[FFmpeg-devel] [PATCH v2] avformat/mov: adjust 0 values in stts

[Gyan Doshi <ffmpeg@gyani.pro>]

As per ISO 14496-12, sample duration of 0 is invalid except for
the last entry. However, some files may use it to stall dts
progress in order to recover from a desync.

In addition, catch and fix 0 value for sample count.
---
v2:

adjust dts if 0 duration is encountered

 libavformat/mov.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 351ecde770..7e90e24bd5 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -2970,16 +2970,22 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         av_log(c->fc, AV_LOG_TRACE, "sample_count=%u, sample_duration=%u\n",
                 sample_count, sample_duration);
 
+        if (!sample_count) {
+        av_log(c->fc, AV_LOG_WARNING, "invalid sample count of 0 in stts for st %d at entry %u; changing to 1.\n",
+               c->fc->nb_streams-1, i);
+        sc->stts_data[i].count = sample_count = 1;
+        }
+
         /* 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) {
+        if (sample_duration > c->max_stts_delta || !sample_duration) {
             // assume high delta is a correction if negative when cast as int32
             int32_t delta_magnitude = (int32_t)sample_duration;
-            av_log(c->fc, AV_LOG_WARNING, "Too large sample offset %u in stts entry %u with count %u in st:%d. Clipping to 1.\n",
+            av_log(c->fc, AV_LOG_WARNING, "Too large or zero sample offset %u in stts entry %u with count %u in st:%d. Setting to 1.\n",
                    sample_duration, i, sample_count, st->index);
             sc->stts_data[i].duration = 1;
-            corrected_dts += (delta_magnitude < 0 ? (int64_t)delta_magnitude : 1) * sample_count;
+            corrected_dts += (delta_magnitude <= 0 ? (int64_t)delta_magnitude : 1) * sample_count;
         } else {
             corrected_dts += sample_duration * sample_count;
         }
@@ -2987,7 +2993,7 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         current_dts += sc->stts_data[i].duration * sample_count;
 
         if (current_dts > corrected_dts) {
-            int64_t drift = (current_dts - corrected_dts)/FFMAX(sample_count, 1);
+            int64_t drift = (current_dts - corrected_dts)/sample_count;
             uint32_t correction = (sc->stts_data[i].duration > drift) ? drift : sc->stts_data[i].duration - 1;
             current_dts -= correction * sample_count;
             sc->stts_data[i].duration -= correction;
-- 
2.33.0

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