[x264-devel] Re: H.264 (over MPEG2-TS) over packet-lossy networks

[Alex Izvorski]

On Fri, 2007-02-16 at 23:36 +0100, Michael Niedermayer wrote:
> Hi
> 
> On Tue, Feb 13, 2007 at 01:11:05PM -0800, Alex Izvorski wrote:
> > * you could tweak the decoder you're using to replace a lost slice with
> > the same image data as in the previous picture (optionally shifted by
> > the previous picture's motion vectors).
> 
> as the author said he uses libavcodec, that isnt needed as lavc already
> performs more advanced error concealment (if theres any problem with it
> send us a bugreport ...)

Could you describe how lavc error concealment works?

> [...]
> > * you could calculate checksums in pes packets, and check them on the
> > receiving end.  pretty sure the ffmpeg's ts packetizer/depacketizer
> > doesn't handle that now.  one tricky detail is that checksums for each
> > packet are sent in the header of the next packet with that pid.
> 
> i hope you are aware that these checksums are not intended to be used
> like that (mpeg ts spec: "This CRC is intended for use in network 
> maintenance such as isolating the source of intermittent errors.") if 
> you really have bit errors then you should do some real FEC
> 
> [...]

Absolutely, I meant checksums for detecting errors, not for correcting
them of course.  The reason why I suggest that is that sometimes the pes
packet has no size in the header field, and so you don't absolutely know
if you have all of it or if some parts are missing.  The transport
stream continuity counters are not a reliable way of doing that ;)

--Alex


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