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=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 http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
