[FFmpeg-devel] [PATCH] avformat/movenc: use stream indexes when generating track ids

[FFmpeg-devel] [PATCH] avformat/movenc: use stream indexes when generating track ids

[James Almer]

In some scenarios nb_tracks isn't the same as nb_streams, so a given id may end
up being used for two separate streams.

e.g. when muxing an IAMF track followed by a video track, if the IAMF track
consists of several streams, the video track would end up having an id of 2,
which may also be used by one of the IAMF streams.

Signed-off-by: James Almer <jamrial@gmail.com>
---
 libavformat/movenc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 8e4a037e46..8d91059081 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -4944,11 +4944,15 @@ static int mov_setup_track_ids(MOVMuxContext *mov, AVFormatContext *s)
             mov->tracks[i].track_id = i >= mov->nb_streams ? ++next_generated_track_id : mov->tracks[i].st->id;
         }
     } else {
+        int last_track_id = 0;
         for (i = 0; i < mov->nb_tracks; i++) {
             if (mov->tracks[i].entry <= 0 && !(mov->flags & FF_MOV_FLAG_FRAGMENT))
                 continue;
 
-            mov->tracks[i].track_id = i + 1;
+            last_track_id =
+            mov->tracks[i].track_id = (mov->tracks[i].st
+                                       ? FFMAX(mov->tracks[i].st->index, last_track_id)
+                                       : FFMAX((i ? mov->tracks[i - 1].track_id : i), last_track_id)) + 1;
         }
     }
 
-- 
2.46.0

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Re: [FFmpeg-devel] [PATCH] avformat/movenc: use stream indexes when generating track ids

[Marton Balint]

On Sat, 3 Aug 2024, James Almer wrote:

> In some scenarios nb_tracks isn't the same as nb_streams, so a given id may end
> up being used for two separate streams.
>
> e.g. when muxing an IAMF track followed by a video track, if the IAMF track
> consists of several streams, the video track would end up having an id of 2,
> which may also be used by one of the IAMF streams.
>
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
> libavformat/movenc.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index 8e4a037e46..8d91059081 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -4944,11 +4944,15 @@ static int mov_setup_track_ids(MOVMuxContext *mov, AVFormatContext *s)
>             mov->tracks[i].track_id = i >= mov->nb_streams ? ++next_generated_track_id : mov->tracks[i].st->id;
>         }
>     } else {
> +        int last_track_id = 0;
>         for (i = 0; i < mov->nb_tracks; i++) {
>             if (mov->tracks[i].entry <= 0 && !(mov->flags & FF_MOV_FLAG_FRAGMENT))
>                 continue;
>
> -            mov->tracks[i].track_id = i + 1;
> +            last_track_id =
> +            mov->tracks[i].track_id = (mov->tracks[i].st
> +                                       ? FFMAX(mov->tracks[i].st->index, last_track_id)
> +                                       : FFMAX((i ? mov->tracks[i - 1].track_id : i), last_track_id)) + 1;

Are you sure mov->tracks[i-1].track_id is always initialized? Because 
there is a condition above which can skip certain tracks. Maybe it would 
be safer to use last_track_id instead of mov->tracks[i-1].track_id ?

Thanks,
Marton
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