrate=1415.5kbits/frame= 1087
fps= 22 q=28.0 size=    7424kB time=00:00:43.52
bitrate=1397.5kbits/frame= 1101 fps= 22 q=28.0 size=    7680kB
time=00:00:44.09 bitrate=1426.8kbits/frame= 1115 fps= 22 q=28.0 size=   
7680kB time=00:00:44.65 bitrate=1409.0kbits/frame= 1129 fps= 22 q=28.0
size=    7936kB time=00:00:45.21 bitrate=1437.8kbits/frame= 1142 fps= 22
q=28.0 size=    7936kB time=00:00:45.72 bitrate=1421.7kbits/frame= 1155
fps= 22 q=28.0 size=    8192kB time=00:00:46.24
bitrate=1451.3kbits/frame= 1169 fps= 22 q=28.0 size=    8192kB
time=00:00:46.81 bitrate=1433.5kbits/frame= 1181 fps= 22 q=28.0 size=   
8192kB time=00:00:47.28 bitrate=1419.2kbits/frame= 1191 fps= 22 q=28.0
size=    8448kB time=00:00:47.69 bitrate=1451.2kbits/frame= 1201 fps= 22
q=28.0 size=    8448kB time=00:00:48.09 bitrate=1438.9kbits/frame= 1212
fps= 22 q=28.0 size=    8704kB time=00:00:48.52
bitrate=1469.5kbits/frame= 1222 fps= 22 q=28.0 size=    8704kB
time=00:00:48.92 bitrate=1457.3kbits/frame= 1232 fps= 22 q=28.0 size=   
8704kB time=00:00:49.33 bitrate=1445.3kbits/frame= 1243 fps= 22 q=28.0
size=    8960kB time=00:00:49.76 bitrate=1475.1kbits/frame= 1256 fps= 22
q=28.0 size=    8960kB time=00:00:50.29 bitrate=1459.5kbits/frame= 1271
fps= 22 q=28.0 size=    9216kB time=00:00:50.89
bitrate=1483.5kbits/frame= 1283 fps= 22 q=28.0 size=    9216kB
time=00:00:51.36 bitrate=1470.0kbits/frame= 1297 fps= 22 q=28.0 size=   
9216kB time=00:00:51.93 bitrate=1453.7kbits/frame= 1310 fps= 22 q=28.0
size=    9472kB time=00:00:52.44 bitrate=1479.5kbits/frame= 1320 fps= 22
q=28.0 size=    9472kB time=00:00:52.85 bitrate=1468.1kbits/frame= 1335
fps= 22 q=28.0 size=    9472kB time=00:00:53.45
bitrate=1451.7kbits/frame= 1347 fps= 22 q=28.0 size=    9728kB
time=00:00:53.92 bitrate=1478.0kbits/frame= 1361 fps= 22 q=28.0 size=   
9728kB time=00:00:54.49 bitrate=1462.3kbits/frame= 1376 fps= 22 q=28.0
size=    9728kB time=00:00:55.09 bitrate=1446.5kbits/frame= 1391 fps= 22
q=28.0 size=    9984kB time=00:00:55.69 bitrate=1468.6kbits/frame= 1406
fps= 22 q=28.0 size=    9984kB time=00:00:56.28
bitrate=1453.1kbits/frame= 1420 fps= 22 q=28.0 size=   10240kB
time=00:00:56.84 bitrate=1475.8kbits/frame= 1436 fps= 22 q=28.0 size=  
10240kB time=00:00:57.48 bitrate=1459.3kbits/frame= 1451 fps= 23 q=28.0
size=   10496kB time=00:00:58.09 bitrate=1480.2kbits/frame= 1466 fps= 23
q=28.0 size=   10496kB time=00:00:58.69 bitrate=1464.8kbits/frame= 1477
fps= 23 q=28.0 size=   10496kB time=00:00:59.12
bitrate=1454.3kbits/frame= 1490 fps= 23 q=28.0 size=   10752kB
time=00:00:59.65 bitrate=1476.4kbits/frame= 1504 fps= 23 q=28.0 size=  
10752kB time=00:01:00.21 bitrate=1462.8kbits/frame= 1518 fps= 23 q=28.0
size=   11008kB time=00:01:00.76 bitrate=1484.0kbits/frame= 1532 fps= 23
q=28.0 size=   11008kB time=00:01:01.32 bitrate=1470.5kbits/frame= 1546
fps= 23 q=28.0 size=   11264kB time=00:01:01.89
bitrate=1490.7kbits/frame= 1560 fps= 23 q=28.0 size=   11264kB
time=00:01:02.45 bitrate=1477.5kbits/frame= 1574 fps= 23 q=28.0 size=  
11264kB time=00:01:03.00 bitrate=1464.5kbits/frame= 1588 fps= 23 q=28.0
size=   11520kB time=00:01:03.56 bitrate=1484.7kbits/frame= 1602 fps= 23
q=28.0 size=   11520kB time=00:01:04.13 bitrate=1471.4kbits/frame= 1617
fps= 23 q=28.0 size=   11776kB time=00:01:04.73
bitrate=1490.2kbits/frame= 1630 fps= 23 q=28.0 size=   11776kB
time=00:01:05.24 bitrate=1478.5kbits/frame= 1645 fps= 23 q=28.0 size=  
12032kB time=00:01:05.84 bitrate=1496.9kbits/frame= 1658 fps= 23 q=28.0
size=   12032kB time=00:01:06.37 bitrate=1484.9kbits/frame= 1671 fps= 23
q=28.0 size=   12032kB time=00:01:06.88 bitrate=1473.8kbits/frame= 1686
fps= 23 q=28.0 size=   12288kB time=00:01:07.49
bitrate=1491.3kbits/frame= 1700 fps= 23 q=28.0 size=   12288kB
time=00:01:08.05 bitrate=1479.2kbits/frame= 1714 fps= 23 q=28.0 size=  
12544kB time=00:01:08.60 bitrate=1497.8kbits/frame= 1728 fps= 23 q=28.0
size=   12544kB time=00:01:09.16 bitrate=1485.8kbits/frame= 1740 fps= 23
q=28.0 size=   12800kB time=00:01:09.65 bitrate=1505.4kbits/frame= 1750
fps= 23 q=28.0 size=   12800kB time=00:01:10.05
bitrate=1496.7kbits/frame= 1758 fps= 23 q=28.0 size=   12800kB
time=00:01:10.37 bitrate=1489.9kbits/frame= 1768 fps= 23 q=28.0 size=  
13056kB time=00:01:10.76 bitrate=1511.5kbits/frame= 1780 fps= 23 q=28.0
size=   13056kB time=00:01:11.25 bitrate=1501.1kbits/frame= 1795 fps= 23
q=28.0 size=   13312kB time=00:01:11.85 bitrate=1517.8kbits/frame= 1807
fps= 23 q=28.0 size=   13312kB time=00:01:12.32
bitrate=1507.9kbits/frame= 1820 fps= 23 q=28.0 size=   13312kB
time=00:01:12.85 bitrate=1496.9kbits/frame= 1833 fps= 23 q=28.0 size=  
13568kB time=00:01:13.36 bitrate=1515.0kbits/frame= 1847 fps= 23 q=28.0
size=   13568kB time=00:01:13.92 bitrate=1503.6kbits/frame= 1860 fps= 23
q=28.0 size=   13824kB time=00:01:14.45 bitrate=1521.0kbits/frame= 1872
fps= 23 q=28.0 size=   13824kB time=00:01:14.92
bitrate=1511.5kbits/frame= 1886 fps= 23 q=28.0 size=   13824kB
time=00:01:15.49 bitrate=1500.0kbits/frame= 1900 fps= 23 q=28.0 size=  
14080kB time=00:01:16.05 bitrate=1516.6kbits/frame= 1915 fps= 23 q=28.0
size=   14080kB time=00:01:16.65 bitrate=1504.8kbits/frame= 1928 fps= 23
q=28.0 size=   14336kB time=00:01:17.16 bitrate=1522.0kbits/frame= 1942
fps= 23 q=28.0 size=   14336kB time=00:01:17.73
bitrate=1510.7kbits/frame= 1958 fps= 23 q=28.0 size=   14336kB
time=00:01:18.37 bitrate=1498.4kbits/frame= 1974 fps= 23 q=28.0 size=  
14592kB time=00:01:19.01 bitrate=1512.8kbits/frame= 1995 fps= 23 q=28.0
size=   14592kB time=00:01:19.85 bitrate=1497.0kbits/frame= 2015 fps= 23
q=28.0 size=   14592kB time=00:01:20.64 bitrate=1482.4kbits/frame= 2034
fps= 24 q=28.0 size=   14848kB time=00:01:21.40
bitrate=1494.1kbits/frame= 2053 fps= 24 q=28.0 size=   14848kB
time=00:01:22.17 bitrate=1480.2kbits/frame= 2071 fps= 24 q=28.0 size=  
14848kB time=00:01:22.88 bitrate=1467.6kbits/frame= 2088 fps= 24 q=28.0
size=   14848kB time=00:01:23.56 bitrate=1455.6kbits/frame= 2100 fps= 24
q=28.0 size=   14848kB time=00:01:24.05 bitrate=1447.1kbits/frame= 2113
fps= 24 q=28.0 size=   14848kB time=00:01:24.56
bitrate=1438.4kbits/frame= 2129 fps= 24 q=28.0 size=   15104kB
time=00:01:25.20 bitrate=1452.2kbits/frame= 2145 fps= 24 q=28.0 size=  
15104kB time=00:01:25.84 bitrate=1441.3kbits/frame= 2161 fps= 24 q=28.0
size=   15104kB time=00:01:26.48 bitrate=1430.7kbits/frame= 2169 fps= 24
q=28.0 size=   15104kB time=00:01:26.80 bitrate=1425.4kbits/frame= 2177
fps= 24 q=28.0 size=   15104kB time=00:01:27.12
bitrate=1420.2kbits/frame= 2186 fps= 24 q=28.0 size=   15104kB
time=00:01:27.48 bitrate=1414.3kbits/frame= 2195 fps= 24 q=28.0 size=  
15360kB time=00:01:27.85 bitrate=1432.3kbits/frame= 2207 fps= 24 q=28.0
size=   15360kB time=00:01:28.32 bitrate=1424.7kbits/frame= 2225 fps= 24
q=28.0 size=   15360kB time=00:01:29.04 bitrate=1413.1kbits/frame= 2242
fps= 24 q=28.0 size=   15360kB time=00:01:29.73
bitrate=1402.2kbits/frame= 2253 fps= 24 q=28.0 size=   15360kB
time=00:01:29.99 bitrate=1398.2kbits/frame= 2260 fps= 23 q=-1.0 Lsize=  
15916kB time=00:01:30.28 bitrate=1444.3kbits/s speed=0.937x   
video:14434kB audio:1413kB subtitle:0kB other streams:0kB global
headers:0kB muxing overhead: 0.440433%
[libx264 @ 0x633c0c0] frame I:12    Avg QP:20.71  size: 38215
[libx264 @ 0x633c0c0] frame P:605   Avg QP:23.49  size: 13591
[libx264 @ 0x633c0c0] frame B:1643  Avg QP:27.30  size:  3712
[libx264 @ 0x633c0c0] consecutive B-frames:  1.0%  5.9%  1.1% 92.0%
[libx264 @ 0x633c0c0] mb I  I16..4:  7.1% 84.3%  8.6%
[libx264 @ 0x633c0c0] mb P  I16..4:  1.7%  7.7%  1.1%  P16..4: 47.1%
21.1% 10.0%  0.0%  0.0%    skip:11.3%
[libx264 @ 0x633c0c0] mb B  I16..4:  0.1%  0.6%  0.1%  B16..8: 50.5% 
6.7%  1.2%  direct: 2.3%  skip:38.4%  L0:43.4% L1:48.4% BI: 8.2%
[libx264 @ 0x633c0c0] 8x8 transform intra:74.8% inter:78.5%
[libx264 @ 0x633c0c0] coded y,uvDC,uvAC intra: 64.7% 55.6% 6.8% inter:
21.5% 14.0% 0.2%
[libx264 @ 0x633c0c0] i16 v,h,dc,p: 33% 36% 11% 20%
[libx264 @ 0x633c0c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 16% 22%  5% 
6%  8%  7%  7%  7%
[libx264 @ 0x633c0c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 27% 16%  5% 
8%  7%  8%  6%  6%
[libx264 @ 0x633c0c0] i8c dc,h,v,p: 56% 19% 19%  6%
[libx264 @ 0x633c0c0] Weighted P-Frames: Y:8.3% UV:1.5%
[libx264 @ 0x633c0c0] ref P L0: 50.6% 15.2% 24.8%  8.8%  0.6%
[libx264 @ 0x633c0c0] ref B L0: 86.2% 11.6%  2.2%
[libx264 @ 0x633c0c0] ref B L1: 96.4%  3.6%
[libx264 @ 0x633c0c0] kb/s:1307.93
================================================
$ ./ffmpeg -i debug/CYD_1.5m_x264.mp4 -q 28 -c:a copy
debug/CYD_1.5m_x264_dev_q28.mp4
ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019 the FFmpeg
developers
  built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
  configuration:
  libavutil      56. 28.100 / 56. 28.100
  libavcodec     58. 52.101 / 58. 52.101
  libavformat    58. 27.103 / 58. 27.103
  libavdevice    58.  7.100 / 58.  7.100
  libavfilter     7. 53.101 /  7. 53.101
  libswscale      5.  4.101 /  5.  4.101
  libswresample   3.  4.100 /  3.  4.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'debug/CYD_1.5m_x264.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:01:30.40, start: 0.000000, bitrate: 1729 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
704x576 [SAR 12:11 DAR 4:3], 1594 kb/s, 25 fps, 25 tbr, 12800 tbn, 50
tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> mpeg4 (native))
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
Output #0, mp4, to 'debug/CYD_1.5m_x264_dev_q28.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.27.103
    Stream #0:0(und): Video: mpeg4 (mp4v / 0x7634706D), yuv420p, 704x576
[SAR 12:11 DAR 4:3], q=2-31, 200 kb/s, 25 fps, 12800 tbn, 25 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.52.101 mpeg4
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
frame=   70 fps=0.0 q=28.0 size=       0kB time=00:00:02.84 bitrate=  
0.1kbits/frame=  179 fps=178 q=28.0 size=     512kB time=00:00:07.20
bitrate= 582.6kbits/frame=  301 fps=199 q=28.0 size=     768kB
time=00:00:12.08 bitrate= 520.6kbits/frame=  381 fps=189 q=28.0 size=   
1024kB time=00:00:15.28 bitrate= 548.8kbits/frame=  471 fps=187 q=28.0
size=    1280kB time=00:00:18.89 bitrate= 555.1kbits/frame=  569 fps=188
q=28.0 size=    1536kB time=00:00:22.81 bitrate= 551.5kbits/frame=  662
fps=188 q=28.0 size=    1792kB time=00:00:26.53 bitrate=
553.2kbits/frame=  741 fps=184 q=28.0 size=    2048kB time=00:00:29.69
bitrate= 565.0kbits/frame=  828 fps=183 q=28.0 size=    2304kB
time=00:00:33.17 bitrate= 569.0kbits/frame=  925 fps=184 q=28.0 size=   
2816kB time=00:00:37.05 bitrate= 622.5kbits/frame= 1010 fps=183 q=28.0
size=    3072kB time=00:00:40.44 bitrate= 622.2kbits/frame= 1101 fps=182
q=28.0 size=    3328kB time=00:00:44.09 bitrate= 618.3kbits/frame= 1197
fps=183 q=28.0 size=    3584kB time=00:00:47.92 bitrate=
612.6kbits/frame= 1300 fps=185 q=28.0 size=    3840kB time=00:00:52.04
bitrate= 604.5kbits/frame= 1407 fps=187 q=28.0 size=    4096kB
time=00:00:56.33 bitrate= 595.7kbits/frame= 1504 fps=187 q=28.0 size=   
4096kB time=00:01:00.21 bitrate= 557.3kbits/frame= 1607 fps=188 q=28.0
size=    4352kB time=00:01:04.33 bitrate= 554.2kbits/frame= 1703 fps=188
q=28.0 size=    4608kB time=00:01:08.16 bitrate= 553.8kbits/frame= 1802
fps=188 q=28.0 size=    4864kB time=00:01:12.12 bitrate=
552.4kbits/frame= 1904 fps=189 q=28.0 size=    5120kB time=00:01:16.20
bitrate= 550.4kbits/frame= 2032 fps=192 q=28.0 size=    5376kB
time=00:01:21.32 bitrate= 541.6kbits/frame= 2125 fps=192 q=28.0 size=   
5376kB time=00:01:25.05 bitrate= 517.8kbits/frame= 2236 fps=193 q=28.0
size=    5632kB time=00:01:29.49 bitrate= 515.5kbits/frame= 2260 fps=193
q=28.0 Lsize=    5939kB time=00:01:30.36 bitrate= 538.4kbits/s
speed=7.73x   
video:4473kB audio:1413kB subtitle:0kB other streams:0kB global
headers:0kB muxing overhead: 0.899318%

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Re: Confusion about quality parameters

Carl Eugen Hoyos-2
In reply to this post by Ulf Zibis
Am Di., 25. Juni 2019 um 14:15 Uhr schrieb Ulf Zibis <[hidden email]>:

> my input is a 1.5 minute mp4 video with 19.5 MB
>
> When I use (with build from dev):
>     ./ffmpeg in.mp4 -c:a copy out.mp4

You do not specify an encoder here, mp4 defaults to x264.

>     ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019
> the FFmpeg developers
>       built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
> in the output lines e.g.
>    frame=   51 fps=0.0 q=31.0 size=     256kB time=00:00:02.05
> bitrate=1018.9kbits/
> I see q=31.0. (the output file is only 5.9 MB)
> In the first view this seems to correspond to:
>     2 Codec Options

>     qmax integer (encoding,video)
>         Set max video quantizer scale (VBR). Must be included
> between -1 and 1024, default value is 31.

This option only applies to (some) internal encoders, not x264.

Carl Eugen
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Re: Confusion about quality parameters

Moritz Barsnick
In reply to this post by Ulf Zibis
On Tue, Jun 25, 2019 at 14:48:58 +0200, Ulf Zibis wrote:
> > my input is a 1.5 minute mp4 video with 19.5 MB
[...]
> >     ./ffmpeg in.mp4 -c:a copy out.mp4
> >     ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019 the
[...]
> > I see q=31.0. (the output file is only 5.9 MB)
[...]
> > When I use (with static release build 4.1.3 from johnvansickle):
> >     ffmpeg in.mp4 -c:a copy out.mp4
[...]
> > I see q=28.0. (the output file is 16.3 MB)

The reason for the size difference is pretty obvious, if you actually
look at the *complete* output. (Which, again - for everyone - is the
reason we request to see it. ;-))

> $ ./ffmpeg -i debug/CYD_1.5m_x264.mp4 -c:a copy debug/CYD_1.5m_x264_dev.mp4
> ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019 the FFmpeg developers
[...]
> Output #0, mp4, to 'debug/CYD_1.5m_x264_dev.mp4':
>   Metadata:
>     major_brand     : isom
>     minor_version   : 512
>     compatible_brands: isomiso2avc1mp41
>     encoder         : Lavf58.27.103
>     Stream #0:0(und): Video: mpeg4 (mp4v / 0x7634706D), yuv420p, 704x576 [SAR 12:11 DAR 4:3], q=2-31, 200 kb/s, 25 fps, 12800 tbn, 25 tbc (default)

> $ ffmpeg -i debug/CYD_1.5m_x264.mp4 -c:a copy debug/CYD_1.5m_x264_4.1.mp4
> ffmpeg version 4.1.3-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
[...]
> Output #0, mp4, to 'debug/CYD_1.5m_x264_4.1.mp4':
>   Metadata:
>     major_brand     : isom
>     minor_version   : 512
>     compatible_brands: isomiso2avc1mp41
>     encoder         : Lavf58.20.100
>     Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 704x576 [SAR 12:11 DAR 4:3], q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)

Your self-compiled binary does not include support for libx264,
therefore the output format mp4 defaults to the mpeg4 video codec. This
behaves totally differently to libx264, therefore the sizes (and
default quality settings, and more perhaps) differ.

Otherwise, regarding "-crf" vs "-q" (and everything else): Please see
what Carl Eugen wrote.

Cheers,
Moritz
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Re: Confusion about quality parameters

Gyan
In reply to this post by Carl Eugen Hoyos-2


On 25-06-2019 06:34 PM, Carl Eugen Hoyos wrote:
>>      qmax integer (encoding,video)
>>          Set max video quantizer scale (VBR). Must be included
>> between -1 and 1024, default value is 31.
> This option only applies to (some) internal encoders, not x264.
The libx264 wrapper does look at and convey avctx->qmax (and qmin).

Gyan
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Re: Confusion about quality parameters

Ulf Zibis
In reply to this post by Moritz Barsnick

Am 25.06.19 um 15:23 schrieb Moritz Barsnick:
> The reason for the size difference is pretty obvious, if you actually
Not to me. With setting q the same value for both builds, i.e. 28.0, the
size and the visual quality is *much different*, even from honoring the
complete output and even libx264 vs. mpeg4.

Question 4.) So why is the default of the dev build set to such bad
quality and why are the q factors such incoherent?

> look at the *complete* output.
>
> (Which, again - for everyone - is the
> reason we request to see it. ;-))
Obviously you didn't view my post to the end. There it is.

> Your self-compiled binary does not include support for libx264,
> therefore the output format mp4 defaults to the mpeg4 video codec. This
> behaves totally differently to libx264, therefore the sizes (and
> default quality settings, and more perhaps) differ.

This is what I really didn't strike. Thanks for the hint. But I think,
it doesn't answer the above question.


> Otherwise, regarding "-crf" vs "-q" (and everything else): Please see
> what Carl Eugen wrote.

Sorry, I don't see any answer on this in Carl Eugens post.

Please have a thought on my question 1.)
Where in the documentation I find, which quality is used by default and
how to change it?
In other words, wouldn't it make sense to add this, if this information
is missing?

Regards
-Ulf

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Re: Confusion about quality parameters

Ulf Zibis
In reply to this post by Carl Eugen Hoyos-2

Am 25.06.19 um 15:04 schrieb Carl Eugen Hoyos:
> Am Di., 25. Juni 2019 um 14:15 Uhr schrieb Ulf Zibis <[hidden email]>:
>
>> my input is a 1.5 minute mp4 video with 19.5 MB
>>
>> When I use (with build from dev):
>>     ./ffmpeg in.mp4 -c:a copy out.mp4
> You do not specify an encoder here, mp4 defaults to x264.

If I understand Moritz and my output correct, it's quite contrary: the
dev build defaults to mpeg4.

-Ulf
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Re: Confusion about quality parameters

Carl Eugen Hoyos-2
Am Di., 25. Juni 2019 um 20:11 Uhr schrieb Ulf Zibis <[hidden email]>:

>
> Am 25.06.19 um 15:04 schrieb Carl Eugen Hoyos:
> > Am Di., 25. Juni 2019 um 14:15 Uhr schrieb Ulf Zibis <[hidden email]>:
> >
> >> my input is a 1.5 minute mp4 video with 19.5 MB
> >>
> >> When I use (with build from dev):
> >>     ./ffmpeg in.mp4 -c:a copy out.mp4
> > You do not specify an encoder here, mp4 defaults to x264.
>
> If I understand Moritz and my output correct, it's quite contrary:
> the dev build defaults to mpeg4.

In this case (your forgot to provide the complete, uncut console
output, so I had to guess) you have to provide either a constant
quantiser or a bitrate for the command line to produce useful
output (assuming state-of-the-art input as opposed to very low-res
video).

Carl Eugen
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Re: Confusion about quality parameters

Carl Eugen Hoyos-2
In reply to this post by Ulf Zibis
Am Di., 25. Juni 2019 um 20:07 Uhr schrieb Ulf Zibis <[hidden email]>:

> Question 4.) So why is the default of the dev build set to such bad
> quality and why are the q factors such incoherent?

It is not "set to such bad quality" but your command line didn't make
sense.

Carl Eugen
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Re: Confusion about quality parameters

Ulf Zibis
In reply to this post by Carl Eugen Hoyos-2

Am 25.06.19 um 20:16 schrieb Carl Eugen Hoyos:

> Am Di., 25. Juni 2019 um 20:11 Uhr schrieb Ulf Zibis <[hidden email]>:
>> Am 25.06.19 um 15:04 schrieb Carl Eugen Hoyos:
>>> Am Di., 25. Juni 2019 um 14:15 Uhr schrieb Ulf Zibis <[hidden email]>:
>>>
>>>> my input is a 1.5 minute mp4 video with 19.5 MB
>>>>
>>>> When I use (with build from dev):
>>>>     ./ffmpeg in.mp4 -c:a copy out.mp4
>>> You do not specify an encoder here, mp4 defaults to x264.
>> If I understand Moritz and my output correct, it's quite contrary:
>> the dev build defaults to mpeg4.
> In this case (your forgot to provide the complete, uncut console
> output, so I had to guess) you have to provide either a constant
> quantiser or a bitrate for the command line to produce useful
> output (assuming state-of-the-art input as opposed to very low-res
> video).

Do you want to say, that ffmpeg by default always markably decreases the
bit rate and with that the quality, so a high res video is transcoded to
a low res video and a low res to a very very low res one?

Btw, sorry that I assumed you know what I meant with "build from dev".
But anyway I had post-posted the *complete* console output some minutes
later, Didn't you receive it?

-Ulf

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Re: Confusion about quality parameters

Ulf Zibis
In reply to this post by Carl Eugen Hoyos-2

Am 25.06.19 um 20:18 schrieb Carl Eugen Hoyos:
> Am Di., 25. Juni 2019 um 20:07 Uhr schrieb Ulf Zibis <[hidden email]>:
>
>> Question 4.) So why is the default of the dev build set to such bad
>> quality and why are the q factors such incoherent?
> It is not "set to such bad quality" but your command line didn't make
> sense.
I originally started with:

./ffmpeg -i in.mp4 -vf some-filter -c:a copy out.mp4

This resulted in a very bad quality with a quarter of filesize of the
original, so to exclude the filter for causing this I used the
"non-sense' command line for test.

-Ulf
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Re: Confusion about quality parameters

Carl Eugen Hoyos-2
In reply to this post by Ulf Zibis
Am Di., 25. Juni 2019 um 20:32 Uhr schrieb Ulf Zibis <[hidden email]>:

>
> Am 25.06.19 um 20:16 schrieb Carl Eugen Hoyos:
> > Am Di., 25. Juni 2019 um 20:11 Uhr schrieb Ulf Zibis <[hidden email]>:
> >> Am 25.06.19 um 15:04 schrieb Carl Eugen Hoyos:
> >>> Am Di., 25. Juni 2019 um 14:15 Uhr schrieb Ulf Zibis <[hidden email]>:
> >>>
> >>>> my input is a 1.5 minute mp4 video with 19.5 MB
> >>>>
> >>>> When I use (with build from dev):
> >>>>     ./ffmpeg in.mp4 -c:a copy out.mp4
> >>> You do not specify an encoder here, mp4 defaults to x264.
> >> If I understand Moritz and my output correct, it's quite contrary:
> >> the dev build defaults to mpeg4.
> > In this case (your forgot to provide the complete, uncut console
> > output, so I had to guess) you have to provide either a constant
> > quantiser or a bitrate for the command line to produce useful
> > output (assuming state-of-the-art input as opposed to very low-res
> > video).
>
> Do you want to say, that ffmpeg by default always markably decreases the
> bit rate and with that the quality, so a high res video is transcoded to
> a low res video and a low res to a very very low res one?

Definitely not.

The default bitrate may be too low for your requirements though.
(Please avoid sending a patch.)

> Btw, sorry that I assumed you know what I meant with "build from dev".
> But anyway I had post-posted the *complete* console output some minutes
> later,

Separating the command line from the console output is a safe
way to ensure its content is missed (qed).

Carl Eugen
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Re: Confusion about quality parameters

Moritz Barsnick
In reply to this post by Ulf Zibis
On Tue, Jun 25, 2019 at 20:01:49 +0200, Ulf Zibis wrote:
>
> Question 4.) So why is the default of the dev build set to such bad
> quality and why are the q factors such incoherent?

This has nothing to do with the dev branch, only with your particular
build. It uses different codecs, and these behave totally differently -
both by nature, and by default settings.

> > behaves totally differently to libx264, therefore the sizes (and
> > default quality settings, and more perhaps) differ.
>
> This is what I really didn't strike. Thanks for the hint. But I think,
> it doesn't answer the above question.

The mpeg4 encoder encodes differently than the x264 encoder. You *may*
find settings where both achieve the same quality at the same video
bitrate, but that would take a lot of experimenting. (Note: encoding is
mostly a trade-off between bitrate/stream size, quality, and encoding
time. And the actual codec used.) Usually, an MPEG4 stream at approx.
the same quality as an H.264 stream will use significantly more
size/bandwith/bitrate. (Very generally speaking.)

That your mpeg4 video turned out much smaller is due to the fact that
ffmpeg's mpeg4 setting defaults to "200kbit/s CBR with best effort",
regardless of resolution. ffmpeg's x264 default is "CRF 23, VBR", which
tends to (well, almost always will) result in much higher quality at
sane resolutions, e.g. 480p upwards.

> > (Which, again - for everyone - is the
> > reason we request to see it. ;-))
> Obviously you didn't view my post to the end. There it is.

I did. I even quoted it. I just wanted to emphasize this for everyone
else, since it proves the point.

> Please have a thought on my question 1.)
> Where in the documentation I find, which quality is used by default and
> how to change it?
> In other words, wouldn't it make sense to add this, if this information
> is missing?

IMHO it would make sense, especially as "ffmpeg -h encoder=blafoo"
cannot tell you.

Moritz
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Re: Confusion about quality parameters

Ulf Zibis

Am 26.06.19 um 09:58 schrieb Moritz Barsnick:
> This has nothing to do with the dev branch, only with your particular
> build. It uses different codecs, and these behave totally differently -
> both by nature, and by default settings.

> The mpeg4 encoder encodes differently than the x264 encoder. You *may*
> find settings where both achieve the same quality at the same video
> bitrate, but that would take a lot of experimenting. (Note: encoding is
> mostly a trade-off between bitrate/stream size, quality, and encoding
> time. And the actual codec used.) Usually, an MPEG4 stream at approx.
> the same quality as an H.264 stream will use significantly more
> size/bandwith/bitrate. (Very generally speaking.)
>
> That your mpeg4 video turned out much smaller is due to the fact that
> ffmpeg's mpeg4 setting defaults to "200kbit/s CBR with best effort",
> regardless of resolution. ffmpeg's x264 default is "CRF 23, VBR", which
> tends to (well, almost always will) result in much higher quality at
> sane resolutions, e.g. 480p upwards.
Much thanks, as this is more than I wanted to know.
Now I fully understand :-)

>> Please have a thought on my question 1.)
>> Where in the documentation I find, which quality is used by default and
>> how to change it?
>> In other words, wouldn't it make sense to add this, if this information
>> is missing?
> IMHO it would make sense, especially as "ffmpeg -h encoder=blafoo"
> cannot tell you.

Thanks! Here my report: https://trac.ffmpeg.org/ticket/7973#ticket

-Ulf

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