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. Negative values of under 1 second are used to adjust
dts.
Unit is the track time scale. Default is INT_MAX which maintains current
handling.
---
doc/demuxers.texi | 5 +++++
libavformat/isom.h | 1 +
libavformat/mov.c | 14 +++++++++-----
3 files changed, 15 insertions(+), 5 deletions(-)
diff --git a/doc/demuxers.texi b/doc/demuxers.texi
index cab8a7072c..f91ac92cf1 100644
--- a/doc/demuxers.texi
+++ b/doc/demuxers.texi
@@ -715,6 +715,11 @@ specify.
16-byte key, in hex, to decrypt files encrypted using ISO Common Encryption
(CENC/AES-128 CTR; ISO/IEC 23001-7).
@end table
+@item max_stts_delta
+The sample offsets stored in a track's stts box are 32-bit unsigned integers.
However, very large values usually indicate
+a value written by error or a storage of a small negative value as a way to
correct accumulated DTS delay.
+Range is 0 to UINT_MAX. Default is INT_MAX.
+
@subsection Audible AAX
Audible AAX files are encrypted M4B files, and they can be decrypted by
specifying a 4 byte activation secret.
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 451cb78bbf..bbda07ac42 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -3965,14 +3965,17 @@ 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) {
+ /* 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 (sc->stts_data[stts_index].duration > mov->max_stts_delta) {
+ // assume high delta is a negative correction if less than
1 second
+ int32_t delta_magnitude = *((int32_t
*)&sc->stts_data[stts_index].duration);
av_log(mov->fc, AV_LOG_WARNING,
- "Invalid SampleDelta %d in STTS, at %d st:%d\n",
+ "Correcting too large SampleDelta %u 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;
+ dts_correction += (delta_magnitude < 0 &&
FFABS(delta_magnitude) < sc->time_scale ? delta_magnitude - 1 : 0);
sc->stts_data[stts_index].duration = 1;
}
current_dts += sc->stts_data[stts_index].duration;
@@ -8566,6 +8569,7 @@ 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 = INT_MAX}, 0, UINT_MAX, .flags
= AV_OPT_FLAG_DECODING_PARAM },
{ NULL },
};
--
2.33.0
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