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<DIV id=IncrediOriginalMessage><I>-------Original Message-------</I></DIV>
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<DIV dir=ltr style="FONT-SIZE: 11pt" <i><B>From:</B></I> <A href="mailto:x264-devel@videolan.org">x264-devel@videolan.org</A></DIV>
<DIV dir=ltr style="FONT-SIZE: 11pt" <i><B>Date:</B></I> 01/17/07 07:41:30</DIV>
<DIV dir=ltr style="FONT-SIZE: 11pt" <i><B>To:</B></I> <A href="mailto:x264-devel@videolan.org">x264-devel@videolan.org</A></DIV>
<DIV dir=ltr style="FONT-SIZE: 11pt" <i><B>Subject:</B></I> [x264-devel] Re: AW: Re: Slices in x264</DIV></DIV>
<DIV> </DIV>
<DIV>On Wednesday 17 January 2007 12:30, List, Peter wrote:</DIV>
<DIV>> > -----Ursprüngliche Nachricht-----</DIV>
<DIV>> > Von: <A href="mailto:x264-devel-bounce@videolan.org">x264-devel-bounce@videolan.org</A> [mailto:x264-devel-</DIV>
<DIV>> > <A href="mailto:bounce@videolan.org">bounce@videolan.org</A>] Im Auftrag von Tobias Bergmann</DIV>
<DIV>> > Gesendet: Mittwoch, 17. Januar 2007 11:17</DIV>
<DIV>> > An: <A href="mailto:x264-devel@videolan.org">x264-devel@videolan.org</A></DIV>
<DIV>> > Betreff: [x264-devel] Re: Slices in x264</DIV>
<DIV>> ></DIV>
<DIV>> > Guillaume Poirier wrote:</DIV>
<DIV>> > > Måns Rullgård wrote:</DIV>
<DIV>> > >> Guillaume Poirier <<A href="mailto:gpoirier@mplayerhq.hu">gpoirier@mplayerhq.hu</A>> writes:</DIV>
<DIV>> > >> Using error correcting coding at the transmission layer</DIV>
<DIV>> > >> substantially increases the bitrate. With slices a transmission</DIV>
<DIV>> > >> error will ruin the rest of the slice, while other slices still</DIV>
<DIV>> > >> decode properly. Sometimes a little damage here and there is</DIV>
<DIV>> > >> acceptable if it means you can keep the bitrate down. Besides, you</DIV>
<DIV>> > >> don't always have control over the transmission encoding.</DIV>
<DIV>> > >></DIV>
<DIV>> > >> Put another way, slices limit the scope of the damage caused by</DIV>
<DIV>> > >> whatever transmission errors make it through your error correction</DIV>
<DIV>> > >> layers.</DIV>
<DIV>> > >></DIV>
<DIV>> > >> Anyone who has watched digital TV should appreciate the usefulness</DIV>
<DIV>> > >> of slices.</DIV>
<DIV>> > ></DIV>
<DIV>> > > Mmmm. I guess I did not understand what "error concealment" meant. My</DIV>
<DIV>> > > dictionary translates it to "dissimulation des erreurs" which more or</DIV>
<DIV>> > > less translates back in English as "error hiding", which by my book</DIV>
<DIV>> > > means that if an error occurs, it doesn't show, up to a certain</DIV>
<DIV>> > > amount of errors you can't recover.</DIV>
<DIV>> > ></DIV>
<DIV>> > > As far as I understand, slices don't allow that, that's why I thought</DIV>
<DIV>> > > that better error correction blocks was the solution.</DIV>
<DIV>> > ></DIV>
<DIV>> > > But now that I understand what "error concealment" means, and I see</DIV>
<DIV>> > > that slices seem like the right tool for that job.</DIV>
<DIV>> > ></DIV>
<DIV>> > > Sorry for the trouble. I'm learning smth new every day :-)</DIV>
<DIV>> ></DIV>
<DIV>> > What slices support as-is is spatial "error containment". Together with</DIV>
<DIV>> > a defined I frame interval (or at least intra-mb interval) temporal</DIV>
<DIV>> > "error containment" is provided as well.</DIV>
<DIV>> ></DIV>
<DIV>> > If I get it right, the new method tries to "fix" parts of the broken</DIV>
<DIV>> > stream based on surrounding motion vectors. That could be called "error</DIV>
<DIV>> > concealment" but has nothing to do with slices.</DIV>
<DIV>> ></DIV>
<DIV>> > A better tool instead of slices is that completely coded macroblock</DIV>
<DIV>> > which resets the stream. It can be placed as often as needed depending</DIV>
<DIV>> > on current line quality (if there is a feedback on that).</DIV>
<DIV>></DIV>
<DIV>> I guess by "completely coded" you mean Intra coded macroblocks. The</DIV>
<DIV>> problem here is that artefacts due to bitstream errors usually get</DIV>
<DIV>> smeared over the whole picture. In other words you can not fix one wrong</DIV>
<DIV>> macroblock with one correct intra-macroblock. Errors DON'T get smeared</DIV>
<DIV>> over slice boundaries though. An Intra-Slice once in a while DOES fix the</DIV>
<DIV>> problem for that slice!</DIV>
<DIV> </DIV>
<DIV>Errors do get smeared over slice boundaries in subsequence pictures that use</DIV>
<DIV>the error picture for reference. There is no clause that states that motion</DIV>
<DIV>vectors cannot cross slice boundaries in the picture that they are</DIV>
<DIV>referencing. So to force update using an intra slice in any picture after</DIV>
<DIV>the next one in decoding order you need to determine how much the error</DIV>
<DIV>could have travelled. This gets quite complicated I would imagine.</DIV>
<DIV> </DIV>
<DIV>Of course, you could design the encoder to use the same fixed arrangement of</DIV>
<DIV>slices in every picture and not cross those slice boundaries with motion</DIV>
<DIV>vectors. That would make the forced update as simple as you describe. But</DIV>
<DIV>you would lose the ability to create slices that fit efficiently into a</DIV>
<DIV>single network packet and you would lose some coding efficiency, possibly</DIV>
<DIV>quite a lot.</DIV>
<DIV> </DIV>
<DIV>Cheers,</DIV>
<DIV>-Ryan</DIV>
<DIV> </DIV>
<DIV>--</DIV>
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