why ffplay cannot decode a sequence that can be decoded by ffmpeg

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why ffplay cannot decode a sequence that can be decoded by ffmpeg

mohammed bey ahmed khernache
Hello,
I have a video encoded with HEVC.
Is there a reason why *ffmpeg* can decode it whereas *ffplay* can not?

Thank you
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Moritz Barsnick
On Thu, Jun 07, 2018 at 16:50:32 +0200, mohammed bey ahmed khernache wrote:
> Hello,
> I have a video encoded with HEVC.
> Is there a reason why *ffmpeg* can decode it whereas *ffplay* can not?

Yes, perhaps.

Instead of letting us guess, you could provide both your command lines
(i.e. of both ffmpeg and ffplay) and each of their uncut console
outputs. ffplay does for example show warnings and error messages, they
are not there for pure fun, but to indicate what went wrong.

(Please use the commands *without* "-hide_banner" and without changing
the default loglevel.)

Thanks,
Moritz
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

mohammed bey ahmed khernache
Thank you for your quick reply.

----------------------------- ffplay command line
---------------------------------------------
ffplay -nodisp -autoexit <input_video>
----------------------------- ffplay output
-------------------------------------------------------
root@odroid:~/HEVC# ffplay -nodisp -autoexit Tears_400_x265.mp4 >
ffplay_output
ffplay version N-91111-g380ca1bc Copyright (c) 2003-2018 the FFmpeg
developers
  built with gcc 4.8 (Ubuntu/Linaro 4.8.2-19ubuntu1)
  configuration: --prefix=/root/ffmpeg_build --pkg-config-flags=--static
--extra-cflags=-I/root/ffmpeg_build/include
--extra-ldflags=-L/root/ffmpeg_build/lib --extra-libs='-lpthread -lm'
--bindir=/root/bin --enable-gpl --enable-libass --enable-libfdk-aac
--enable-libfreetype --enable-libmp3lame --enable-libopus
--enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264
--enable-libx265 --arch=arm --arch=arm --enable-neon --enable-thumb
--enable-optimizations --enable-pthreads --enable-gray --enable-version3
--enable-postproc --enable-libxcb --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libdc1394 --enable-libgsm
--enable-libopenjpeg --enable-libspeex --enable-libtheora
--enable-libvorbis --enable-libxvid --enable-yasm --enable-nonfree
  libavutil      56. 18.102 / 56. 18.102
  libavcodec     58. 19.102 / 58. 19.102
  libavformat    58. 13.102 / 58. 13.102
  libavdevice    58.  4.100 / 58.  4.100
  libavfilter     7. 23.100 /  7. 23.100
  libswscale      5.  2.100 /  5.  2.100
  libswresample   3.  2.100 /  3.  2.100
  libpostproc    55.  2.100 / 55.  2.100
xcb_connection_has_error() returned true
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Tears_400_x265.mp4':=0/0
  Metadata:
    major_brand     : iso4
    minor_version   : 1
    compatible_brands: iso4hvc1
    creation_time   : 2014-08-25T18:10:46.000000Z
  Duration: 00:00:13.96, start: 0.125000, bitrate: 404 kb/s
    Stream #0:0(und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv),
1920x800, 402 kb/s, 24 fps, 24 tbr, 24k tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2014-08-25T18:10:46.000000Z
      handler_name    : hevc:fps=24@GPAC0.5.1-DEV-rev4807
Failed to open file 'Tears_400_x265.mp4' or configure filtergraph
______________________________________________________________
-------------------------------------------------------------------------------------------------------

----------------------------- ffmpeg command line
---------------------------------------------
ffmpeg -benchmark -i <input_video> -f null /dev/null
----------------------------- ffmpeg output
-------------------------------------------------------
root@odroid:~/HEVC# ffmpeg -benchmark -i Tears_400_x265.mp4 -f null
/dev/null
ffmpeg version N-91111-g380ca1bc Copyright (c) 2000-2018 the FFmpeg
developers
  built with gcc 4.8 (Ubuntu/Linaro 4.8.2-19ubuntu1)
  configuration: --prefix=/root/ffmpeg_build --pkg-config-flags=--static
--extra-cflags=-I/root/ffmpeg_build/include
--extra-ldflags=-L/root/ffmpeg_build/lib --extra-libs='-lpthread -lm'
--bindir=/root/bin --enable-gpl --enable-libass --enable-libfdk-aac
--enable-libfreetype --enable-libmp3lame --enable-libopus
--enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264
--enable-libx265 --arch=arm --arch=arm --enable-neon --enable-thumb
--enable-optimizations --enable-pthreads --enable-gray --enable-version3
--enable-postproc --enable-libxcb --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libdc1394 --enable-libgsm
--enable-libopenjpeg --enable-libspeex --enable-libtheora
--enable-libvorbis --enable-libxvid --enable-yasm --enable-nonfree
  libavutil      56. 18.102 / 56. 18.102
  libavcodec     58. 19.102 / 58. 19.102
  libavformat    58. 13.102 / 58. 13.102
  libavdevice    58.  4.100 / 58.  4.100
  libavfilter     7. 23.100 /  7. 23.100
  libswscale      5.  2.100 /  5.  2.100
  libswresample   3.  2.100 /  3.  2.100
  libpostproc    55.  2.100 / 55.  2.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Tears_400_x265.mp4':
  Metadata:
    major_brand     : iso4
    minor_version   : 1
    compatible_brands: iso4hvc1
    creation_time   : 2014-08-25T18:10:46.000000Z
  Duration: 00:00:13.96, start: 0.125000, bitrate: 404 kb/s
    Stream #0:0(und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv),
1920x800, 402 kb/s, 24 fps, 24 tbr, 24k tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2014-08-25T18:10:46.000000Z
      handler_name    : hevc:fps=24@GPAC0.5.1-DEV-rev4807
Stream mapping:
  Stream #0:0 -> #0:0 (hevc (native) -> wrapped_avframe (native))
Press [q] to stop, [?] for help
Output #0, null, to '/dev/null':
  Metadata:
    major_brand     : iso4
    minor_version   : 1
    compatible_brands: iso4hvc1
    encoder         : Lavf58.13.102
    Stream #0:0(und): Video: wrapped_avframe, yuv420p, 1920x800, q=2-31,
200 kb/s, 24 fps, 24 tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2014-08-25T18:10:46.000000Z
      handler_name    : hevc:fps=24@GPAC0.5.1-DEV-rev4807
      encoder         : Lavc58.19.102 wrapped_avframe
frame=  335 fps=103 q=-0.0 Lsize=N/A time=00:00:13.95 bitrate=N/A
speed=4.31x
video:133kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknown
bench: utime=13.910s stime=0.385s rtime=3.281s
bench: maxrss=88464kB
______________________________________________________________
-------------------------------------------------------------------------------------------------------

Thank you again

On Thu, Jun 7, 2018 at 5:04 PM Moritz Barsnick <[hidden email]> wrote:

> On Thu, Jun 07, 2018 at 16:50:32 +0200, mohammed bey ahmed khernache wrote:
> > Hello,
> > I have a video encoded with HEVC.
> > Is there a reason why *ffmpeg* can decode it whereas *ffplay* can not?
>
> Yes, perhaps.
>
> Instead of letting us guess, you could provide both your command lines
> (i.e. of both ffmpeg and ffplay) and each of their uncut console
> outputs. ffplay does for example show warnings and error messages, they
> are not there for pure fun, but to indicate what went wrong.
>
> (Please use the commands *without* "-hide_banner" and without changing
> the default loglevel.)
>
> Thanks,
> Moritz
> _______________________________________________
> ffmpeg-user mailing list
> [hidden email]
> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
>
> To unsubscribe, visit link above, or email
> [hidden email] with subject "unsubscribe".
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Moritz Barsnick
On Thu, Jun 07, 2018 at 17:25:30 +0200, mohammed bey ahmed khernache wrote:
> root@odroid:~/HEVC# ffplay -nodisp -autoexit Tears_400_x265.mp4 > ffplay_output
[...]
> Failed to open file 'Tears_400_x265.mp4' or configure filtergraph

It seems that ffplay has issues with "-nodisp" with files that contain
a video stream, but no audio stream. This must be a bug.

If you don't use "-nodisp", your file should play fine, correct?

Moritz
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

mohammed bey ahmed khernache
I am using ssh, so I cannot run *ffplay *without "-nodisp" option.
I think you are right, *ffplay *can decode videos that contain audio stream
without any problem.
Therefore, it must be a bug in *ffplay*.

Thank you for this note.

On Thu, Jun 7, 2018 at 6:20 PM Moritz Barsnick <[hidden email]> wrote:

> On Thu, Jun 07, 2018 at 17:25:30 +0200, mohammed bey ahmed khernache wrote:
> > root@odroid:~/HEVC# ffplay -nodisp -autoexit Tears_400_x265.mp4 >
> ffplay_output
> [...]
> > Failed to open file 'Tears_400_x265.mp4' or configure filtergraph
>
> It seems that ffplay has issues with "-nodisp" with files that contain
> a video stream, but no audio stream. This must be a bug.
>
> If you don't use "-nodisp", your file should play fine, correct?
>
> Moritz
> _______________________________________________
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> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Moritz Barsnick
On Thu, Jun 07, 2018 at 18:45:32 +0200, mohammed bey ahmed khernache wrote:
> I am using ssh, so I cannot run *ffplay *without "-nodisp" option.

In my case, that's no restriction, because ssh can tunnel X11. I do this once
in a while.

But tell me, what is the use case for "-nodisp"? You only have a video
stream, and you're not showing it. What are you doing?

Moritz
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

mohammed bey ahmed khernache
 > In my case, that's no restriction, because ssh can tunnel X11. I do this
once
in a while.
I have not tried to do that before. When I want to view the video, I
connect to the board via Remote Desktop. For that purpose, I installed the
package "*xrdp*" in my board.
> what is the use case for "-nodisp"?
My purpose is to calculate some metrics such as: fps, miss rate, etc, of
video decoding. So I need only to decode a video without displaying it.


On Thu, Jun 7, 2018 at 11:05 PM Moritz Barsnick <[hidden email]> wrote:

> On Thu, Jun 07, 2018 at 18:45:32 +0200, mohammed bey ahmed khernache wrote:
> > I am using ssh, so I cannot run *ffplay *without "-nodisp" option.
>
> In my case, that's no restriction, because ssh can tunnel X11. I do this
> once
> in a while.
>
> But tell me, what is the use case for "-nodisp"? You only have a video
> stream, and you're not showing it. What are you doing?
>
> Moritz
> _______________________________________________
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> [hidden email]
> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
>
> To unsubscribe, visit link above, or email
> [hidden email] with subject "unsubscribe".
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Carl Eugen Hoyos-2
In reply to this post by mohammed bey ahmed khernache
2018-06-07 17:25 GMT+02:00, mohammed bey ahmed khernache <[hidden email]>:

> xcb_connection_has_error() returned true

I believe this is not an FFplay error, probably SDL.

ffmpeg (the application) supports several audio output
devices like alsa, pulse and oss. They may be what
you need.

Carl Eugen
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Moritz Barsnick
On Sat, Jun 09, 2018 at 21:44:28 +0200, Carl Eugen Hoyos wrote:
> ffmpeg (the application) supports several audio output
> devices like alsa, pulse and oss. They may be what
> you need.

But Mohammed's input video didn't even have an audio stream?

I'm still convinced it's either an ffplay bug, or it's intended.
"The file contains only audio, and '-an' is given, so refuse to play."
"The file contains only video, and '-vn'/'-nodisp' is given, so refuse to play."
"The file contains audio and video, and at least one of them isn't disabled, so go ahead with decoding."

I'm not sure the video decoder is used with '-vn'/'-nodisp', so perhaps
running ffplay like this doesn't fulfill Mohammed's cause.
"ffmpeg -i ... -f null -" may be more effective.

$ ffmpeg -f lavfi -i testsrc -t 10 test.vid.mp4
$ ffmpeg -f lavfi -i sine -t 10 test.aud.mp4
$ ffmpeg -f lavfi -i testsrc -f lavfi -i sine -t 10 test.vid+aud.mp4
$ ffplay -nodisp test.vid+aud.mp4
$ ffplay -nodisp test.aud.mp4
$ ffplay -nodisp test.vid.mp4

The last one fails with said error. So does
$ ffplay -an test.aud.mp4

Moritz
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

mohammed bey ahmed khernache
Hello again,
I tried to run *ffplay* without "-*nodisp*" option, where being connected
to my board via *Remote Desktop Connection*.
Unfortunately, ffplay couldn't play it.
Below is the output:
---------------------------------- output of ffplay
-------------------------------------------------
root@odroid:~/HEVC# ffplay jellyfish-10-mbps-hd-hevc.mkv
ffplay version N-91111-g380ca1bc Copyright (c) 2003-2018 the FFmpeg
developers
  built with gcc 4.8 (Ubuntu/Linaro 4.8.2-19ubuntu1)
  configuration: --prefix=/root/ffmpeg_build --pkg-config-flags=--static
--extra-cflags=-I/root/ffmpeg_build/include
--extra-ldflags=-L/root/ffmpeg_build/lib --extra-libs='-lpthread -lm'
--bindir=/root/bin --enable-gpl --enable-libass --enable-libfdk-aac
--enable-libfreetype --enable-libmp3lame --enable-libopus
--enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264
--enable-libx265 --arch=arm --arch=arm --enable-neon --enable-thumb
--enable-optimizations --enable-pthreads --enable-gray --enable-version3
--enable-postproc --enable-libxcb --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libdc1394 --enable-libgsm
--enable-libopenjpeg --enable-libspeex --enable-libtheora
--enable-libvorbis --enable-libxvid --enable-yasm --enable-nonfree
  libavutil      56. 18.102 / 56. 18.102
  libavcodec     58. 19.102 / 58. 19.102
  libavformat    58. 13.102 / 58. 13.102
  libavdevice    58.  4.100 / 58.  4.100
  libavfilter     7. 23.100 /  7. 23.100
  libswscale      5.  2.100 /  5.  2.100
  libswresample   3.  2.100 /  3.  2.100
  libpostproc    55.  2.100 / 55.  2.100
Input #0, matroska,webm, from 'jellyfish-10-mbps-hd-hevc.mkv':0/0
  Metadata:
    COMPATIBLE_BRANDS: iso4hvc1iso6
    MAJOR_BRAND     : iso4
    MINOR_VERSION   : 1
    ENCODER         : Lavf56.3.100
  Duration: 00:00:30.10, start: 0.067000, bitrate: 9978 kb/s
    Stream #0:0(und): Video: hevc (Main), yuv420p(tv), 1920x1080 [SAR 1:1
DAR 16:9], 29.97 fps, 29.97 tbr, 1k tbn, 29.97 tbc (default)
    Metadata:
      CREATION_TIME   : 2016-02-04 22:41:00
      LANGUAGE        : und
      HANDLER_NAME    : hevc@GPAC0.5.2-DEV-rev565-g71748d7-ab-suite
[swscaler @ 0xab3e7360] No accelerated colorspace conversion found from
yuv420p to bgra.
X Error of failed request:  GLXBadRenderRequestKB sq=    0B f=0/0
  Major opcode of failed request:  148 (GLX)
  Minor opcode of failed request:  1 (X_GLXRender)
  Serial number of failed request:  311
  Current serial number in output stream:  313
--------------------------------------------------------------------------------------------------

Best regards

On Sun, Jun 10, 2018 at 2:25 AM Moritz Barsnick <[hidden email]> wrote:

> On Sat, Jun 09, 2018 at 21:44:28 +0200, Carl Eugen Hoyos wrote:
> > ffmpeg (the application) supports several audio output
> > devices like alsa, pulse and oss. They may be what
> > you need.
>
> But Mohammed's input video didn't even have an audio stream?
>
> I'm still convinced it's either an ffplay bug, or it's intended.
> "The file contains only audio, and '-an' is given, so refuse to play."
> "The file contains only video, and '-vn'/'-nodisp' is given, so refuse to
> play."
> "The file contains audio and video, and at least one of them isn't
> disabled, so go ahead with decoding."
>
> I'm not sure the video decoder is used with '-vn'/'-nodisp', so perhaps
> running ffplay like this doesn't fulfill Mohammed's cause.
> "ffmpeg -i ... -f null -" may be more effective.
>
> $ ffmpeg -f lavfi -i testsrc -t 10 test.vid.mp4
> $ ffmpeg -f lavfi -i sine -t 10 test.aud.mp4
> $ ffmpeg -f lavfi -i testsrc -f lavfi -i sine -t 10 test.vid+aud.mp4
> $ ffplay -nodisp test.vid+aud.mp4
> $ ffplay -nodisp test.aud.mp4
> $ ffplay -nodisp test.vid.mp4
>
> The last one fails with said error. So does
> $ ffplay -an test.aud.mp4
>
> 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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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Carl Eugen Hoyos-2
2018-06-11 12:47 GMT+02:00, mohammed bey ahmed khernache <[hidden email]>:


> I tried to run *ffplay* without "-*nodisp*" option, where being
> connected to my board via *Remote Desktop Connection*.
> Unfortunately, ffplay couldn't play it.

Did you already try ffmpeg and one of its numerous audio
output devices?

Please remember not to top-post here, Carl Eugen
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Carl Eugen Hoyos-2
In reply to this post by Moritz Barsnick
2018-06-10 2:20 GMT+02:00, Moritz Barsnick <[hidden email]>:
> On Sat, Jun 09, 2018 at 21:44:28 +0200, Carl Eugen Hoyos wrote:
>> ffmpeg (the application) supports several audio output
>> devices like alsa, pulse and oss. They may be what
>> you need.
>
> But Mohammed's input video didn't even have an audio stream?
>
> I'm still convinced it's either an ffplay bug, or it's intended.

Really?

> "The file contains only audio, and '-an' is given, so refuse to play."

Yes.

> "The file contains only video, and '-vn'/'-nodisp' is given, so refuse to
> play."

Yes.

> "The file contains audio and video, and at least one of them isn't disabled,
> so go ahead with decoding."

Yes.

> I'm not sure the video decoder is used with '-vn'/'-nodisp',

It should not be used afaict.

> so perhaps running ffplay like this doesn't fulfill Mohammed's cause.
> "ffmpeg -i ... -f null -" may be more effective.

It is certainly a good idea if he just needs a performance test.

> $ ffmpeg -f lavfi -i testsrc -t 10 test.vid.mp4
> $ ffmpeg -f lavfi -i sine -t 10 test.aud.mp4
> $ ffmpeg -f lavfi -i testsrc -f lavfi -i sine -t 10 test.vid+aud.mp4
> $ ffplay -nodisp test.vid+aud.mp4
> $ ffplay -nodisp test.aud.mp4

These work as expected afaict.

> $ ffplay -nodisp test.vid.mp4

This can only fail afaict (and it does).

What do I misunderstand?

Carl Eugen
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Carl Eugen Hoyos-2
In reply to this post by mohammed bey ahmed khernache
2018-06-07 23:40 GMT+02:00, mohammed bey ahmed khernache <[hidden email]>:

> My purpose is to calculate some metrics such as: fps, miss rate, etc, of
> video decoding. So I need only to decode a video without displaying it.

Sorry for missing this:
In this case, ffplay is the wrong tool for you, ffmpeg -i input -an -f null -
may be a better idea.

Carl Eugen
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Moritz Barsnick
In reply to this post by Carl Eugen Hoyos-2
On Mon, Jun 11, 2018 at 23:31:33 +0200, Carl Eugen Hoyos wrote:
> > I'm still convinced it's either an ffplay bug, or it's intended.
> Really?

Yes. What are you implying with your question? That the behavior is
neither a bug nor is it the way ffplay was intended to behave? (Do you
not understand "or", or do you not understand "intended"?)

*I* was trying to say: If Mohammed's expectation was correct - I did
follow it for a while - then it's some sort of bug. OTOH, if this
behavior was intended, then it's obviously correct. Perhaps I should
have written: "I'm not sure this is the intended behavior." (I am now.)

(By the way, I was truly misled by the fact that I found no audio
"equivalent" of "-nodisp", and thought it implied "don't play, just
decode", when in fact it's an alias for "-vn" and the equivalent is
"-an".)

> > $ ffplay -nodisp test.aud.mp4
>
> These work as expected afaict.
>
> > $ ffplay -nodisp test.vid.mp4
>
> This can only fail afaict (and it does).

Then does it not also "work" as expected?

I find ffplay's error message misleading, but "patch surely welcome,
but no patch attached".

Moritz
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Carl Eugen Hoyos-2
2018-06-11 23:50 GMT+02:00, Moritz Barsnick <[hidden email]>:
> On Mon, Jun 11, 2018 at 23:31:33 +0200, Carl Eugen Hoyos wrote:
>> > I'm still convinced it's either an ffplay bug, or it's intended.
>>
>> Really?
>
> Yes. What are you implying with your question?

That tautologies are typically true.

Carl Eugen
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

Zak
In reply to this post by Carl Eugen Hoyos-2
On 2018-06-11 at 5:32 PM EDT, Carl Eugen Hoyos wrote:
> 2018-06-07 23:40 GMT+02:00, mohammed bey ahmed khernache <[hidden email]>:
>
>> My purpose is to calculate some metrics such as: fps, miss rate, etc, of
>> video decoding. So I need only to decode a video without displaying it.
>
> Sorry for missing this:
> In this case, ffplay is the wrong tool for you, ffmpeg -i input -an -f null -
> may be a better idea.
>

Okay, I am going to ask the questions that have been on my mind for this
entire thread:

1. What is the goal of the original email? Frames per second is
available from ffprobe, right? Does "miss rate" refer to cache misses
while operating on the compressed video data? Won't the number of cache
misses depend on many factors, possibly including whether the computer
hardware is also busy rendering and displaying a video on the screen,
such that disabling all video display actually will change the "miss
rate"? This does not seem like a characteristic of the video file
itself, it seems like a statistic that is only available during a
specific instance of playing the video with specific software and
hardware. Or maybe I am misunderstanding. The number of cache misses may
in practice be exactly the same every time you play a given video on
certain hardware, but the original email says the test is being run
remotely on a computer that cannot display video, so any actual playback
will occur on a different computer that will have different performance,
unless I am misunderstanding.

2. What does ffmpeg with -f null really do, and how is it different than
ffprobe?

Thank you,

Zak
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Re: why ffplay cannot decode a sequence that can be decoded by ffmpeg

mohammed bey ahmed khernache
>  In this case, ffplay is the wrong tool for you, ffmpeg -i input -an -f
null -
> may be a better idea.
FFmpeg decodes a video depending on the hardware capacities, i.e., a video
of 10 sec may be decoded in more than 1 mn or in only 5 sec. Therefore,
FFmpeg doesn't incur miss rate (all frames are decoded and no one is
dropped).
To be clear, in my experiments, I want to evaluate video decoding using
FFmpeg while running on multi-core.
*Question:*
Is there a way to decode a video using FFmpeg at a certain fps (e,g,, 25
fps) independently of the hardware capacities (*m**aybe by adding some code
to FFmpeg and rebuilding it*). Of course, we will get different qualities,
i.e., for example using 2 cores we will get 100 dropped frames whereas
using 4 cores we will get only 5 dropped frames.

>  Frames per second is
> available from ffprobe, right?
Yes, it gives the fps at which it is encoded. In my experiments, I need the
fps while decoding the video. It is different because it depends on the
hardware performance.
>  -f null /dev/null
as I understood, this parameter allows to throw the decoded frames, i.e.,
the decoded frames are lost.

‚ÄčThank you again for all your replies.‚Äč


On Tue, Jun 12, 2018 at 3:27 AM Zak <[hidden email]> wrote:

> On 2018-06-11 at 5:32 PM EDT, Carl Eugen Hoyos wrote:
> > 2018-06-07 23:40 GMT+02:00, mohammed bey ahmed khernache <
> [hidden email]>:
> >
> >> My purpose is to calculate some metrics such as: fps, miss rate, etc, of
> >> video decoding. So I need only to decode a video without displaying it.
> >
> > Sorry for missing this:
> > In this case, ffplay is the wrong tool for you, ffmpeg -i input -an -f
> null -
> > may be a better idea.
> >
>
> Okay, I am going to ask the questions that have been on my mind for this
> entire thread:
>
> 1. What is the goal of the original email? Frames per second is
> available from ffprobe, right? Does "miss rate" refer to cache misses
> while operating on the compressed video data? Won't the number of cache
> misses depend on many factors, possibly including whether the computer
> hardware is also busy rendering and displaying a video on the screen,
> such that disabling all video display actually will change the "miss
> rate"? This does not seem like a characteristic of the video file
> itself, it seems like a statistic that is only available during a
> specific instance of playing the video with specific software and
> hardware. Or maybe I am misunderstanding. The number of cache misses may
> in practice be exactly the same every time you play a given video on
> certain hardware, but the original email says the test is being run
> remotely on a computer that cannot display video, so any actual playback
> will occur on a different computer that will have different performance,
> unless I am misunderstanding.
>
> 2. What does ffmpeg with -f null really do, and how is it different than
> ffprobe?
>
> Thank you,
>
> Zak
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>
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> [hidden email] with subject "unsubscribe".
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