On Fri, Jul 26, 2024 at 2:29 PM Michael Niedermayer <mich...@niedermayer.cc> wrote: > > On Thu, Jul 25, 2024 at 05:06:04PM -0700, Pierre-Anthony Lemieux wrote: > > On Thu, Jul 25, 2024 at 2:17 AM Tomas Härdin <g...@haerdin.se> wrote: > > > > > > sön 2024-07-21 klockan 14:07 +0900 skrev Pierre-Anthony Lemieux: > > > > On Sat, Jul 20, 2024 at 5:12 PM Tomas Härdin <g...@haerdin.se> wrote: > > > > > > > > > > tor 2024-07-18 klockan 23:10 +0900 skrev Pierre-Anthony Lemieux: > > > > > > On Mon, Jul 15, 2024 at 10:33 PM Tomas Härdin <g...@haerdin.se> > > > > > > wrote: > > > > > > > > > > > > > > fre 2024-07-12 klockan 12:51 -0700 skrev Pierre-Anthony > > > > > > > Lemieux: > > > > > > > > On Thu, Jul 11, 2024 at 10:28 PM Tomas Härdin > > > > > > > > <g...@haerdin.se> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > + if (s->in_tile_headers == 1 && s->isHT && > > > > > > > > > > (!s- > > > > > > > > > > > Ccap15_b11)) > > > > > > > > > > + av_log(s->avctx, AV_LOG_WARNING, "COD > > > > > > > > > > marker > > > > > > > > > > is > > > > > > > > > > found in HOMOGENEOUS HT set\n"); > > > > > > > > > > > > > > > > > > How bad is this and the other markers being present in this > > > > > > > > > case? > > > > > > > > > > > > > > > > At the very least, it means that signaling is inconsistent > > > > > > > > within > > > > > > > > the > > > > > > > > codestream since the standard states that: > > > > > > > > """ > > > > > > > > The HOMOGENEOUS set is the set of HTJ2K codestreams where: > > > > > > > > • none of the functional marker segments, e.g., COD, COC, > > > > > > > > RGN, > > > > > > > > QCD, > > > > > > > > QCC, and POC, are present in any > > > > > > > > tile-part header; and > > > > > > > > • no PPT marker segment is present. > > > > > > > > """ > > > > > > > > > > > > > > > > The point of signalling that a codestream is "HOMOGENEOUS" is > > > > > > > > to > > > > > > > > allow > > > > > > > > decoders to configure themselves solely based on information > > > > > > > > retrieved > > > > > > > > entirely from the main header. > > > > > > > > > > > > > > > > Since, AFAIK, FFMPEG does not rely on the HOMOGENEOUS to > > > > > > > > short- > > > > > > > > circuit > > > > > > > > configuration, incorrect HOMOGENEOUS signalling will likely > > > > > > > > not > > > > > > > > impact > > > > > > > > FFMPEG. > > > > > > > > > > > > > > It could happen that information in tile headers contradict > > > > > > > information > > > > > > > in the main header, right? In such a case it sounds like we > > > > > > > can't > > > > > > > be > > > > > > > sure which decode is the correct one. > > > > > > > > > > > > Per the spec, the decoder uses the COD information in tile-parts > > > > > > over > > > > > > the COD information in the header. > > > > > > > > > > > > The issue here is that a decoder, upon seeing HOMOGENEOUS, simply > > > > > > does > > > > > > not bother with looking for COD information in tile-parts, > > > > > > thereby > > > > > > missing critical information. > > > > > > > > > > So it is actually perfectly legal? Then it seems this patch is > > > > > wrong > > > > > > > > What is not "illegal": the HOMOGENEOUS flag being equal to true *and* > > > > having COD marker segments in tile-parts. > > > > > > > > This is what the patch detects. > > > > > > > > FFMPEG can decode such illegal codestream. Other decoders might not. > > > > > > > > The question is: what should FFMPEG do? Should FFMPEG exit or warn > > > > and continue. > > > > > > If the spec allows it but it's perhaps unadviced then warning about it > > > seems reasonable > > > > (I totally messed up my double negative. Repeat below. Sorry for the > > confusion.) > > > > What is "illegal": the HOMOGENEOUS flag being equal to true *and* > > having COD marker segments in tile-parts. > > > > This is what the patch detects. > > > > FFMPEG can decode such illegal codestream. Other decoders might not. > > > > The question is: what should FFMPEG do? Should FFMPEG exit or warn and > > continue. > > Does such a codestream actually exist ? I mean is this just a hypothetical > case > or something existing ?
Such a codestream exists: a codestream with the HOMOGENEOUS flag equal to true *and* COD marker segments in tile-parts is "illegal" per the specification. Such a codestream may cause certain decoders (esp. hardware decoders) to fail because, based on the value of the HOMOGENEOUS flag, they will not expect COD marker segments in tile-parts. FFMPEG will not fail, because it does not use the value of the HOMOGENEOUS flag to configure itself. > > thx > > [...] > -- > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB > > Rewriting code that is poorly written but fully understood is good. > Rewriting code that one doesnt understand is a sign that one is less smart > than the original author, trying to rewrite it will not make it better. > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
