[MEncoder-users] Mencoder does not cut exactly

[belcampo]

BUIRA Etienne wrote:
> On Wed, Apr 30, 2008 at 02:35:43PM +0200, TAJTHY Tammms wrote:
>> Hi,
>>
>> I have a strange problem. I have a mjpeg avi file and I'd like to cut a part
>> from it and convert to mpeg4. I detected the frames by VirtualDub. I did the
>> following:
>>
>> mencoder ..compression-arguments.. -ss 1.120 -endpos 1:23:00.000 -o cut.avi
>> patch.avi;
>>
>> My problem is that the resulted file does not contain the exact frames.
>> Depending on the -ss option it can be +/-1 frames different. At the end
>> position can be +/- 4 frames different. If I add 3-5 ms to the -ss and
>> -endpos options so the start become puntual, but the problem still appears
>> at the end.
> 
> Hi.
> 
> The -ss and -endpos method is quite inacurrate (even if you got a very
> good accuracy for using those IMHO...).
> 
> You'd better use -hr-edl-seek, after selecting good timestamps using
> -edlout. From the manpage: See http://www.mplayerhq.hu/DOCS/HTML/en/edl.html
> for details.
> 
> (Sorry if this message appears twice, I messed up again with my email @)
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video and audio are always off by ... msecs, sometimes earlier, 
sometimes later, depending on source.
If sound is off by say .4 sec. then 1 video frame will be added. So I 
think that if you want to be frame-accurate, you'll need to decode video 
and audio separate. You'll have to start at an I-frame till another 
I-frame, not including it.