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

[Andreas Rheinhardt]

On Tue, Dec 24, 2019 at 1:58 AM Andreas Rheinhardt <
andreas.rheinhardt at gmail.com> wrote:

> Andreas Rheinhardt:
> > Andreas Rheinhardt:
> >> 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
> >>>
> >> Another ping for the three unmerged patches of this patchset.
> >>
> >> - Andreas
> >>
> > Another ping for the two unmerged patches of this patchset; and also
> > for the other patch fixing uninitialized reads in the vobsub demuxer:
> > https://ffmpeg.org/pipermail/ffmpeg-devel/2019-October/251961.html
> >
> > - Andreas
> >
> Ping.
>
> - Andreas
>

Ping.

- Andreas