[FFmpeg-devel] [PATCH] avformat/mov: fix missing extra data updating

[FFmpeg-devel] [PATCH] avformat/mov: fix missing extra data updating

[Zhao Zhili]

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.
---
 libavformat/mov.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 6c847de164..c9d4f2ef43 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -8591,20 +8591,20 @@ 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;
         }
     }
 
-- 
2.31.1

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Re: [FFmpeg-devel] [PATCH] avformat/mov: fix missing extra data updating

["zhilizhao(赵志立)"]

> On Mar 30, 2022, at 2:04 AM, Zhao Zhili <quinkblack@foxmail.com> wrote:
> 
> 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.
> ---
> libavformat/mov.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 6c847de164..c9d4f2ef43 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -8591,20 +8591,20 @@ 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;
>         }
>     }
> 


Multi sample entry is a less used feature. Since we have it, better keep it
work. This patch fixed a corner case.

Will apply this week unless there are objections.
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