[FFmpeg-trac] #4901(undetermined:closed): mjpeg codec ignores -threads 1

FFmpeg trac at avcodec.org
Fri Oct 2 17:09:12 CEST 2015


#4901: mjpeg codec ignores -threads 1
-------------------------------------+-------------------------------------
             Reporter:  jvd66        |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:  invalid
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------

Comment (by jvd66):

 Problem fixed temporarily with patch to ffmpeg.c version 2.2.16 :

 {{{
 --- ffmpeg.c~   2015-06-18 18:55:40.000000000 +0000
 +++ ffmpeg.c    2015-10-02 14:58:55.153062041 +0000
 @@ -2167 +2167,2 @@
 -        if (!av_dict_get(ist->opts, "threads", NULL, 0))
 +        if ((!ist->st->codec->thread_count) &&
 +            !av_dict_get(ist->opts, "threads", NULL, 0))
 @@ -2355,0 +2357,3 @@
 +        if( codec && icodec && codec->thread_count && !
 icodec->thread_count )
 +            icodec->thread_count = codec->thread_count;
 +
 }}}

 At least this now prevents ffmpeg spawning 8 threads to process input
 stream:

 {{{
    $ strace -e trace=clone ./ffmpeg  -i a_video.avi -threads 1  -vf null
 -af null -f mjpeg  -vframes 1 -ss 00:00:10.000 -an -y a_video.jpg 2>&1 |
 grep clone
    $
    # no output - no threads cloned.
 }}}

 But, alas the performance is still terrible WRT to 0.8.5 :
 {{{
    $ ./ffmpeg -i a_video.avi -threads 1 -vf null -af null -f mjpeg
 -vframes 1 -ss 00:00:10.000 -an -y a_video.jpg
    [elapsed]=0.206965 [cpu%]=99.72 [sys]=0.006971 [user]=0.199424
 [rss]=20744 [csw]=1 [vcsw]=273 [fltmaj]=0 [fltmin]=4471 [inblk]=0
 [outblk]=0 [exit]=0

 }}}

 Now

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Ticket URL: <https://trac.ffmpeg.org/ticket/4901#comment:5>
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