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

[Andreas Rheinhardt]

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