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demux_mkv: discard broken index 

Add a simplistic heuristic for detecting broken indexes. This includes
indexes with very few elements (apparently libavformat sometimes writes
such indexes, or used to), and indexes with broken timestamps.

The latter was apparently produced by very old HandBrake versions:

| + Muxing application: libmkv 0.6.1.2
| + Writing application: HandBrake 0.9.1

These broken files seem to be common enough that libavformat added a
workaround for them in 2008 (and maybe again in 2015). Apparently all
timestamps are multiplied with the file's tc_scale twice, and FFmpeg
attempts to fix them. We should throw away the whole thing.
This commit is contained in:
wm4 2015-08-26 22:47:07 +02:00
parent dae464a491
commit ba384fffca
1 changed files with 17 additions and 4 deletions
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21
demux/demux_mkv.c
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@ -735,15 +735,25 @@ static int demux_mkv_read_cues(demuxer_t *demuxer)
if (ebml_read_element(s, &parse_ctx, &cues, &ebml_cues_desc) < 0)
return -1;
for (int i = 0; i < cues.n_cue_point; i++) {
struct ebml_cue_point *cuepoint = &cues.cue_point[i];
if (cuepoint->n_cue_time != 1 || !cuepoint->n_cue_track_positions) {
MP_WARN(demuxer, "Malformed CuePoint element\n");
goto done;
}
if (cuepoint->cue_time / 1e9 > mkv_d->duration / mkv_d->tc_scale * 10 &&
mkv_d->duration != 0)
goto done;
}
if (cues.n_cue_point <= 3) // probably too sparse and will just break seeking
goto done;
// Discard incremental index.
mkv_d->num_indexes = 0;
mkv_d->index_has_durations = false;
for (int i = 0; i < cues.n_cue_point; i++) {
struct ebml_cue_point *cuepoint = &cues.cue_point[i];
if (cuepoint->n_cue_time != 1 || !cuepoint->n_cue_track_positions) {
MP_WARN(demuxer, "Malformed CuePoint element\n");
continue;
}
uint64_t time = cuepoint->cue_time;
for (int c = 0; c < cuepoint->n_cue_track_positions; c++) {
struct ebml_cue_track_positions *trackpos =
@ -763,6 +773,9 @@ static int demux_mkv_read_cues(demuxer_t *demuxer)
// Do not attempt to create index on the fly.
mkv_d->index_complete = true;
done:
if (!mkv_d->index_complete)
MP_WARN(demuxer, "Discarding potentially broken or useless index.\n");
talloc_free(parse_ctx.talloc_ctx);
return 0;
}