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Size of cropped video segments

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Size of cropped video segments

Chao Zhou
Hi team,

I am cropping a video to 9 small segments with the command below:

ffmpeg -i source.mp4 -filter_complex \
"[0:v]crop=1/3*in_w:1/3*in_h:0:0[out1];[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:0[out2];\
[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:0[out3];[0:v]crop=1/3*in_w:1/3*in_h:0:1/3*in_h[out4];\
[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:1/3*in_h[out5];[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:1/3*in_h[out6];\
[0:v]crop=1/3*in_w:1/3*in_h:0:2/3*in_h[out7];[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:2/3*in_h[out8];[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:2/3*in_h[out9]"
\
-map "[out1]" out1.mp4 -map "[out2]" out2.mp4 -map "[out3]" out3.mp4 \
-map "[out4]" out4.mp4 -map "[out5]" out5.mp4 -map "[out6]" out6.mp4 \
-map "[out7]" out7.mp4 -map "[out8]" out8.mp4 -map "[out9]" out9.mp4

I expect the size of total 9 segments will be larger than the source video
since the search space of the segment became smaller and encoding
efficiency reduced. It is true for 720p and 1080p videos downloaded from
youtube. However, the size of total 9 segments for 1440p video and 4K video
became smaller compared with source video.

Can anyone please help me explain this situation?

Thanks.
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Re: Size of cropped video segments

Carl Eugen Hoyos-2
2017-02-08 17:29 GMT+01:00 Chao Zhou <[hidden email]>:

> I am cropping a video to 9 small segments with the command below:
>
> ffmpeg -i source.mp4 -filter_complex \
> "[0:v]crop=1/3*in_w:1/3*in_h:0:0[out1];[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:0[out2];\
> [0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:0[out3];[0:v]crop=1/3*in_w:1/3*in_h:0:1/3*in_h[out4];\
> [0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:1/3*in_h[out5];[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:1/3*in_h[out6];\
> [0:v]crop=1/3*in_w:1/3*in_h:0:2/3*in_h[out7];[0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:2/3*in_h[out8];[0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:2/3*in_h[out9]"
> \
> -map "[out1]" out1.mp4 -map "[out2]" out2.mp4 -map "[out3]" out3.mp4 \
> -map "[out4]" out4.mp4 -map "[out5]" out5.mp4 -map "[out6]" out6.mp4 \
> -map "[out7]" out7.mp4 -map "[out8]" out8.mp4 -map "[out9]" out9.mp4

Complete, uncut console output missing.

> I expect the size of total 9 segments will be larger than the source video

Why?

> since the search space of the segment became smaller and encoding
> efficiency reduced.

Even if this were a valid argument (I apparently misunderstand it due to
the language barrier) it is certainly not a sufficient argument for a bigger
(or smaller) filesize: You can either specify a bitrate or output quality (which
is the default for x264), in case of quality several other factors are
responsible for the output filesize.

Carl Eugen
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Re: Size of cropped video segments

Chao Zhou
Carl,

Thanks for your reply.

> I expect the size of total 9 segments will be larger than the source video

When encoding source video, the P/B frame can search previous full size I
frame to reduce their encoding size. After cropping, each of these video
segments has a smaller size of I frame. Then, the following P/B frame have
to encode more redundant data for correct recovery on the decoder side. Is
it right? I didn't change any bitrate or video quality parameters during
cropping process.

Again, thanks for your help. This question confuses me for a while. I put
the complete console output below:

ffmpeg version N-80924-gb450b82 Copyright (c) 2000-2016 the FFmpeg
developers
  built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.3)
  configuration: --prefix=/home/chao/ffmpeg_build
--pkg-config-flags=--static
--extra-cflags=-I/home/chao/ffmpeg_build/include
--extra-ldflags=-L/home/chao/ffmpeg_build/lib --bindir=/home/chao/bin
--enable-gpl --enable-libass --enable-libfreetype --enable-libtheora
--enable-libvorbis --enable-libx264 --enable-nonfree
  libavutil      55. 28.100 / 55. 28.100
  libavcodec     57. 48.103 / 57. 48.103
  libavformat    57. 41.100 / 57. 41.100
  libavdevice    57.  0.102 / 57.  0.102
  libavfilter     6. 47.100 /  6. 47.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  1.100 /  2.  1.100
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'source.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    creation_time   : 2017-01-18 08:24:19
  Duration: 00:00:32.50, start: 0.000000, bitrate: 5542 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv,
bt709), 2560x1440 [SAR 1:1 DAR 16:9], 924 kb/s, 29.97 fps, 29.97 tbr, 90k
tbn, 59.94 tbc (default)
    Metadata:
      creation_time   : 2017-01-18 08:24:19
      handler_name    : VideoHandler
[libx264 @ 0x332d380] using SAR=1/1
[libx264 @ 0x332d380] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x332d380] profile High, level 3.1
[libx264 @ 0x332d380] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x33087a0] using SAR=1/1
[libx264 @ 0x33087a0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x33087a0] profile High, level 3.1
[libx264 @ 0x33087a0] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x330a600] using SAR=1/1
[libx264 @ 0x330a600] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x330a600] profile High, level 3.1
[libx264 @ 0x330a600] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x346d7a0] using SAR=1/1
[libx264 @ 0x346d7a0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x346d7a0] profile High, level 3.1
[libx264 @ 0x346d7a0] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x3470160] using SAR=1/1
[libx264 @ 0x3470160] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x3470160] profile High, level 3.1
[libx264 @ 0x3470160] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x3472780] using SAR=1/1
[libx264 @ 0x3472780] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x3472780] profile High, level 3.1
[libx264 @ 0x3472780] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x3324ce0] using SAR=1/1
[libx264 @ 0x3324ce0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x3324ce0] profile High, level 3.1
[libx264 @ 0x3324ce0] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x3327420] using SAR=1/1
[libx264 @ 0x3327420] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x3327420] profile High, level 3.1
[libx264 @ 0x3327420] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[libx264 @ 0x3329b20] using SAR=1/1
[libx264 @ 0x3329b20] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x3329b20] profile High, level 3.1
[libx264 @ 0x3329b20] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec
- Copyleft 2003-2014 - 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=6 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
[mp4 @ 0x34af900] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x34b01c0] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x33096c0] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x346c860] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x346edc0] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x34713e0] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x3323da0] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x3326140] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x3328780] Using AVStream.codec to pass codec parameters to muxers
is deprecated, use AVStream.codecpar instead.
Output #0, mp4, to 'out1.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #1, mp4, to 'out2.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #1:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #2, mp4, to 'out3.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #2:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #3, mp4, to 'out4.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #3:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #4, mp4, to 'out5.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #4:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #5, mp4, to 'out6.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #5:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #6, mp4, to 'out7.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #6:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #7, mp4, to 'out8.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #7:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Output #8, mp4, to 'out9.mp4':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6avc1mp41
    encoder         : Lavf57.41.100
    Stream #8:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p,
852x480 [SAR 1:1 DAR 71:40], q=-1--1, 29.97 fps, 30k tbn, 29.97 tbc
(default)
    Metadata:
      encoder         : Lavc57.48.103 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream mapping:
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  Stream #0:0 (h264) -> crop
  crop -> Stream #0:0 (libx264)
  crop -> Stream #1:0 (libx264)
  crop -> Stream #2:0 (libx264)
  crop -> Stream #3:0 (libx264)
  crop -> Stream #4:0 (libx264)
  crop -> Stream #5:0 (libx264)
  crop -> Stream #6:0 (libx264)
  crop -> Stream #7:0 (libx264)
  crop -> Stream #8:0 (libx264)
Press [q] to stop, [?] for help
frame=  974 fps= 31 q=-1.0 Lq=-1.0 q=-1.0 q=-1.0 q=-1.0 q=-1.0 q=-1.0
q=-1.0 q=-1.0 size=    1177kB time=00:00:32.39 bitrate= 297.6kbits/s
speed=1.02x
video:21360kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknown
[libx264 @ 0x332d380] frame I:4     Avg QP:18.31  size: 33702
[libx264 @ 0x332d380] frame P:261   Avg QP:20.60  size:  3323
[libx264 @ 0x332d380] frame B:709   Avg QP:25.26  size:   268
[libx264 @ 0x332d380] consecutive B-frames:  2.8%  0.4%  0.3% 96.5%
[libx264 @ 0x332d380] mb I  I16..4:  4.4% 75.0% 20.6%
[libx264 @ 0x332d380] mb P  I16..4:  0.7%  0.7%  0.1%  P16..4: 31.0% 10.0%
 6.5%  0.0%  0.0%    skip:51.0%
[libx264 @ 0x332d380] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8: 21.2%  0.1%
 0.0%  direct: 0.0%  skip:78.7%  L0:35.9% L1:63.8% BI: 0.3%
[libx264 @ 0x332d380] 8x8 transform intra:61.3% inter:77.1%
[libx264 @ 0x332d380] coded y,uvDC,uvAC intra: 65.2% 41.7% 8.9% inter: 4.6%
4.2% 0.0%
[libx264 @ 0x332d380] i16 v,h,dc,p:  2% 88%  4%  6%
[libx264 @ 0x332d380] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  6% 47% 10%  6%  3%
 2%  7%  4% 14%
[libx264 @ 0x332d380] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 10% 49%  7%  5%  5%
 3%  8%  3% 10%
[libx264 @ 0x332d380] i8c dc,h,v,p: 60% 26% 11%  4%
[libx264 @ 0x332d380] Weighted P-Frames: Y:1.9% UV:0.0%
[libx264 @ 0x332d380] ref P L0: 64.6% 14.6% 16.3%  4.4%  0.2%
[libx264 @ 0x332d380] ref B L0: 92.6%  6.3%  1.1%
[libx264 @ 0x332d380] ref B L1: 97.9%  2.1%
[libx264 @ 0x332d380] kb/s:293.42
[libx264 @ 0x33087a0] frame I:4     Avg QP:19.31  size: 47992
[libx264 @ 0x33087a0] frame P:304   Avg QP:21.49  size:  3783
[libx264 @ 0x33087a0] frame B:666   Avg QP:27.12  size:   336
[libx264 @ 0x33087a0] consecutive B-frames:  8.2%  0.8%  3.1% 87.9%
[libx264 @ 0x33087a0] mb I  I16..4:  4.4% 57.1% 38.5%
[libx264 @ 0x33087a0] mb P  I16..4:  0.4%  0.5%  0.2%  P16..4: 32.4%  8.4%
 6.6%  0.0%  0.0%    skip:51.4%
[libx264 @ 0x33087a0] mb B  I16..4:  0.0%  0.1%  0.0%  B16..8: 19.5%  0.2%
 0.1%  direct: 0.1%  skip:80.0%  L0:27.0% L1:72.4% BI: 0.6%
[libx264 @ 0x33087a0] 8x8 transform intra:50.5% inter:62.9%
[libx264 @ 0x33087a0] coded y,uvDC,uvAC intra: 73.2% 58.5% 23.0% inter:
6.0% 5.8% 0.1%
[libx264 @ 0x33087a0] i16 v,h,dc,p:  0% 92%  1%  6%
[libx264 @ 0x33087a0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 44%  9%  5%  5%
 3% 11%  4% 12%
[libx264 @ 0x33087a0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11% 27%  9%  6% 11%
 5% 17%  5% 11%
[libx264 @ 0x33087a0] i8c dc,h,v,p: 53% 31% 11%  5%
[libx264 @ 0x33087a0] Weighted P-Frames: Y:2.0% UV:0.0%
[libx264 @ 0x33087a0] ref P L0: 69.2% 13.4% 13.0%  4.1%  0.3%
[libx264 @ 0x33087a0] ref B L0: 93.0%  5.5%  1.6%
[libx264 @ 0x33087a0] ref B L1: 97.7%  2.3%
[libx264 @ 0x33087a0] kb/s:385.37
[libx264 @ 0x330a600] frame I:4     Avg QP:18.23  size: 25925
[libx264 @ 0x330a600] frame P:265   Avg QP:20.37  size:  2882
[libx264 @ 0x330a600] frame B:705   Avg QP:24.34  size:   280
[libx264 @ 0x330a600] consecutive B-frames:  3.4%  0.2%  0.3% 96.1%
[libx264 @ 0x330a600] mb I  I16..4:  6.0% 76.9% 17.1%
[libx264 @ 0x330a600] mb P  I16..4:  0.8%  1.1%  0.1%  P16..4: 30.6%  9.2%
 5.6%  0.0%  0.0%    skip:52.5%
[libx264 @ 0x330a600] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8: 19.3%  0.1%
 0.0%  direct: 0.0%  skip:80.5%  L0:32.4% L1:67.1% BI: 0.5%
[libx264 @ 0x330a600] 8x8 transform intra:63.9% inter:83.3%
[libx264 @ 0x330a600] coded y,uvDC,uvAC intra: 57.5% 47.8% 13.4% inter:
4.0% 6.0% 0.0%
[libx264 @ 0x330a600] i16 v,h,dc,p:  4% 80%  4% 11%
[libx264 @ 0x330a600] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  9% 41% 15%  2%  7%
 4% 14%  3%  6%
[libx264 @ 0x330a600] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 12% 42%  9%  3%  8%
 4% 13%  3%  5%
[libx264 @ 0x330a600] i8c dc,h,v,p: 57% 31%  7%  4%
[libx264 @ 0x330a600] Weighted P-Frames: Y:1.5% UV:0.0%
[libx264 @ 0x330a600] ref P L0: 66.9% 11.7% 16.6%  4.6%  0.2%
[libx264 @ 0x330a600] ref B L0: 91.1%  7.6%  1.3%
[libx264 @ 0x330a600] ref B L1: 97.9%  2.1%
[libx264 @ 0x330a600] kb/s:262.21
[libx264 @ 0x346d7a0] frame I:4     Avg QP:20.88  size: 70714
[libx264 @ 0x346d7a0] frame P:491   Avg QP:23.67  size:  7885
[libx264 @ 0x346d7a0] frame B:479   Avg QP:30.92  size:  1140
[libx264 @ 0x346d7a0] consecutive B-frames: 18.8% 30.0% 50.8%  0.4%
[libx264 @ 0x346d7a0] mb I  I16..4:  3.5% 45.5% 51.0%
[libx264 @ 0x346d7a0] mb P  I16..4:  0.4%  1.1%  0.6%  P16..4: 28.7% 13.1%
11.7%  0.0%  0.0%    skip:44.3%
[libx264 @ 0x346d7a0] mb B  I16..4:  0.0%  0.1%  0.1%  B16..8: 16.3%  2.5%
 1.0%  direct: 1.3%  skip:78.7%  L0:23.0% L1:67.0% BI:10.1%
[libx264 @ 0x346d7a0] 8x8 transform intra:49.8% inter:50.5%
[libx264 @ 0x346d7a0] coded y,uvDC,uvAC intra: 64.0% 70.6% 37.7% inter:
12.5% 9.9% 0.8%
[libx264 @ 0x346d7a0] i16 v,h,dc,p: 20% 38% 16% 27%
[libx264 @ 0x346d7a0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 20% 21% 20%  4%  6%
 9%  6%  6%  7%
[libx264 @ 0x346d7a0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 23% 23% 13%  5%  7%
10%  6%  7%  6%
[libx264 @ 0x346d7a0] i8c dc,h,v,p: 47% 24% 21%  8%
[libx264 @ 0x346d7a0] Weighted P-Frames: Y:0.8% UV:0.0%
[libx264 @ 0x346d7a0] ref P L0: 74.5% 16.0%  7.0%  2.4%  0.0%
[libx264 @ 0x346d7a0] ref B L0: 92.9%  6.1%  1.0%
[libx264 @ 0x346d7a0] ref B L1: 95.8%  4.2%
[libx264 @ 0x346d7a0] kb/s:1157.12
[libx264 @ 0x3470160] frame I:4     Avg QP:19.75  size: 53669
[libx264 @ 0x3470160] frame P:474   Avg QP:22.07  size:  6808
[libx264 @ 0x3470160] frame B:496   Avg QP:31.07  size:  1126
[libx264 @ 0x3470160] consecutive B-frames: 21.3% 13.8% 56.4%  8.6%
[libx264 @ 0x3470160] mb I  I16..4:  3.8% 56.6% 39.6%
[libx264 @ 0x3470160] mb P  I16..4:  0.2%  1.2%  0.7%  P16..4: 26.3%  9.8%
 8.4%  0.0%  0.0%    skip:53.3%
[libx264 @ 0x3470160] mb B  I16..4:  0.0%  0.2%  0.1%  B16..8: 11.4%  2.5%
 1.0%  direct: 1.3%  skip:83.6%  L0:25.1% L1:63.3% BI:11.6%
[libx264 @ 0x3470160] 8x8 transform intra:56.6% inter:49.5%
[libx264 @ 0x3470160] coded y,uvDC,uvAC intra: 74.5% 77.6% 42.7% inter:
10.9% 9.8% 0.7%
[libx264 @ 0x3470160] i16 v,h,dc,p: 13% 42% 11% 35%
[libx264 @ 0x3470160] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 17% 20% 17%  5%  8%
 7%  9%  8%  9%
[libx264 @ 0x3470160] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 23% 12%  6%  7%
 8%  7%  8%  6%
[libx264 @ 0x3470160] i8c dc,h,v,p: 46% 26% 19%  9%
[libx264 @ 0x3470160] Weighted P-Frames: Y:1.1% UV:0.0%
[libx264 @ 0x3470160] ref P L0: 75.4% 14.3%  7.5%  2.7%  0.1%
[libx264 @ 0x3470160] ref B L0: 92.0%  6.7%  1.3%
[libx264 @ 0x3470160] ref B L1: 95.3%  4.7%
[libx264 @ 0x3470160] kb/s:984.67
[libx264 @ 0x3472780] frame I:4     Avg QP:19.97  size: 53794
[libx264 @ 0x3472780] frame P:359   Avg QP:22.87  size:  8618
[libx264 @ 0x3472780] frame B:611   Avg QP:29.16  size:   988
[libx264 @ 0x3472780] consecutive B-frames:  6.3%  6.8% 70.5% 16.4%
[libx264 @ 0x3472780] mb I  I16..4:  5.0% 57.3% 37.7%
[libx264 @ 0x3472780] mb P  I16..4:  0.8%  1.9%  0.5%  P16..4: 33.0% 17.4%
12.9%  0.0%  0.0%    skip:33.5%
[libx264 @ 0x3472780] mb B  I16..4:  0.0%  0.1%  0.0%  B16..8: 21.7%  2.3%
 0.7%  direct: 1.0%  skip:74.2%  L0:27.2% L1:65.2% BI: 7.6%
[libx264 @ 0x3472780] 8x8 transform intra:59.1% inter:58.4%
[libx264 @ 0x3472780] coded y,uvDC,uvAC intra: 54.2% 61.8% 24.3% inter:
10.4% 9.5% 0.6%
[libx264 @ 0x3472780] i16 v,h,dc,p: 36% 29% 13% 23%
[libx264 @ 0x3472780] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 23% 22% 24%  4%  5%
 6%  5%  6%  6%
[libx264 @ 0x3472780] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 29% 11%  5%  6%
 7%  6%  7%  6%
[libx264 @ 0x3472780] i8c dc,h,v,p: 50% 26% 19%  6%
[libx264 @ 0x3472780] Weighted P-Frames: Y:0.8% UV:0.0%
[libx264 @ 0x3472780] ref P L0: 68.7% 15.6% 12.3%  3.4%  0.1%
[libx264 @ 0x3472780] ref B L0: 90.9%  8.0%  1.1%
[libx264 @ 0x3472780] ref B L1: 94.4%  5.6%
[libx264 @ 0x3472780] kb/s:963.13
[libx264 @ 0x3324ce0] frame I:4     Avg QP:19.16  size: 34946
[libx264 @ 0x3324ce0] frame P:320   Avg QP:21.34  size:  4303
[libx264 @ 0x3324ce0] frame B:650   Avg QP:24.23  size:   704
[libx264 @ 0x3324ce0] consecutive B-frames: 10.4%  0.8%  3.4% 85.4%
[libx264 @ 0x3324ce0] mb I  I16..4: 18.7% 51.4% 29.9%
[libx264 @ 0x3324ce0] mb P  I16..4:  6.4%  6.6%  0.3%  P16..4: 36.5%  8.3%
 4.3%  0.0%  0.0%    skip:37.5%
[libx264 @ 0x3324ce0] mb B  I16..4:  0.4%  0.4%  0.0%  B16..8: 23.9%  0.9%
 0.1%  direct: 1.2%  skip:73.0%  L0:39.4% L1:58.7% BI: 2.0%
[libx264 @ 0x3324ce0] 8x8 transform intra:49.9% inter:80.9%
[libx264 @ 0x3324ce0] coded y,uvDC,uvAC intra: 20.2% 57.7% 11.8% inter:
5.6% 13.4% 0.5%
[libx264 @ 0x3324ce0] i16 v,h,dc,p: 15% 51% 15% 20%
[libx264 @ 0x3324ce0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 13% 36% 39%  2%  2%
 1%  3%  1%  3%
[libx264 @ 0x3324ce0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 14% 42% 13%  4%  5%
 4%  7%  4%  6%
[libx264 @ 0x3324ce0] i8c dc,h,v,p: 42% 41% 12%  5%
[libx264 @ 0x3324ce0] Weighted P-Frames: Y:1.2% UV:0.0%
[libx264 @ 0x3324ce0] ref P L0: 65.7% 14.6% 14.1%  5.6%  0.0%
[libx264 @ 0x3324ce0] ref B L0: 89.8%  7.5%  2.6%
[libx264 @ 0x3324ce0] ref B L1: 96.8%  3.2%
[libx264 @ 0x3324ce0] kb/s:485.92
[libx264 @ 0x3327420] frame I:4     Avg QP:18.64  size: 22255
[libx264 @ 0x3327420] frame P:349   Avg QP:20.34  size:  3018
[libx264 @ 0x3327420] frame B:621   Avg QP:21.98  size:   492
[libx264 @ 0x3327420] consecutive B-frames: 10.3%  9.0% 15.4% 65.3%
[libx264 @ 0x3327420] mb I  I16..4: 22.7% 52.8% 24.6%
[libx264 @ 0x3327420] mb P  I16..4:  7.6%  7.5%  0.2%  P16..4: 31.5%  5.5%
 2.6%  0.0%  0.0%    skip:45.0%
[libx264 @ 0x3327420] mb B  I16..4:  0.4%  0.2%  0.0%  B16..8: 18.6%  0.4%
 0.0%  direct: 1.3%  skip:79.1%  L0:37.9% L1:61.2% BI: 0.9%
[libx264 @ 0x3327420] 8x8 transform intra:48.4% inter:89.5%
[libx264 @ 0x3327420] coded y,uvDC,uvAC intra: 17.1% 51.4% 12.5% inter:
4.3% 11.9% 0.2%
[libx264 @ 0x3327420] i16 v,h,dc,p: 21% 56% 13% 10%
[libx264 @ 0x3327420] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 14% 26% 48%  1%  3%
 2%  3%  1%  2%
[libx264 @ 0x3327420] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 40% 17%  3%  5%
 2%  8%  1%  6%
[libx264 @ 0x3327420] i8c dc,h,v,p: 47% 40% 10%  2%
[libx264 @ 0x3327420] Weighted P-Frames: Y:2.0% UV:0.0%
[libx264 @ 0x3327420] ref P L0: 65.6% 12.0% 15.7%  6.7%  0.1%
[libx264 @ 0x3327420] ref B L0: 86.1% 10.8%  3.0%
[libx264 @ 0x3327420] ref B L1: 95.4%  4.6%
[libx264 @ 0x3327420] kb/s:356.45
[libx264 @ 0x3329b20] frame I:4     Avg QP:19.95  size: 28494
[libx264 @ 0x3329b20] frame P:261   Avg QP:21.96  size:  5269
[libx264 @ 0x3329b20] frame B:709   Avg QP:24.69  size:   732
[libx264 @ 0x3329b20] consecutive B-frames:  2.5%  0.6%  2.5% 94.5%
[libx264 @ 0x3329b20] mb I  I16..4: 15.6% 61.0% 23.4%
[libx264 @ 0x3329b20] mb P  I16..4:  6.0%  6.1%  0.3%  P16..4: 40.4% 13.5%
 6.2%  0.0%  0.0%    skip:27.6%
[libx264 @ 0x3329b20] mb B  I16..4:  0.2%  0.2%  0.0%  B16..8: 25.9%  1.2%
 0.1%  direct: 0.7%  skip:71.7%  L0:39.9% L1:57.3% BI: 2.8%
[libx264 @ 0x3329b20] 8x8 transform intra:50.2% inter:81.3%
[libx264 @ 0x3329b20] coded y,uvDC,uvAC intra: 23.6% 59.7% 15.0% inter:
6.0% 12.3% 0.4%
[libx264 @ 0x3329b20] i16 v,h,dc,p:  8% 67%  7% 18%
[libx264 @ 0x3329b20] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 14% 39% 30%  2%  2%
 2%  4%  2%  4%
[libx264 @ 0x3329b20] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 18% 35% 13%  5%  6%
 4%  9%  4%  5%
[libx264 @ 0x3329b20] i8c dc,h,v,p: 40% 46%  8%  5%
[libx264 @ 0x3329b20] Weighted P-Frames: Y:2.3% UV:0.0%
[libx264 @ 0x3329b20] ref P L0: 63.7% 13.9% 17.2%  5.0%  0.2%
[libx264 @ 0x3329b20] ref B L0: 92.0%  6.4%  1.6%
[libx264 @ 0x3329b20] ref B L1: 97.3%  2.7%
[libx264 @ 0x3329b20] kb/s:494.38


On Wed, Feb 8, 2017 at 5:52 PM, Carl Eugen Hoyos <[hidden email]> wrote:

> 2017-02-08 17:29 GMT+01:00 Chao Zhou <[hidden email]>:
>
> > I am cropping a video to 9 small segments with the command below:
> >
> > ffmpeg -i source.mp4 -filter_complex \
> > "[0:v]crop=1/3*in_w:1/3*in_h:0:0[out1];[0:v]crop=1/3*in_w:
> 1/3*in_h:1/3*in_w:0[out2];\
> > [0:v]crop=1/3*in_w:1/3*in_h:2/3*in_w:0[out3];[0:v]crop=1/3*
> in_w:1/3*in_h:0:1/3*in_h[out4];\
> > [0:v]crop=1/3*in_w:1/3*in_h:1/3*in_w:1/3*in_h[out5];[0:v]
> crop=1/3*in_w:1/3*in_h:2/3*in_w:1/3*in_h[out6];\
> > [0:v]crop=1/3*in_w:1/3*in_h:0:2/3*in_h[out7];[0:v]crop=1/3*
> in_w:1/3*in_h:1/3*in_w:2/3*in_h[out8];[0:v]crop=1/3*in_w:1/
> 3*in_h:2/3*in_w:2/3*in_h[out9]"
> > \
> > -map "[out1]" out1.mp4 -map "[out2]" out2.mp4 -map "[out3]" out3.mp4 \
> > -map "[out4]" out4.mp4 -map "[out5]" out5.mp4 -map "[out6]" out6.mp4 \
> > -map "[out7]" out7.mp4 -map "[out8]" out8.mp4 -map "[out9]" out9.mp4
>
> Complete, uncut console output missing.
>
> > I expect the size of total 9 segments will be larger than the source
> video
>
> Why?
>
> > since the search space of the segment became smaller and encoding
> > efficiency reduced.
>
> Even if this were a valid argument (I apparently misunderstand it due to
> the language barrier) it is certainly not a sufficient argument for a
> bigger
> (or smaller) filesize: You can either specify a bitrate or output quality
> (which
> is the default for x264), in case of quality several other factors are
> responsible for the output filesize.
>
> Carl Eugen
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Re: Size of cropped video segments

Moritz Barsnick
On Thu, Feb 09, 2017 at 09:39:13 -0500, Chao Zhou wrote:
> > I expect the size of total 9 segments will be larger than the source video
>
> When encoding source video, the P/B frame can search previous full size I
> frame to reduce their encoding size. After cropping, each of these video
> segments has a smaller size of I frame. Then, the following P/B frame have
> to encode more redundant data for correct recovery on the decoder side. Is
> it right? I didn't change any bitrate or video quality parameters during
> cropping process.

You did change them, because you decode the original video and then
reencode it with ffmpeg/libx264. The resulting bitrate depends on
various parameters, which are not related to the original video:
encoding profile and level, CRF value, various other encoding
parameters, and last not least encoding efficiency of the utilized
encoder. You can probably vary the bitrate by about a factor of 10x
with little variation in the visual output quality. (YMMV)

If you use a different H.264 encoder, you will most likely get
different results as well!

To get back to your original question as to why your observed relation
no longer applied to "larger scale" videos: Perhaps the originals were
*less* efficiently encoded, so the sum of your segment encodings became
relatively smaller. Or they were different material (less motion,
animation, or so) leading to better encoding efficiency. Or - long
shot, and I doubt it - something else made the encoder more efficient
at the higher resolutions.

> [libx264 @ 0x332d380] frame I:4     Avg QP:18.31  size: 33702
> [libx264 @ 0x332d380] frame P:261   Avg QP:20.60  size:  3323
> [libx264 @ 0x332d380] frame B:709   Avg QP:25.26  size:   268
> [libx264 @ 0x332d380] consecutive B-frames:  2.8%  0.4%  0.3% 96.5%

You might want to compare some of these statistics. On the other hand,
they may be misleading - I don't really know. ;-)

Moritz
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Re: Size of cropped video segments

Chao Zhou
Hi Moritz,

Thank you!

I do have some tests that reencoding source videos with same ffmpeg/libx264
setting first, then cropped the video to small segments. The problem
remains the same. However, your opinion about less motion or animation
enlightens me; If the moving object of the source video just stays within
one of the small segments, others of segments may have better encoding
efficiency since they are more static.

Hopefully, this guess can be proven by some experts ~ :-)

Chao


On Thu, Feb 9, 2017 at 11:25 AM, Moritz Barsnick <[hidden email]> wrote:

> On Thu, Feb 09, 2017 at 09:39:13 -0500, Chao Zhou wrote:
> > > I expect the size of total 9 segments will be larger than the source
> video
> >
> > When encoding source video, the P/B frame can search previous full size I
> > frame to reduce their encoding size. After cropping, each of these video
> > segments has a smaller size of I frame. Then, the following P/B frame
> have
> > to encode more redundant data for correct recovery on the decoder side.
> Is
> > it right? I didn't change any bitrate or video quality parameters during
> > cropping process.
>
> You did change them, because you decode the original video and then
> reencode it with ffmpeg/libx264. The resulting bitrate depends on
> various parameters, which are not related to the original video:
> encoding profile and level, CRF value, various other encoding
> parameters, and last not least encoding efficiency of the utilized
> encoder. You can probably vary the bitrate by about a factor of 10x
> with little variation in the visual output quality. (YMMV)
>
> If you use a different H.264 encoder, you will most likely get
> different results as well!
>
> To get back to your original question as to why your observed relation
> no longer applied to "larger scale" videos: Perhaps the originals were
> *less* efficiently encoded, so the sum of your segment encodings became
> relatively smaller. Or they were different material (less motion,
> animation, or so) leading to better encoding efficiency. Or - long
> shot, and I doubt it - something else made the encoder more efficient
> at the higher resolutions.
>
> > [libx264 @ 0x332d380] frame I:4     Avg QP:18.31  size: 33702
> > [libx264 @ 0x332d380] frame P:261   Avg QP:20.60  size:  3323
> > [libx264 @ 0x332d380] frame B:709   Avg QP:25.26  size:   268
> > [libx264 @ 0x332d380] consecutive B-frames:  2.8%  0.4%  0.3% 96.5%
>
> You might want to compare some of these statistics. On the other hand,
> they may be misleading - I don't really know. ;-)
>
> Moritz
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> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
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> [hidden email] with subject "unsubscribe".
>
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