On Tue, Jan 31, 2017 at 1:07 AM, wm4 <nfx...@googlemail.com> wrote: > On Tue, 31 Jan 2017 09:57:24 +0100 > wm4 <nfx...@googlemail.com> wrote: > > > On Mon, 30 Jan 2017 17:05:49 -0800 > > Chris Cunningham <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=173c2e1c20da59d4cf0b501639c470 > 331cd4515f;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 > 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. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
