[FFmpeg-user] issue with concat and seek

Carles Vila cvilad at gmail.com
Wed Oct 19 21:24:20 EEST 2016

Thanks for hinting in the right direction. Indeed there was no key frame up to sec. 10,5 (amazed by this!) The fact that QuickTime player did *not* show the cut beginning increased  my confusion. But further processing with ffmpeg (concat) proves that the frames are there.
Increasing the seek has solved the issue..

-----Mensaje original-----
De: "Cley Faye" <cleyfaye at gmail.com>
Enviado: ‎19/‎10/‎2016 19:43
Para: "FFmpeg user questions" <ffmpeg-user at ffmpeg.org>
Asunto: Re: [FFmpeg-user] issue with concat and seek

2016-10-19 17:51 GMT+02:00 Moritz Barsnick <barsnick at gmx.net>:

> No, ffmpeg should actually cut with "-ss".

​Hmm, I'm not sure. This wiki page (https://trac.ffmpeg.org/wiki/Seeking
) says:
> Using -ss as input option together with -c:v copy might not be accurate
since ffmpeg is forced to only use/split on i-frames. Though it will—if
possible—adjust the start time of the stream to a negative value to
compensate for that. Basically, if you specify "second 157" and there is no
key frame until second 159, it will include two seconds of audio (with no
video) at the start, then will start from the first key frame. So be
careful when splitting and doing codec copy.

To me, it sound like it might copy all the video, and set the stream to
start at the specified time, if there is no keyframe between the start and
the cutting point. If that's the case, then concat might not be honoring
this starting time.
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