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

[Michael Niedermayer]

Hi

On Tue, Feb 13, 2007 at 01:11:05PM -0800, Alex Izvorski wrote:
> On Tue, 2007-02-13 at 19:42 +0100, Gonzalo Berdeal wrote:
> > Hello everybody,
> > 
> > I am currently developing a packetizer and depacketizer of H.264 over
> > TS.  For this task I have the Amendment 3 of MPEG-2 Systems.
> > I am using ffmpeg/libavcodec for coding and decoding to H.264 (coding
> > is actually done by x264).
> > 
> > Once done the transmission the depacketizer will have as an input the
> > TS packets, but eventually some packets may have been lost (due to UDP
> > protocol) or may have some bit errors (wireless).
> > Does anybody have any sugestion about how to handle these problems?
> > For example, if the continuity_counter of the TS packets has a
> > discontinuity, may be I could send to the decoder the last error-safe
> > received Slice (frame).
> > 
> > Could anybody give me some ideas?
> > Does anybody know some good references on this topic?
> > 
> > Thank you very much in advance.
> > 
> > Gonzalo Berdeal.
> 
> Hello,
> 
> Yes, a few random ideas...
> 
[...]
> 
> * 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 ...)


[...]
> * 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

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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