[FFmpeg-devel] [PATCH] avformat/mov: Fix decoding fragmented MP4 with multiple sample entries and empty stsc

[Dimitry Andric]

When decoding fragmented MP4 files that have an empty stsc box, and
instead contain sample description indexes in their tfhd boxes, the mov
demuxer does not notify the decoder whenever the current sample
description index changes. If the SPS or PPS changed sufficiently, this
can lead to unexpected decoding errors.

To fix this, in mov_finalize_packet(), when stsc_data is not available,
use get_frag_stream_info_from_pkt() to get at the current fragment
stream info, and retrieve the current sample description index from
there. Then use that index in a similar manner as the stsc case.

Signed-off-by: Dimitry Andric <dimitry at unified-streaming.com>
---
 libavformat/mov.c | 50 ++++++++++++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 20 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 452690090c..ead89192f4 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -10756,25 +10756,29 @@ static int mov_switch_root(AVFormatContext *s, int64_t target, int index)
     return 1;
 }
 
-static int mov_change_extradata(AVStream *st, AVPacket *pkt)
+static int mov_change_extradata(AVStream *st, AVPacket *pkt, int stsd_id)
 {
     MOVStreamContext *sc = st->priv_data;
     uint8_t *side, *extradata;
     int extradata_size;
 
-    /* Save the current index. */
-    sc->last_stsd_index = sc->stsc_data[sc->stsc_index].id - 1;
+    if (stsd_id > 0 &&
+        stsd_id - 1 < sc->stsd_count &&
+        stsd_id - 1 != sc->last_stsd_index) {
+        /* Save the current index. */
+        sc->last_stsd_index = stsd_id - 1;
 
-    /* Notify the decoder that extradata changed. */
-    extradata_size = sc->extradata_size[sc->last_stsd_index];
-    extradata = sc->extradata[sc->last_stsd_index];
-    if (st->discard != AVDISCARD_ALL && extradata_size > 0 && extradata) {
-        side = av_packet_new_side_data(pkt,
-                                       AV_PKT_DATA_NEW_EXTRADATA,
-                                       extradata_size);
-        if (!side)
-            return AVERROR(ENOMEM);
-        memcpy(side, extradata, extradata_size);
+        /* Notify the decoder that extradata changed. */
+        extradata_size = sc->extradata_size[sc->last_stsd_index];
+        extradata = sc->extradata[sc->last_stsd_index];
+        if (st->discard != AVDISCARD_ALL && extradata_size > 0 && extradata) {
+            side = av_packet_new_side_data(pkt,
+                                           AV_PKT_DATA_NEW_EXTRADATA,
+                                           extradata_size);
+            if (!side)
+                return AVERROR(ENOMEM);
+            memcpy(side, extradata, extradata_size);
+        }
     }
 
     return 0;
@@ -10893,13 +10897,10 @@ static int mov_finalize_packet(AVFormatContext *s, AVStream *st, AVIndexEntry *s
 
     /* Multiple stsd handling. */
     if (sc->stsc_data) {
-        if (sc->stsc_data[sc->stsc_index].id > 0 &&
-            sc->stsc_data[sc->stsc_index].id - 1 < sc->stsd_count &&
-            sc->stsc_data[sc->stsc_index].id - 1 != sc->last_stsd_index) {
-            int ret = mov_change_extradata(st, pkt);
-            if (ret < 0)
-                return ret;
-        }
+        int stsd_id = sc->stsc_data[sc->stsc_index].id;
+        int ret = mov_change_extradata(st, pkt, stsd_id);
+        if (ret < 0)
+            return ret;
 
         /* Update the stsc index for the next sample */
         sc->stsc_sample++;
@@ -10908,6 +10909,15 @@ static int mov_finalize_packet(AVFormatContext *s, AVStream *st, AVIndexEntry *s
             sc->stsc_index++;
             sc->stsc_sample = 0;
         }
+    } else {
+        MOVContext *mov = s->priv_data;
+        MOVFragmentStreamInfo *frag_stream_info = get_frag_stream_info_from_pkt(&mov->frag_index, pkt, sc->id);
+        if (frag_stream_info) {
+            int stsd_id = frag_stream_info->stsd_id;
+            int ret = mov_change_extradata(st, pkt, stsd_id);
+            if (ret < 0)
+                return ret;
+        }
     }
 
     return 0;
-- 
2.43.0