[FFmpeg-devel] [PATCH] mpegts: limit teletext timestamps to [pcr; pcr + 40.6ms] range.

[Michael Niedermayer]

On Mon, Sep 24, 2012 at 08:51:28PM +0200, Reimar Döffinger wrote:
> The specification says they should not be buffered longer than
> that, and this is also necessary since e.g. ORF HD sends teletext
> with PES timestamps that are vastly off.
> 
> Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
> ---
>  libavformat/mpegts.c |   18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
> index c39cf45..b8fa332 100644
> --- a/libavformat/mpegts.c
> +++ b/libavformat/mpegts.c
> @@ -676,6 +676,16 @@ static void new_pes_packet(PESContext *pes, AVPacket *pkt)
>          pkt->stream_index = pes->st->index;
>      pkt->pts = pes->pts;
>      pkt->dts = pes->dts;
> +    if (pes->st->codec->codec_id == AV_CODEC_ID_DVB_TELETEXT) {
> +        // teletext packets do not always have correct timestamps,
> +        // the standard says they should be handled after 40.6 ms at most.
> +        int64_t pcr = pes->ts->cur_pcr / 300;
> +        if (pkt->dts == AV_NOPTS_VALUE || pkt->dts < pcr) {
> +            pkt->pts = pkt->dts = pcr;
> +        } else if (pes->dts > pcr + 3654) {
> +            pkt->pts = pkt->dts = pcr + 4654;
> +        }
> +    }
>      /* store position of first TS packet of this PES packet */
>      pkt->pos = pes->ts_packet_pos;
>      pkt->flags = pes->flags;
> @@ -1668,6 +1678,9 @@ static void sdt_cb(MpegTSFilter *filter, const uint8_t *section, int section_len
>      }
>  }
>  
> +static int parse_pcr(int64_t *ppcr_high, int *ppcr_low,
> +                     const uint8_t *packet);
> +
>  /* handle one TS packet */
>  static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
>  {
> @@ -1677,6 +1690,8 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
>          has_adaptation, has_payload;
>      const uint8_t *p, *p_end;
>      int64_t pos;
> +    int64_t pcr_h;
> +    int pcr_l;
>  
>      pid = AV_RB16(packet + 1) & 0x1fff;
>      if(pid && discard_pid(ts, pid))
> @@ -1733,6 +1748,9 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
>      pos = avio_tell(ts->stream->pb);
>      ts->pos47= pos % ts->raw_packet_size;
>  
> +    if (parse_pcr(&pcr_h, &pcr_l, packet) == 0)
> +        ts->cur_pcr = pcr_h * 300 + pcr_l;
> +

this doesnt look correct,
the way i remember the spec is that the pcr has to be taken from the
right stream (above looks like its taken from any stream) and then
extrapolated based on bitrate and amount of data
but the maximum time between PCRs of a program is 0.1 sec so if you
want to be sloppy simply taking the last of the right stream might
work with some greater tolerance on the timestamps

[...]
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