On 3/27/2019 12:18 PM, Andreas Rheinhardt via ffmpeg-devel wrote:
The earlier code set the level to zero upon seeking and after a
discontinuity although in both cases parsing (re)starts at a level 1
element.
Also set the segment's length to unkown if an error occured in order not
to drop any valid data that happens to be beyond the designated end of
the segment.
Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@googlemail.com>
---
libavformat/matroskadec.c | 59 +++++++++++++++++++++++----------------
1 file changed, 35 insertions(+), 24 deletions(-)
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 0179e5426e..42f1c21042 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -737,13 +737,24 @@ static const char *const matroska_doctypes[] = { "matroska",
"webm" };
static int matroska_read_close(AVFormatContext *s);
+static int matroska_reset_status(MatroskaDemuxContext *matroska,
+ uint32_t id, int64_t position)
+{
+ matroska->current_id = id;
+ matroska->num_levels = 1;
+ matroska->current_cluster.pos = 0;
+
+ if (position >= 0)
+ return avio_seek(matroska->ctx->pb, position, SEEK_SET);
+
+ return 0;
+}
+
I think you should have done this commit in 2 parts.
- adding matroska_reset_status() and do exactly what was done before
- add changes related to the level and unknown length/discontinuity.
static int matroska_resync(MatroskaDemuxContext *matroska, int64_t last_pos)
{
AVIOContext *pb = matroska->ctx->pb;
int64_t ret;
uint32_t id;
- matroska->current_id = 0;
- matroska->num_levels = 0;
/* seek to next position to resync from */
if ((ret = avio_seek(pb, last_pos + 1, SEEK_SET)) < 0) {
@@ -759,7 +770,14 @@ static int matroska_resync(MatroskaDemuxContext *matroska,
int64_t last_pos)
id == MATROSKA_ID_CUES || id == MATROSKA_ID_TAGS ||
id == MATROSKA_ID_SEEKHEAD || id == MATROSKA_ID_ATTACHMENTS ||
id == MATROSKA_ID_CLUSTER || id == MATROSKA_ID_CHAPTERS) {
- matroska->current_id = id;
+ /* Prepare the context for further parsing of a level 1 element. */
+ matroska_reset_status(matroska, id, -1);
You set num_levels to 1 now, leaving this function used to have
num_levels set to 0. I'm not sure it's correct or not.
+
+ /* Given that we are here means that an error has occured,
I thought this function was meant to find a level1 ID after getting into
a Segment. This does not seem like an error at all.
+ * so treat the segment as unknown length in order not to
+ * discard valid data that happens to be beyond the designated
+ * end of the segment. */
+ matroska->levels[0].length = EBML_UNKNOWN_LENGTH;
return 0;
}
id = (id << 8) | avio_r8(pb);
@@ -1610,18 +1628,12 @@ static int
matroska_parse_seekhead_entry(MatroskaDemuxContext *matroska,
matroska->current_id = 0;
ret = ebml_parse(matroska, matroska_segment, matroska);
-
- /* remove dummy level */
- while (matroska->num_levels) {
- uint64_t length =
matroska->levels[--matroska->num_levels].length;
- if (length == EBML_UNKNOWN_LENGTH)
- break;
- }
I think this code indicates unknown length was handled in a seekhead
entry, probably because such files exist. Making the assumption in 13/21
about unknown length only on Segment+Cluster incorrect.
}
}
- /* seek back */
- avio_seek(matroska->ctx->pb, before_pos, SEEK_SET);
- matroska->current_id = saved_id;
+
+ /* Seek back - notice that in all instances where this is used it is safe
+ * to set the level to 1 and unset the position of the current cluster. */
+ matroska_reset_status(matroska, saved_id, before_pos);
return ret;
}
@@ -3535,9 +3547,7 @@ static int matroska_read_seek(AVFormatContext *s, int
stream_index,
timestamp = FFMAX(timestamp, st->index_entries[0].timestamp);
if ((index = av_index_search_timestamp(st, timestamp, flags)) < 0 || index == st->nb_index_entries - 1) {
- avio_seek(s->pb, st->index_entries[st->nb_index_entries - 1].pos,
- SEEK_SET);
- matroska->current_id = 0;
+ matroska_reset_status(matroska, 0,
st->index_entries[st->nb_index_entries - 1].pos);
while ((index = av_index_search_timestamp(st, timestamp, flags)) < 0 ||
index == st->nb_index_entries - 1) {
matroska_clear_queue(matroska);
if (matroska_parse_cluster(matroska) < 0)
@@ -3557,8 +3567,8 @@ static int matroska_read_seek(AVFormatContext *s, int
stream_index,
tracks[i].end_timecode = 0;
}
- avio_seek(s->pb, st->index_entries[index].pos, SEEK_SET);
- matroska->current_id = 0;
+ /* We seek to a level 1 element, so set the appropriate status. */
+ matroska_reset_status(matroska, 0, st->index_entries[index].pos);
if (flags & AVSEEK_FLAG_ANY) {
st->skip_to_keyframe = 0;
matroska->skip_to_timecode = timestamp;
@@ -3568,18 +3578,16 @@ static int matroska_read_seek(AVFormatContext *s, int
stream_index,
}
matroska->skip_to_keyframe = 1;
matroska->done = 0;
- matroska->num_levels = 0;
ff_update_cur_dts(s, st, st->index_entries[index].timestamp);
return 0;
err:
// slightly hackish but allows proper fallback to
// the generic seeking code.
+ matroska_reset_status(matroska, 0, -1);
matroska_clear_queue(matroska);
- matroska->current_id = 0;
st->skip_to_keyframe =
matroska->skip_to_keyframe = 0;
matroska->done = 0;
- matroska->num_levels = 0;
return -1;
}
@@ -3662,8 +3670,8 @@ static int webm_clusters_start_with_keyframe(AVFormatContext *s)
read = ebml_read_length(matroska, matroska->ctx->pb, &cluster_length);
if (read < 0)
break;
- avio_seek(s->pb, cluster_pos, SEEK_SET);
- matroska->current_id = 0;
+
+ matroska_reset_status(matroska, 0, cluster_pos);
matroska_clear_queue(matroska);
if (matroska_parse_cluster(matroska) < 0 ||
!matroska->queue) {
@@ -3677,7 +3685,10 @@ static int
webm_clusters_start_with_keyframe(AVFormatContext *s)
break;
}
}
- avio_seek(s->pb, before_pos, SEEK_SET);
+
+ /* Restore the status after matroska_read_header: */
+ matroska_reset_status(matroska, MATROSKA_ID_CLUSTER, before_pos);
+
return rv;
}
--
2.19.2
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