[FFmpeg-devel] [PATCH 1/2] libavformat: Support multiple thumbnails in HEIF

[James Almer]

On 7/16/2025 11:30 PM, Eric Joyner wrote:
> Prevents ffmpeg/ffprobe from erroring out when reading an HEIF that
> contains multiple hvcC thumbnails (e.g. from a Nikon Z6III camera).
> 
> Before, move_read_iref_thmb() would always override the stored
> thmb_item_id in the MOVContext with each new read thumbnail, causing a
> stream and item_id mismatch later in mov_parse_heif_items(), resulting
> in the "HEIF thumbnail doesn't reference a stream" error message.
> 
> To solve this,
> 
> - Turn thmb_item_id into an array of IDs because multiple thumbnails can
>    exist
> - Change check in mov_parse_heif_items() to compare against all stored
>    thumbnail IDs to see if any item missing a stream is in the list of
>    thumbnail IDs.
> 
> Signed-off-by: Eric Joyner <erj at erj.cc>
> ---
>   libavformat/isom.h |  3 ++-
>   libavformat/mov.c  | 24 +++++++++++++++++-------
>   2 files changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/libavformat/isom.h b/libavformat/isom.h
> index 10f882806e..94c9c65989 100644
> --- a/libavformat/isom.h
> +++ b/libavformat/isom.h
> @@ -376,7 +376,8 @@ typedef struct MOVContext {
>       int nb_heif_item;
>       HEIFGrid *heif_grid;
>       int nb_heif_grid;
> -    int thmb_item_id;
> +    int* thmb_item_id;
> +    int nb_thmb_item;
>       int64_t idat_offset;
>       int interleaved_read;
>   } MOVContext;
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index c935bbf0bf..7010e13b50 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -8972,6 +8972,7 @@ static int mov_read_iref_dimg(MOVContext *c, AVIOContext *pb, int version)
>   
>   static int mov_read_iref_thmb(MOVContext *c, AVIOContext *pb, int version)
>   {
> +    int *thmb_item_id;
>       int entries;
>       int to_item_id, from_item_id = version ? avio_rb32(pb) : avio_rb16(pb);
>   
> @@ -8986,10 +8987,15 @@ static int mov_read_iref_thmb(MOVContext *c, AVIOContext *pb, int version)
>       if (to_item_id != c->primary_item_id)
>           return 0;
>   
> -    c->thmb_item_id = from_item_id;
> +    /* Put thumnbail IDs into an array */
> +    thmb_item_id = av_dynarray2_add((void **)&c->thmb_item_id, &c->nb_thmb_item,
> +                                    sizeof(*c->thmb_item_id),
> +                                    (const void *)&from_item_id);
> +    if (!thmb_item_id)
> +        return AVERROR(ENOMEM);
>   
> -    av_log(c->fc, AV_LOG_TRACE, "thmb: from_item_id %d, entries %d\n",
> -           from_item_id, entries);
> +    av_log(c->fc, AV_LOG_TRACE, "thmb: from_item_id %d, entries %d, nb_thmb: %d\n",
> +           from_item_id, entries, c->nb_thmb_item);
>   
>       return 0;
>   }
> @@ -9859,6 +9865,7 @@ static int mov_read_close(AVFormatContext *s)
>           av_freep(&mov->heif_grid[i].tile_item_list);
>       }
>       av_freep(&mov->heif_grid);
> +    av_freep(&mov->thmb_item_id);
>   
>       return 0;
>   }
> @@ -10323,9 +10330,12 @@ static int mov_parse_heif_items(AVFormatContext *s)
>           if (!item)
>               continue;
>           if (!item->st) {
> -            if (item->item_id == mov->thmb_item_id) {
> -                av_log(s, AV_LOG_ERROR, "HEIF thumbnail doesn't reference a stream\n");
> -                return AVERROR_INVALIDDATA;
> +            for (int i = 0; i < mov->nb_thmb_item; i++) {

Changed the index variable to j to not shadow i, and pushed.

Thanks.

> +                if (item->item_id == mov->thmb_item_id[i]) {
> +                    av_log(s, AV_LOG_ERROR, "HEIF thumbnail ID %d doesn't reference a stream\n",
> +                           item->item_id);
> +                    return AVERROR_INVALIDDATA;
> +                }
>               }
>               continue;
>           }
> @@ -10476,7 +10486,7 @@ static int mov_read_header(AVFormatContext *s)
>   
>       mov->fc = s;
>       mov->trak_index = -1;
> -    mov->thmb_item_id = -1;
> +    mov->thmb_item_id = NULL;
>       mov->primary_item_id = -1;
>       mov->cur_item_id = -1;
>       /* .mov and .mp4 aren't streamable anyway (only progressive download if moov is before mdat) */

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