[vdr] Re: cutting frame accurate?

[Jörg Knitter <joerg.knitter@gmx.de>]

> Frame accurate cutting is too much hassle.
> 
> From one I-Frame to the next I-Frame (on most channels) is 12/25
Second
> (A bit less than 0.5 seconds)
> 
> You would buy this "minimal added value" for a much higher price then
> (at least i) seen in the 11 Frames (worst case) too much.
> 
> Simplified(*) there would be this steps:
> a) Decode Frames
> b) Extract Audio
> c) Cut the Audio according to Picture.
> d) Calculate Offset (=sync between Audio/Video)
> e) Reencode Frames
> f) Remultiplex Audio/Video
> 
> 
> 
> *: I mean simplified!

I recorded StarWars EP4-6, and cutting the commercials out at I frames
caused some visible jumps. When I was able to use frame accurate
cutting, the break would be more seemless IMHO. Imagine a cut at the
last frame of last GOP and the next cut at the very beginning of the
next (not an I frame), then you get a break of nearly one second. To be
honest: This is really the worst case, but possible.

I don´t see any problem syncing audio with video at the beginning of a
commercial break. Split your recording into 2 parts: The part before the
commercial break and the part after.
If you cut only the GOP where the commercial starts, reencode it (frame
accurate up to the point, where the commercial starts) and merge it with
the untouched rest of the first file, DS.JAR just would have to ignore
any timestamp information at the end and continue the audio file just to
the point where the reencoded part ends (up to 12 frames later).
You would make the same with the second file with the difference that
DS.JAR would have to look beyond the reencoded part for timestamps and
then add additional audio frames from the original file at the beginning
with the same length as the reencoded part.
Cuts could be detected by DS.JAR like this: If there is no timestamp in
the MPEG stream, then there is a reencoded part. The next part (the part
after the commercial break) starts at the next I frame, followed by the
untouched video in the next GOP containing time stamps again.

But we would at least need a software that does this frame accurate cut
like M2Edit does...

Jörg




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