[Ffmpeg-devel] ffmpeg hanging when transcoding mpeg4

[Aaron Williams]

Aaron Williams wrote:
> Michael Niedermayer wrote:
>   
>> Hi
>>
>> On Sat, Oct 21, 2006 at 02:32:11AM -0700, Aaron Williams wrote:
>>   
>>     
>>> I am trying to transcode a video for a friend into MPEG2 for use with a
>>> hardware MPEG decoder and am running into problems with FFMPEG stopping
>>> at the same place in the video and consuming all of the CPU.  I seem to
>>> be unable to do any source level debugging with gdb (even when compiled
>>> with -O2 and -g) so I cannot find the source of the hang.  It always
>>> occurs at about time 236.2 in the file.
>>>     
>>>       
>> you do use ffmpeg_g for debugging right?
>> and maybe try valgrind
>>   
>>     
> I do not see ffmpeg_g.  Do I need to do something special in configure
> to build that?  Also, valgrind is reporting problems, but again there
> appears to be no debugging information.
>
> I do see the following though:
> ==20851== Conditional jump or move depends on uninitialised value(s)
> ==20851==    at 0x4DEE61F: ff_mpeg4_decode_mb (in
> /usr/local/lib/libavcodec.so.51.20.0)
> ==20851==    by 0x4DFFB83: (within /usr/local/lib/libavcodec.so.51.20.0)
> ==20851==    by 0x4E00F40: ff_h263_decode_frame (in
> /usr/local/lib/libavcodec.so.51.20.0)
> ==20851==    by 0x4CCF222: avcodec_decode_video (in
> /usr/local/lib/libavcodec.so.51.20.0)
> ==20851==    by 0x40A5D3: (within /usr/local/bin/ffmpeg)
> ==20851==    by 0x40C2C4: main (in /usr/local/bin/ffmpeg)
>
>
> I can get the file to transcode if I scale it to certain resolutions. 
> The source is MPEG4 at 720x380, encoded with an aspect ratio of 16:9. 
> If I scale it to 720x480 it hangs.  If I scale it to 720x352 and add 64
> pixels of padding above and below it works.  It seems to be a bug
> somewhere in the scaling code.  If I convert to h264 instead of mpeg2
> then it seems to go through OK.
>
> I think the original video was improperly scaled for a 16:9 aspect ratio
> as well.
>
> I am trying to cut the size of the source file as well so I can post a
> link to a smaller file, but this is failing as well:
>
> /usr/local/bin/ffmpeg -i DCF-Brick-DivX-high.avi -vcodec copy -acodec
> copy -y -ss 220 -t 30 DCF-Brick3-hang.avi
> FFmpeg version SVN-r6280, Copyright (c) 2000-2006 Fabrice Bellard, et al.
>   configuration:  --enable-libogg --enable-vorbis --enable-faad
> --enable-faac --enable-xvid --enable-x264 --enable-a52 --enable-dts
> --enable-shared --enable-dc1394 --enable-gpl --enable-mp3lame
>   libavutil version: 49.0.1
>   libavcodec version: 51.20.0
>   libavformat version: 50.6.0
>   built on Oct 21 2006 02:51:51, gcc: 4.1.0 (SUSE Linux)
>
> Seems that stream 0 comes from film source: 29.98 (65534/2186) -> 29.97
> (2997/100)
> Input #0, avi, from 'DCF-Brick-DivX-high.avi':
>   Duration: 00:07:09.6, start: 0.000000, bitrate: 865 kb/s
>   Stream #0.0: Video: mpeg4, yuv420p, 720x380, 29.97 fps(r)
>   Stream #0.1: Audio: mp3, 48000 Hz, stereo, 128 kb/s
> Output #0, avi, to 'DCF-Brick3-hang.avi':
>   Stream #0.0: Video: mpeg4, yuv420p, 720x380, q=2-31, 29.98 fps(c)
>   Stream #0.1: Audio: mp3, 48000 Hz, stereo, 128 kb/s
> Stream mapping:
>   Stream #0.0 -> #0.0
>   Stream #0.1 -> #0.1
> Press [q] to stop encoding
> error, non monotone timestamps 9170 >= 9170
> error, non monotone timestamps 9173 >= 9173
> ...
> frame=  900 q=0.0 Lsize=    3589kB time=250.0 bitrate= 117.6kbits/s
> video:3039kB audio:476kB global headers:0kB muxing overhead 2.103378%
>
> -Aaron
>
>
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>
>   
I found the ffmpeg_g and that works a lot better for debugging.
It looks like it is stuck in the MPV_encode_picture where it
continuously goes back to vbv_retry.


(gdb) p s->pb
$3 = {bit_buf = 0, bit_left = 32, buf = 0x2b726eaa4010 "",
  buf_ptr = 0x2b726eab3dba, buf_end = 0x2b726ebf5810 }
(gdb) p s->rc_context.buffer_index
$4 = 1544315
(gdb)                         
(gdb) p s->next_lambda
$5 = 0
(gdb) p s->lambda
$6 = 0
(gdb)  p s->qscale
$7 = 2

It looks like the problem is that s->lambda is zero and will never
scale, hence it gets stuck in an endless loop.

-Aaron