[FFmpeg-devel] [PATCH 2/4] avformat/mpeg: Remove secondary packet for reading VobSub

[Andreas Rheinhardt]

Andreas Rheinhardt:
> When vobsub_read_packet() reads a packet, it uses a dedicated AVPacket
> to get the subtitle timing and position from an FFDemuxSubtitlesQueue
> (which has been filled with this data during reading the idx file in
> vobsub_read_header); afterwards the actual subtitle data is read into
> the packet destined for output and the timing and position are copied
> to this packet. Afterwards, the local packet is unreferenced.
> 
> This can be simplified: Simply use the output packet to get the timing
> and position from the FFDemuxSubtitlesQueue. The packet's size will be
> zero afterwards, so that it can be directly used to read the actual
> subtitle data. This makes copying the packet fields as well as
> unreferencing the local packet unecessary and also removes an instance
> of usage of sizeof(AVPacket) in libavformat.
> 
> The only difference is that the returned packet will already be flagged
> as a keyframe. This currently only happens in compute_pkt_fields().
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavformat/mpeg.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/libavformat/mpeg.c b/libavformat/mpeg.c
> index bd182e4429..7daa72f7ce 100644
> --- a/libavformat/mpeg.c
> +++ b/libavformat/mpeg.c
> @@ -912,7 +912,6 @@ static int vobsub_read_packet(AVFormatContext *s, AVPacket *pkt)
>      FFDemuxSubtitlesQueue *q;
>      AVIOContext *pb = vobsub->sub_ctx->pb;
>      int ret, psize, total_read = 0, i;
> -    AVPacket idx_pkt = { 0 };
>  
>      int64_t min_ts = INT64_MAX;
>      int sid = 0;
> @@ -927,24 +926,22 @@ static int vobsub_read_packet(AVFormatContext *s, AVPacket *pkt)
>          }
>      }
>      q = &vobsub->q[sid];
> -    ret = ff_subtitles_queue_read_packet(q, &idx_pkt);
> +    /* The returned packet will have size zero,
> +     * so that it can be directly used with av_grow_packet. */
> +    ret = ff_subtitles_queue_read_packet(q, pkt);
>      if (ret < 0)
>          return ret;
>  
>      /* compute maximum packet size using the next packet position. This is
>       * useful when the len in the header is non-sense */
>      if (q->current_sub_idx < q->nb_subs) {
> -        psize = q->subs[q->current_sub_idx].pos - idx_pkt.pos;
> +        psize = q->subs[q->current_sub_idx].pos - pkt->pos;
>      } else {
>          int64_t fsize = avio_size(pb);
> -        psize = fsize < 0 ? 0xffff : fsize - idx_pkt.pos;
> +        psize = fsize < 0 ? 0xffff : fsize - pkt->pos;
>      }
>  
> -    avio_seek(pb, idx_pkt.pos, SEEK_SET);
> -
> -    av_init_packet(pkt);
> -    pkt->size = 0;
> -    pkt->data = NULL;
> +    avio_seek(pb, pkt->pos, SEEK_SET);
>  
>      do {
>          int n, to_read, startcode;
> @@ -968,7 +965,7 @@ static int vobsub_read_packet(AVFormatContext *s, AVPacket *pkt)
>          total_read += pkt_size;
>  
>          /* the current chunk doesn't match the stream index (unlikely) */
> -        if ((startcode & 0x1f) != s->streams[idx_pkt.stream_index]->id)
> +        if ((startcode & 0x1f) != s->streams[pkt->stream_index]->id)
>              break;
>  
>          ret = av_grow_packet(pkt, to_read);
> @@ -980,16 +977,10 @@ static int vobsub_read_packet(AVFormatContext *s, AVPacket *pkt)
>              pkt->size -= to_read - n;
>      } while (total_read < psize);
>  
> -    pkt->pts = pkt->dts = idx_pkt.pts;
> -    pkt->pos = idx_pkt.pos;
> -    pkt->stream_index = idx_pkt.stream_index;
> -
> -    av_packet_unref(&idx_pkt);
>      return 0;
>  
>  fail:
>      av_packet_unref(pkt);
> -    av_packet_unref(&idx_pkt);
>      return ret;
>  }
>  
> 
Ping.

- Andreas