[Matroska-users] mkvmerge: fps (default-duration) not set when using .mp4

Christian HJ Wiesner chris at matroska.org
Mon Nov 21 20:33:46 CET 2005

Armin Müller schrieb:

> Hello,
> i want to create matroska files with the mkvmerge application under  
> Linux. My problem is, that the fps (default-duration) are not set in  
> the final .mkv file.
> The source is a .mp4 file with MPEG-4 encoded video. Is it possible  
> to read the fps out of MPEG-4 encoded video? If i use an .avi (with  
> the same source video) the fps are set correctly.
> Is this a big or working as intended? How can i fix this? Should I  
> reencode the files, maybe to an other format?

FPS (default duration) is not mandatory, and normally only added by 
mkvmerge to support simple players like mplayer v1, which requires such 
a value to work correctly, and only for VfW mode MKV files (which is 
what you normally get when muxing an AVI into MKV). When you transmux a 
MP4 into a MKV , the timestamps of the blocks will replace the default 
duration, as MP4 files can be VFR (Variable Framerate) in principal 
(although there is no MP4 muxer/encoder doing that yet). For this 
reason, no default duration is written in the final MKV file.
I have no idea how mplayer is handling this kind of MKV files, as my 
information is it will require such a value. Mosu to answer.

> Btw. Is there an editor for changing/ setting the Matroska values  
> (metadata/ tags) in Linux (after the creation)?
> thanks and best regards, Armin 

not to my knowledge, only app doing that IMO is the matroska shell 
extension matroskaprop.exe for Windows.


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