[Mplayer-cvslog] CVS: main/DOCS/tech mpcf.txt,1.7,1.8

[Andreas Hess]

On Fri, Feb 07, 2003 at 04:58:42PM +0100, Michael Niedermayer wrote:
> > Ok, I see, but what about making the checksum forward calculated?
> u mean storing the checksum for the future frames ...
> seems difficult, for write only stuff like realtime streaming we cant write te 
> checksum later into the previous keyframe, and i dont see any advantage in 
> this even if its possible, so iam against it unless u have some example where 
> it would provide an advantage

The intention behind storing the checksum just in keyframes is to
keep the frames as simple as possible. No exceptions like, the last
frame before a keyframe has to have a checksum and things like that.
The question regarding your example with realtime streaming is,
has a checksum there any worth? What if the checksum doesn't match,
retransmitting the frame (or the sequence of frames) isn't a
possibility, it's _realtime_ streaming ;) . So if the checksum
doesn't match, the only chance you have with realtime streaming
is drop the frame, but on the other hand, you can't drop frames,
you've already played ;)

So what is the purpose of the checksum? IMHO the only purpose is to
know that something went wrong while downloading or editing your
video. So a checksum in every keyframe should be enough. If you have
keyframes with a checksum every 3 seconds or if you have frames with
a checksum maybe every 1.5 seconds, IMHO there isn't a big difference 
between downloading 3 or 1.5 new seconds.


[...]


Andreas