[FFmpeg-devel] [PATCH] avformat/mov: support sidx reference_type = 1

[James Almer]

On 7/30/2024 11:56 AM, jiangjie wrote:
> ---
>   libavformat/mov.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 1052691936..38f015a766 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -5964,11 +5964,10 @@ static int mov_read_sidx(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>           int index;
>           MOVFragmentStreamInfo * frag_stream_info;
>           uint32_t size = avio_rb32(pb);
> +        // ReferenceType = (size & (1 << 31)) ? 1 : 0
> +        size = size & 0x7FFFFFFF;
> +
>           uint32_t duration = avio_rb32(pb);
> -        if (size & 0x80000000) {
> -            avpriv_request_sample(c->fc, "sidx reference_type 1");
> -            return AVERROR_PATCHWELCOME;
> -        }

Per the spec:

"Each entry in the SegmentIndexBox contains a reference type that 
indicates whether the reference points directly to the media bytes of a 
referenced leaf subsegment, or to a SegmentIndexBox that describes how 
the referenced subsegment is further subdivided; as a result, the 
segment may be indexed in a ‘hierarchical’ or ‘daisy-chain’ or other 
form by documenting time and byte offset information for other 
SegmentIndexBoxes applying to portions of the same (sub)segment"

And

"reference_type set to 1 indicates that the reference is to a 
SegmentIndexBox; otherwise the reference is to media content (e.g., in 
the case of files based on this document, to a MovieFragmentBox); if a 
separate index segment is used, then entries with reference type 1 are 
in the index segment, and entries with reference type 0 are in the media 
file".

All the code below this part assumes movie fragment, not another sidx 
box, so this patch is just ignoring the reference_type bit and thus is 
not correct.
Proper support for reference_type == 1 is needed.

>           avio_rb32(pb); // sap_flags
>           timestamp = av_rescale_q(pts, timescale, st->time_base);
>