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

[Michael Niedermayer]

Hi

On Friday 07 February 2003 17:56, Andreas Hess wrote:
> 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 ;)
yes ... no .... :) 
just imagine that ur saving the thing to disk, and other ppl watch the same 
stream & save it too, if u have checksums u can fix the stream by exchangeing 
a few data packets with the other person ...

>
> 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.
and "normal" videos have 10sec between keyframes, at 650mb per file & 90min 
thats 1.2mb, yes its tiny for any decent internet connection but there might 
be many damages and the connection might be less then decent, so imho we 
should keep the current way, perhaps with a recommandition that the crc 
should be stored every 64kb or so ...

[...]

Michael