[FFmpeg-devel] [PATCH 04/12] avformat/mxfdec: compute both essence_offset and essence_length in mxf_compute_essence_containers

[Tomas Härdin]

sön 2018-06-10 klockan 12:36 +0200 skrev Marton Balint:
> Also compute the correct essence_offset and essence_length for all clip wrapped
> essences.
> 
> > Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  libavformat/mxfdec.c | 108 +++++++++++++++++++++++++++------------------------
>  1 file changed, 57 insertions(+), 51 deletions(-)
> 
> diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> index 1ab34f4873..67b0028e88 100644
> --- a/libavformat/mxfdec.c
> +++ b/libavformat/mxfdec.c
> @@ -98,6 +98,7 @@ typedef struct MXFPartition {
>      int pack_length;
>      int64_t pack_ofs;               ///< absolute offset of pack in file, including run-in
>      int64_t body_offset;
> +    KLVPacket first_essence_klv;
>  } MXFPartition;
>  
>  typedef struct MXFCryptoContext {
> @@ -2782,47 +2783,76 @@ static int mxf_parse_handle_partition_or_eof(MXFContext *mxf)
>      return mxf->parsing_backward ? mxf_seek_to_previous_partition(mxf) : 1;
>  }
>  
> +static int64_t round_to_kag(int64_t position, int kag_size)
> +{
> +    /* TODO: account for run-in? the spec isn't clear whether KAG should account for it */
> +    /* NOTE: kag_size may be any integer between 1 - 2^10 */
> +    int64_t ret = (position / kag_size) * kag_size;
> +    return ret == position ? ret : ret + kag_size;

This should probably just be

 return ((position + kag_size - 1) / kag_size) * kag_size;

but maybe there's some fine point I'm overlooking. What happens if
kag_size is a smallish value like 16?

A check for position > INT64_MAX - kag_size might also be appropriate.

> +}
> +
> +static MXFWrappingScheme mxf_get_wrapping_by_body_sid(AVFormatContext *s, int body_sid)
> +{
> +    for (int i = 0; i < s->nb_streams; i++) {
> +        MXFTrack *track = s->streams[i]->priv_data;
> +        if (track && track->body_sid == body_sid && track->wrapping != UnknownWrapped)
> +            return track->wrapping;
> +    }
> +    return UnknownWrapped;
> +}
> +
>  /**
>   * Figures out the proper offset and length of the essence container in each partition
>   */
> -static void mxf_compute_essence_containers(MXFContext *mxf)
> +static void mxf_compute_essence_containers(AVFormatContext *s)
>  {
> +    MXFContext *mxf = s->priv_data;
>      int x;
>  
> -    /* everything is already correct */
> -    if (mxf->op == OPAtom)
> -        return;
> -
>      for (x = 0; x < mxf->partitions_count; x++) {
>          MXFPartition *p = &mxf->partitions[x];
> +        MXFWrappingScheme wrapping;
>  
>          if (!p->body_sid)
>              continue;       /* BodySID == 0 -> no essence */
>  
> -        if (x >= mxf->partitions_count - 1)
> -            break;          /* FooterPartition - can't compute length (and we don't need to) */
> +        /* for non clip-wrapped essences we compute essence_offset
> +         * for clip wrapped essences we point essence_offset after the KL (usually klv.offset + 20 or 25)
> +         */
>  
> -        /* essence container spans to the next partition */
> -        p->essence_length = mxf->partitions[x+1].this_partition - p->essence_offset;
> +        wrapping = (mxf->op == OPAtom) ? ClipWrapped : mxf_get_wrapping_by_body_sid(s, p->body_sid);
>  
> -        if (p->essence_length < 0) {
> -            /* next ThisPartition < essence_offset */
> -            p->essence_length = 0;
> -            av_log(mxf->fc, AV_LOG_ERROR,
> -                   "partition %i: bad ThisPartition = %"PRIX64"\n",
> -                   x+1, mxf->partitions[x+1].this_partition);
> +        if (wrapping == ClipWrapped) {
> +            p->essence_offset = p->first_essence_klv.next_klv - p->first_essence_klv.length;
> +            p->essence_length = p->first_essence_klv.length;

Much nicer

> +        } else {
> +            int64_t op1a_essence_offset =
> +                p->this_partition +
> +                round_to_kag(p->pack_length,       p->kag_size) +
> +                round_to_kag(p->header_byte_count, p->kag_size) +
> +                round_to_kag(p->index_byte_count,  p->kag_size);

Is this really always the case? I guess with OP1a it isn't a huge
concern since the demuxer will find the next essence packet anyway. But
still..

I'm also fairly sure this is my code originally so.. :)

The rest looks OK

/Tomas