[Ffmpeg-devel] [Bad news]: MPEG Seek has failed to work in FFmpeg SVN

[Steve Lhomme]

Michael Niedermayer wrote:
> Hi
> 
> On Fri, Nov 03, 2006 at 06:02:34PM +0100, Steve Lhomme wrote:
>> M?ns Rullg?rd wrote:
>>> Steve Lhomme said:
>>>> M?ns Rullg?rd wrote:
>>>>> Steve Lhomme said:
>>>>>> QuickTime wrote:
>>>>>>> Dear:
>>>>>> Hi Quicktime,
>>>>>>
>>>>>>> FFmpeg fails to decode video(avcodec_decode_video() never return
>>>>>>> picture) after perform SEEK on mpeg file format
>>>>>>>
>>>>>>> It seems that the seek&decode abiliity for mpeg files have been broken
>>>>>>> for 2 months(ealier than August )
>>>>>>>
>>>>>>> ffmpeg  -ss 00:00:10 -i test.mpg  -r 25 test.mp4
>>>>>>> .....
>>>>>>> Input #0, mpeg, from 'test.mpg':
>>>>>>> Duration: 00:00:24.0, start: 0.346711, bitrate: 2314 kb/s
>>>>>>> Stream #0.0[0x1e0]: Video: mpeg1video, yuv420p, 352x288, 2000 kb/s,
>>>>>>> 25.00 fps(r)
>>>>>>> Stream #0.1[0x1c0]: Audio: mp2, 44100 Hz, stereo, 192 kb/s
>>>>>>> Output #0, mp4, to 'test.mp4':
>>>>>>> Stream #0.0: Video: mpeg4, yuv420p, 352x288, q=2-31, 200 kb/s, 25.00
>>>>>>> fps(c)
>>>>>>> Stream #0.1: Audio: aac, 44100 Hz, stereo, 64 kb/s
>>>>>>> Stream mapping:
>>>>>>> Stream #0.0 -> #0.0
>>>>>>> Stream #0.1 -> #0.1
>>>>>>> frame=    0 q=0.0 Lsize=     120kB time=14.8 bitrate=  66.1kbits/s
>>>>>>> video:0kB audio:114kB global headers:0kB muxing overhead 4.833664%
>>>>>>> .....
>>>>>> I've had similar problems (actually crashes) with some MPEG2 samples
>>>>>> (from DVDs) for a long time. Maybe if you can provide a sample and say
>>>>>> what platform you use, it could help.
>>>>> Yeah, if Steve hadn't refused to provide samples, maybe this had been 
>>>>> fixed
>>>>> already.
>>>> Look at the message "Re: [Ffmpeg-devel] MPEG2 decoding problems" from
>>>> 2006-03-02 there is a chems1.vob sample. The URL should still work.
>>> I have a copy of the file.
>>>
>>>> It was not fixed because you need to seek at a specific place in the
>>>> file to crash. Maybe you can manage to do that by doing a
>>>> forward/backward seek in ffplay during a specific fraction of second
>>>> during playback. I proposed to modify ffplay to test it but it was
>>>> rejected...
>>> We do not support modified versions of ffmpeg.  If this is really a bug in
>>> our code (and caused by your mods), it should be possible to trigger it by
>>> cutting that file of yours in the right spot.  Find this spot, and we'll
>>> look into it.  You can't expect us to do all the work.
>> I tried it. Unfortunately it not as simple as you write it. Our code 
>> uses AVSEEK_FLAG_BYTE when seeking in VOB files (since the timestamps 
>> may not be contiguous/accurate throughout the file). And neither 
>> ffmpeg.c nor ffplay.c use this flag to seek.
> 
> why dont you add AVSEEK_FLAG_BYTE support to ffmpeg/ffplay? maybe with
> a AVFMT_DISCONTINUOS_AKA_USELESS_TIMESTAMPS in AVOutputFormat.flags which
> selects that then by default for such formats

OK, I only added the possibility in ffplay to seek by bytes instead of 
time. Now you can play chems1.vob, seek back a few times and it will 
crash (on MinGW at least). It doesn't with our custom patch that was 
discussed a long time ago as a non valid/clean solution.

$ ./ffplay.exe -bytes /C/test/DivX/chems1.vob

Steve