avformat/mov: fix missing extra data updating

The stsc_index is checked and updated for the next sample. If the
next sample needs to update stsd_index and stsc_index, then only
stsc_index is updated, which leads to a missing
AV_PKT_DATA_NEW_EXTRADATA. For example, the sample in the second
chunk needs to update both.

entry[0]
    first_chunk = 1
    samples_per_chunk = 3
    sample_description_index = 1
entry[1]
    first_chunk = 2
    samples_per_chunk = 1
    sample_description_index = 2
entry[2]
    first_chunk = 3
    samples_per_chunk = 8
    sample_description_index = 2

The fix is simple: first check and update stsd_index for current
sample, then check and update stsc_index for the next.
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

libavformat/mov.c

@@ -8745,20 +8745,20 @@ static int mov_read_packet(AVFormatContext *s, AVPacket *pkt)
 
     /* Multiple stsd handling. */
     if (sc->stsc_data) {
-        /* Keep track of the stsc index for the given sample, then check
-        * if the stsd index is different from the last used one. */
+        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) {
+            ret = mov_change_extradata(sc, pkt);
+            if (ret < 0)
+                return ret;
+        }
+
+        /* Update the stsc index for the next sample */
         sc->stsc_sample++;
         if (mov_stsc_index_valid(sc->stsc_index, sc->stsc_count) &&
             mov_get_stsc_samples(sc, sc->stsc_index) == sc->stsc_sample) {
             sc->stsc_index++;
             sc->stsc_sample = 0;
-        /* Do not check indexes after a switch. */
-        } else 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) {
-            ret = mov_change_extradata(sc, pkt);
-            if (ret < 0)
-                return ret;
         }
     }