[FFmpeg-devel] [PATCH v2] avformat/mov: add option max_stts_delta
Gyan Doshi
ffmpeg at gyani.pro
Mon Dec 20 10:31:05 EET 2021
Very high stts sample deltas may occasionally be intended but usually
they are written in error or used to store a negative value for dts correction
when treated as signed 32-bit integers.
This option lets the user set an upper limit, beyond which the delta is clamped to 1.
Values greater than the limit if negative when cast to int32 are used to adjust onward dts.
Unit is the track time scale. Default is UINT_MAX - 48000*10 which
allows upto a 10 second dts correction for 48 kHz audio streams while
accommodating 99.9% of uint32 range.
---
v2 changes:
mp4-negative-stts-problem.mp4 plays in sync with the default value
chosen.
stts adjustment shifted to mov_read_stts so that any downstream code
that references raw stts does not have to contend with possibly changed
stts values.
libavformat/isom.h | 1 +
libavformat/mov.c | 64 +++++++++++++++++++++++++++-------------------
2 files changed, 39 insertions(+), 26 deletions(-)
diff --git a/libavformat/isom.h b/libavformat/isom.h
index ef8f19b18c..625dea8421 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -305,6 +305,7 @@ typedef struct MOVContext {
int32_t movie_display_matrix[3][3]; ///< display matrix from mvhd
int have_read_mfra_size;
uint32_t mfra_size;
+ uint32_t max_stts_delta;
} MOVContext;
int ff_mp4_read_descr_len(AVIOContext *pb);
diff --git a/libavformat/mov.c b/libavformat/mov.c
index 2aed6e80ef..a36752c6a4 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -2925,6 +2925,9 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
unsigned int i, entries, alloc_size = 0;
int64_t duration = 0;
int64_t total_sample_count = 0;
+ int64_t current_dts = 0;
+ int64_t last_dts = 0;
+ int64_t dts_correction = 0;
if (c->fc->nb_streams < 1)
return 0;
@@ -2948,6 +2951,7 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
for (i = 0; i < entries && !pb->eof_reached; i++) {
unsigned int sample_duration;
unsigned int sample_count;
+ unsigned int stts_warn = 0;
unsigned int min_entries = FFMIN(FFMAX(i + 1, 1024 * 1024), entries);
MOVStts *stts_data = av_fast_realloc(sc->stts_data, &alloc_size,
min_entries * sizeof(*sc->stts_data));
@@ -2965,13 +2969,41 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
sc->stts_data[i].count= sample_count;
sc->stts_data[i].duration= sample_duration;
- av_log(c->fc, AV_LOG_TRACE, "sample_count=%d, sample_duration=%d\n",
+ av_log(c->fc, AV_LOG_TRACE, "sample_count=%u, sample_duration=%u\n",
sample_count, sample_duration);
- duration+=(int64_t)sample_duration*(uint64_t)sample_count;
- total_sample_count+=sample_count;
- }
+ for (int j = 0; j < sample_count; j++) {
+ /* STTS sample offsets are uint32 but some files store it as int32
+ * with negative values used to correct DTS delays.
+ There may be abnormally large values as well. */
+ if (sample_duration > c->max_stts_delta) {
+ // assume high delta is a negative correction if greater than c->max_stts_delta
+ int32_t delta_magnitude = *((int32_t *)&sample_duration);
+ av_log_once(c->fc, AV_LOG_WARNING, AV_LOG_DEBUG, &stts_warn,
+ "Too large sample offset %u in stts entry %u with count %u in st:%d. Clipping to 1.\n",
+ sample_duration, i, sample_count, st->index);
+ sc->stts_data[i].duration = 1;
+ dts_correction += (delta_magnitude < 0 ? delta_magnitude - 1 : 0);
+ }
+ current_dts += sc->stts_data[i].duration;
+
+ if (!dts_correction || current_dts + dts_correction > last_dts) {
+ current_dts += dts_correction;
+ if (!j)
+ sc->stts_data[i].duration += dts_correction/sample_count;
+ dts_correction = 0;
+ } else {
+ /* Avoid creating non-monotonous DTS */
+ dts_correction += current_dts - last_dts - 1;
+ current_dts = last_dts + 1;
+ }
+ last_dts = current_dts;
+ }
+ duration+=(int64_t)sc->stts_data[i].duration*(uint64_t)sc->stts_data[i].count;
+ total_sample_count+=sc->stts_data[i].count;
+
+ }
sc->stts_count = i;
if (duration > 0 &&
@@ -3856,13 +3888,10 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
unsigned int distance = 0;
unsigned int rap_group_index = 0;
unsigned int rap_group_sample = 0;
- int64_t last_dts = 0;
- int64_t dts_correction = 0;
int rap_group_present = sc->rap_group_count && sc->rap_group;
int key_off = (sc->keyframe_count && sc->keyframes[0] > 0) || (sc->stps_count && sc->stps_data[0] > 0);
current_dts -= sc->dts_shift;
- last_dts = current_dts;
if (!sc->sample_count || sti->nb_index_entries)
return;
@@ -3973,26 +4002,8 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
current_offset += sample_size;
stream_size += sample_size;
- /* A negative sample duration is invalid based on the spec,
- * but some samples need it to correct the DTS. */
- if (sc->stts_data[stts_index].duration < 0) {
- av_log(mov->fc, AV_LOG_WARNING,
- "Invalid SampleDelta %d in STTS, at %d st:%d\n",
- sc->stts_data[stts_index].duration, stts_index,
- st->index);
- dts_correction += sc->stts_data[stts_index].duration - 1;
- sc->stts_data[stts_index].duration = 1;
- }
current_dts += sc->stts_data[stts_index].duration;
- if (!dts_correction || current_dts + dts_correction > last_dts) {
- current_dts += dts_correction;
- dts_correction = 0;
- } else {
- /* Avoid creating non-monotonous DTS */
- dts_correction += current_dts - last_dts - 1;
- current_dts = last_dts + 1;
- }
- last_dts = current_dts;
+
distance++;
stts_sample++;
current_sample++;
@@ -8577,6 +8588,7 @@ static const AVOption mov_options[] = {
{ "decryption_key", "The media decryption key (hex)", OFFSET(decryption_key), AV_OPT_TYPE_BINARY, .flags = AV_OPT_FLAG_DECODING_PARAM },
{ "enable_drefs", "Enable external track support.", OFFSET(enable_drefs), AV_OPT_TYPE_BOOL,
{.i64 = 0}, 0, 1, FLAGS },
+ { "max_stts_delta", "treat offsets above this value as invalid", OFFSET(max_stts_delta), AV_OPT_TYPE_INT, {.i64 = UINT_MAX-48000*10 }, 0, UINT_MAX, .flags = AV_OPT_FLAG_DECODING_PARAM },
{ NULL },
};
--
2.33.0
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