[vdr] VDR File splitting validation

Udo Richter udo_richter at gmx.de
Tue Sep 4 22:55:51 CEST 2012


Am 04.09.2012 15:22, schrieb Rares Pop:
> Now, when VDR does the file split (after the quota has been met and a
> video I-Frame is about to start) the audio packets that would be in
> sync with the latest video frames before the split are actually being
> contained in the next split file.

Thats because VDR does splitting and editing on the data stream level, 
not on the audio/video-track level. Merging all the file pieces together 
always gives the original stream, with just very minor modifications.

Editing based on time stamps would be a lot more difficult, as near the 
splitting point, data needs to be moved to the previous/next file, 
depending on whether audio is ahead/behind video. To make things more 
complicated, there's no guarantee that together with the I-frame also a 
new audio frame starts at the exact time stamp. For precise editing, an 
audio frame may have to be split and re-compressed.

And for playback, the same applies in reverse: For pre-buffering, the 
A/V-data of the file end and beginning needs to be merged with proper 
offset again. This is all a lot more complicated than just splitting the 
whole data stream as one.

For further processing, its the best to merge continuous stream parts 
into one big file, if the program cannot handle split files on its own. 
If you want to avoid the copying, take a look at vdrnfofs, a virtual 
file system that virtually merges VDR recordings into single mpg files.


Cheers,

Udo



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