[Ffmpeg-devel] seek with duration for cutting: broken or changed?

[Cyrus A]

Michael Niedermayer wrote:
> Hi
>
> On Mon, Oct 30, 2006 at 05:37:25PM -0500, Cyrus A wrote:
>   
>> Michael Niedermayer wrote:
>>     
>>> Hi
>>>
>>> On Mon, Oct 30, 2006 at 12:55:16PM -0500, Cyrus A wrote:
>>>  
>>>       
>>>> The following command used to work to cut a specific segment out of a 
>>>> video file on some FC3 machines I'm using with an old version of ffmpeg 
>>>> (still does work):
>>>>
>>>> ffmpeg -acodec copy -vcodec copy -i fullvideo.avi -ss 60 -t 120 
>>>> choppedvideo.avi
>>>>
>>>> But it doesn't work anymore with Fedora Core 5 on a 64-bit machine 
>>>> running today's SVN copy of ffmpeg. (Also doesn't work with freshrpms 
>>>> latest ffmpeg rpm, either.) I believe what it's doing is seeking, but 
>>>> the duration is completely ignored. It just returns the rest of the file 
>>>>         
>>> >from where the seek took it. The resulting file is also a little 
>>>       
>>>> "chirpy"  -- the audio video sync is messed up somehow.
>>>>    
>>>>         
>>> could you find out when this problem was introduced into svn (see 
>>> binary search and svn up -r)
>>>
>>> [...]
>>>
>>>  
>>>       
>> Found it. The seek + duration option worked normally through revision 
>> 4526 and then stopped working in 4527 and every other revision 
>> thereafter. It was August 15th, 2005.
>>
>> The change notes read:
>>
>> parse pict_type for streams in avi
>> fix mpeg4 parser so it outputs te pict_type
>> support header only parseing without repacking
>>
>> That's interesting since I'm using mpeg4 for my vcodec and producing an 
>> AVI file.
>>
>> Man, binary searching like that is not fun. Please let me know what you 
>> think.
>>     
>
> i think ive just fixed it ...
>
> [...]
>   
Ok, that helped. The "ffmpeg -i input.avi -acodec copy -vcodec copy -ss 
5 -t 10 output.avi" command no longer churns as before. The cut is very 
quick and look as if it worked. But it doesn't. Here are the various 
commands I used for some tests: ("old" means 0.4.8 ffmpeg-era on 32-bit 
machines):

6849 rec: ffmpeg -i /dev/video0 -async 1 -y -vcodec mpeg4 -acodec mp3 -t 
30 -b 1750k -ab 192 -ar 44100 -s 480x384 test.avi
old rec: ffmpeg -r ntsc -vd /dev/video0 -ad /dev/audio -vcodec mpeg4 
-acodec mp3 -y -s 480x384 -b 1750 -t 30 test.avi

6849 cut: ffmpeg -i test.avi -acodec copy -vcodec copy -y -ss 5 -t 20 
test_cut.avi
old cut: ffmpeg -i test.avi -acodec copy -vcodec copy -y -ss 5 -t 20 
test_cut.avi

6849 cut reenc: ffmpeg -i test.avi -acodec mp3 -vcodec mpeg4 -y -ss 5 -t 
20 test_cut.avi
old cut reenc: ffmpeg -i test.avi -acodec mp3 -vcodec mpeg4 -y -ss 5 -t 
20 test_cut.avi

Here is the 2x3 results table:
               oldcopy            6849copy       6849reenc    <-- cut 
with this version
old          OK                  aud b4 vid      no audio at all
6849     aud b4 vid        *aud b4 vid*      OK
^---- recorded with this version

*= this is the one I need to work

So if I record on the old version and copy-cut with the old version, it 
works. Ditto the 6849 revision when reencode cut with -acodec mp3 and 
vcodec mpeg4. Problem is, the old version won't compile on my 64 bit 
machine under FC5 (common.h: incompat element type) and the new version 
won't do a copy cut. A reencode cut doesn't help me because it takes 
forever for big files. These cuts have to be quick for web application use.

An interesting note I found was that for those that have "audio before 
video" the audio is exactly 5 seconds before the video. So, I tried -ss 
2 and, whammo, the audio was only 2 seconds before the video. Likewise, 
-ss 8 made the audio 8 seconds before the video. Obviously, this is the 
problem.

If anyone can help me get syncd files from a "cut" process, I would 
really really appreciate it.

Cyrus