[FFmpeg-devel] [PATCH] avformat/mpegts: Check the next sync byte to avoid incorrectt detected raw packet size

[mypopy at gmail.com]

On Fri, May 15, 2020 at 6:23 PM <lance.lmwang at gmail.com> wrote:
>
> From: Limin Wang <lance.lmwang at gmail.com>
>
> reanalyze() may misdetect the new packet size as 204, but it's 188 still actualy,
> it'll cause many cc errors report and cannot be recovered. So it's better to check
> the next sync byte before skip the extra unused bytes.
>
> Also, it is best to change SIZE_STAT_THRESHOLD from 10 to 100? If the input stream has
> a master/slave switch serveral times, the raw size can be easily detected by mistake.
>
> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> ---
>  libavformat/mpegts.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
> index 0833d62..049555c 100644
> --- a/libavformat/mpegts.c
> +++ b/libavformat/mpegts.c
> @@ -2932,11 +2932,12 @@ static int read_packet(AVFormatContext *s, uint8_t *buf, int raw_packet_size,
>      return 0;
>  }
>
> -static void finished_reading_packet(AVFormatContext *s, int raw_packet_size)
> +static void finished_reading_packet(AVFormatContext *s, const uint8_t *data, int raw_packet_size)
>  {
>      AVIOContext *pb = s->pb;
>      int skip = raw_packet_size - TS_PACKET_SIZE;
> -    if (skip > 0)
> +    /* Check the next sync byte to avoid incorrectt detected raw packet size */
> +    if (skip > 0 && data[TS_PACKET_SIZE] != 0x47)
>          avio_skip(pb, skip);
>  }
>
> @@ -2985,7 +2986,7 @@ static int handle_packets(MpegTSContext *ts, int64_t nb_packets)
>          if (ret != 0)
>              break;
>          ret = handle_packet(ts, data, avio_tell(s->pb));
> -        finished_reading_packet(s, ts->raw_packet_size);
> +        finished_reading_packet(s, data, ts->raw_packet_size);
>          if (ret != 0)
>              break;
>      }
> @@ -3137,7 +3138,7 @@ static int mpegts_read_header(AVFormatContext *s)
>              pid = AV_RB16(data + 1) & 0x1fff;
>              if ((pcr_pid == -1 || pcr_pid == pid) &&
>                  parse_pcr(&pcr_h, &pcr_l, data) == 0) {
> -                finished_reading_packet(s, ts->raw_packet_size);
> +                finished_reading_packet(s, data, ts->raw_packet_size);
>                  pcr_pid = pid;
>                  packet_count[nb_pcrs] = nb_packets;
>                  pcrs[nb_pcrs] = pcr_h * 300 + pcr_l;
> @@ -3154,7 +3155,7 @@ static int mpegts_read_header(AVFormatContext *s)
>                      }
>                  }
>              } else {
> -                finished_reading_packet(s, ts->raw_packet_size);
> +                finished_reading_packet(s, data, ts->raw_packet_size);
>              }
>              nb_packets++;
>          }
> @@ -3194,7 +3195,7 @@ static int mpegts_raw_read_packet(AVFormatContext *s, AVPacket *pkt)
>      }
>      if (data != pkt->data)
>          memcpy(pkt->data, data, ts->raw_packet_size);
> -    finished_reading_packet(s, ts->raw_packet_size);
> +    finished_reading_packet(s, data, ts->raw_packet_size);
>      if (ts->mpeg2ts_compute_pcr) {
>          /* compute exact PCR for each packet */
>          if (parse_pcr(&pcr_h, &pcr_l, pkt->data) == 0) {
> --
> 1.8.3.1
>
Do you have a case to reproduce the cc errors report?