On Tuesday, January 31, 2017, Chris Cunningham <chcunning...@chromium.org> wrote:
> > On Tue, Jan 31, 2017 at 1:07 AM, wm4 <nfx...@googlemail.com > <javascript:_e(%7B%7D,'cvml','nfx...@googlemail.com');>> wrote: > >> On Tue, 31 Jan 2017 09:57:24 +0100 >> wm4 <nfx...@googlemail.com >> <javascript:_e(%7B%7D,'cvml','nfx...@googlemail.com');>> wrote: >> >> > On Mon, 30 Jan 2017 17:05:49 -0800 >> > Chris Cunningham <chcunning...@chromium.org >> <javascript:_e(%7B%7D,'cvml','chcunning...@chromium.org');>> wrote: >> > >> > > Blocks are marked as key frames whenever the "reference" field is >> > > zero. This is incorrect for non-keyframe Blocks that take a refernce >> > > on a keyframe at time zero. >> > > >> > > Now using -1 to denote "no reference". >> > > >> > > Reported to chromium at http://crbug.com/497889 (contains sample) >> > > --- >> > > libavformat/matroskadec.c | 9 ++++++--- >> > > 1 file changed, 6 insertions(+), 3 deletions(-) >> > > >> > > diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c >> > > index e6737a70b2..0d033b574c 100644 >> > > --- a/libavformat/matroskadec.c >> > > +++ b/libavformat/matroskadec.c >> > > @@ -89,6 +89,7 @@ typedef const struct EbmlSyntax { >> > > int list_elem_size; >> > > int data_offset; >> > > union { >> > > + int64_t i; >> > > uint64_t u; >> > > double f; >> > > const char *s; >> > > @@ -696,7 +697,7 @@ static const EbmlSyntax matroska_blockgroup[] = { >> > > { MATROSKA_ID_SIMPLEBLOCK, EBML_BIN, 0, >> offsetof(MatroskaBlock, bin) }, >> > > { MATROSKA_ID_BLOCKDURATION, EBML_UINT, 0, >> offsetof(MatroskaBlock, duration) }, >> > > { MATROSKA_ID_DISCARDPADDING, EBML_SINT, 0, >> offsetof(MatroskaBlock, discard_padding) }, >> > > - { MATROSKA_ID_BLOCKREFERENCE, EBML_SINT, 0, >> offsetof(MatroskaBlock, reference) }, >> > > + { MATROSKA_ID_BLOCKREFERENCE, EBML_SINT, 0, >> offsetof(MatroskaBlock, reference), { .i = -1 } }, >> > > { MATROSKA_ID_CODECSTATE, EBML_NONE }, >> > > { 1, EBML_UINT, 0, >> offsetof(MatroskaBlock, non_simple), { .u = 1 } }, >> > > { 0 } >> > > @@ -1071,6 +1072,8 @@ static int ebml_parse_nest(MatroskaDemuxContext >> *matroska, EbmlSyntax *syntax, >> > > >> > > for (i = 0; syntax[i].id; i++) >> > > switch (syntax[i].type) { >> > > + case EBML_SINT: >> > > + *(int64_t *) ((char *) data + syntax[i].data_offset) = >> syntax[i].def.i; >> > > case EBML_UINT: >> > >> > Isn't there a break missing? >> > >> > > *(uint64_t *) ((char *) data + syntax[i].data_offset) = >> syntax[i].def.u; >> > > break; >> > > @@ -3361,7 +3364,7 @@ static int >> > > matroska_parse_cluster_incremental(MatroskaDemuxContext >> *matroska) >> > > matroska->current_cluster_num_blocks = blocks_list->nb_elem; >> > > i = blocks_list->nb_elem >> - 1; >> > > if (blocks[i].bin.size > 0 && blocks[i].bin.data) { >> > > - int is_keyframe = blocks[i].non_simple ? >> !blocks[i].reference : -1; >> > > + int is_keyframe = blocks[i].non_simple ? >> blocks[i].reference == -1 : -1; >> > > uint8_t* additional = blocks[i].additional.size > 0 ? >> > > blocks[i].additional.data : NULL; >> > > if (!blocks[i].non_simple) >> > > @@ -3399,7 +3402,7 @@ static int >> > > matroska_parse_cluster(MatroskaDemuxContext >> *matroska) >> > > blocks = blocks_list->elem; >> > > for (i = 0; i < blocks_list->nb_elem; i++) >> > > if (blocks[i].bin.size > 0 && blocks[i].bin.data) { >> > > - int is_keyframe = blocks[i].non_simple ? >> !blocks[i].reference : -1; >> > > + int is_keyframe = blocks[i].non_simple ? >> blocks[i].reference == -1 : -1; >> > > res = matroska_parse_block(matroska, blocks[i].bin.data, >> > > blocks[i].bin.size, >> blocks[i].bin.pos, >> > > cluster.timecode, >> blocks[i].duration, >> > >> > I don't quite trust this. The file has negative block references too >> > (what do they even mean?). E.g. one block uses "-123". This doesn't >> > make much sense to me, and at the very least it means -1 is not a safe >> > dummy value (because negative values don't mean non-keyframe according >> > to your patch, while -1 as exception does). >> > >> > The oldest/most used (until recently at least) mkv demuxer, Haali >> > actually does every block reference element as a non-keyframe: >> > >> > http://git.1f0.de/gitweb?p=ffmpeg.git;a=blob;f=libavformat/ >> MatroskaParser.c;h=173c2e1c20da59d4cf0b501639c470331cd4515f;hb=HEAD#l2354 >> > >> > This seems much safer. >> > >> > Do you have any insight why the file contains such erratic seeming >> > reference values? I'm sure I'm missing something. Or is it a broken >> > muxer/broken file? >> >> Oh, nevermind. The values in the reference elements are >> supposed to be _relative_ timestamps. This means -1 is still not a safe >> dummy value. But then, what is a value of "0" supposed to mean? >> >> Going after Haali seems the safest fix, as it most likely won't break >> anything. >> _______________________________________________ >> ffmpeg-devel mailing list >> ffmpeg-devel@ffmpeg.org >> <javascript:_e(%7B%7D,'cvml','ffmpeg-devel@ffmpeg.org');> >> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel >> > > Thanks for taking a look. > > Definitely missing a "break;" - will fix in subsequent patch. > > Agree timestamps should be relative (didn't realize this). Vignesh points > out that "0" in the test file is due to a bug in ffmpeg (and probably other > muxers) where this value is not written as a relative timestamp, but > instead as the timestamp of the previous frame. https://github.com/FFmp > eg/FFmpeg/blob/master/libavformat/matroskaenc.c#L2053 > <https://www.google.com/url?q=https%3A%2F%2Fgithub.com%2FFFmpeg%2FFFmpeg%2Fblob%2Fmaster%2Flibavformat%2Fmatroskaenc.c%23L2053&sa=D&sntz=1&usg=AFQjCNGs8m6GsWbhTvCZl0Q_juGAldQblA> > . > > Anyway, I'm all for following Haali. Its not obvious how best to do this. > I don't think there's any great default value to indicate "not-set" and the > generic embl parsing code that reads the reference timestamp doesn't really > lend itself to setting an additional field like > MatroskaBlock.has_reference. I can sort this out, but I'll pause in case > you have a recommendation in-mind. > Actually, would it work to just use INT_MIN instead of -1? _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
