[FFmpeg-user] Troubleshooting cat'ing mpeg videos

belcampo belcampo at zonnet.nl
Wed Jul 20 22:47:36 CEST 2011

On 07/20/11 22:25, Brian Cardarella wrote:
> I have two mpg videos that I've transcoded from mp4s. Each are 10
> seconds long. When I play the transcoded mpg files individually they
> run through just fine. But when I cat them into a combined mpg the
> first one plays and when I get to the 10 second mark the 2nd one plays
> for about 2 seconds, wish playback that seems to be skipping frames
> and the audio is off. Then the video ends.
> The combined playing time should be 20 seconds as each file
> individually is 10 seconds. But the combined file only plays for 13
> seconds.
AFAIK it's not possible to cat individual mpeg-files to 1, and expect 
them to play well.
Each individual file has time-stamps, each individual file probably has 
different audio-offsets.
The 'catted' file starts at 0.00 sec and after 10 secs it's reset to 
again 0.00.
If in the first part audio is 1 sec behind video, which will play fine, 
because the player knows how to handle this, and the in the second part 
audio is 1 sec before video, not very common but possible, the player 
gets really confused about what video-frame belongs to what audio.
Demuxing video and audio of both files, then cat these elementary 
streams to 1 video and 1 audio stream, transcode and mux them together 
again. Hope that sync will be correct.
> If it is of any help I have pastied the output from the transocdings
> and an ffprobe of the combined mpg:
> http://pastie.org/2244749
> Any help is greatly appreciated! :)
> - Brian
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