[FFmpeg-devel] [PATCH v3] avformat/mpegts: reduce buffering during initialization

[Michael Niedermayer]

On Wed, Mar 06, 2019 at 10:15:36PM -0500, Andriy Gelman wrote:
> From: Andriy Gelman <andriy.gelman at gmail.com>
> 
> Reduces buffering latency with low bitrate streams, where
> 8192 bytes can mean several seconds.
> ---
>  libavformat/mpegts.c | 60 +++++++++++++++++++++++++++-----------------
>  1 file changed, 37 insertions(+), 23 deletions(-)
> 
> diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
> index b04fd7b4f4..7d03500043 100644
> --- a/libavformat/mpegts.c
> +++ b/libavformat/mpegts.c
> @@ -53,6 +53,10 @@
>          (prev_dividend) = (dividend);                                          \
>      } while (0)
>  
> +#define PROBE_PACKET_MAX_BUF 8192
> +#define PROBE_PACKET_STEP 512
> +#define PROBE_PACKET_MARGIN 5
> +
>  enum MpegTSFilterType {
>      MPEGTS_PES,
>      MPEGTS_SECTION,
> @@ -591,28 +595,42 @@ static int analyze(const uint8_t *buf, int size, int packet_size,
>      return best_score - FFMAX(stat_all - 10*best_score, 0)/10;
>  }
>  
> -/* autodetect fec presence. Must have at least 1024 bytes  */
> -static int get_packet_size(const uint8_t *buf, int size)
> +/* autodetect fec presence */
> +static int get_packet_size(AVIOContext* pb)
>  {
>      int score, fec_score, dvhs_score;
> +    int margin;
> +    int ret;
>  
> -    if (size < (TS_FEC_PACKET_SIZE * 5 + 1))
> -        return AVERROR_INVALIDDATA;
> +    /*init buffer to store stream for probing */
> +    uint8_t buf[PROBE_PACKET_MAX_BUF] = {0};
> +    int buf_size = 0;
>  
> -    score      = analyze(buf, size, TS_PACKET_SIZE,      0);
> -    dvhs_score = analyze(buf, size, TS_DVHS_PACKET_SIZE, 0);
> -    fec_score  = analyze(buf, size, TS_FEC_PACKET_SIZE,  0);
> -    av_log(NULL, AV_LOG_TRACE, "score: %d, dvhs_score: %d, fec_score: %d \n",
> -            score, dvhs_score, fec_score);
> -
> -    if (score > fec_score && score > dvhs_score)
> -        return TS_PACKET_SIZE;
> -    else if (dvhs_score > score && dvhs_score > fec_score)
> -        return TS_DVHS_PACKET_SIZE;
> -    else if (score < fec_score && dvhs_score < fec_score)
> -        return TS_FEC_PACKET_SIZE;
> -    else
> -        return AVERROR_INVALIDDATA;
> +    while (buf_size + PROBE_PACKET_STEP <= PROBE_PACKET_MAX_BUF) {
> +        ret = avio_read(pb, buf + buf_size, PROBE_PACKET_STEP);

have you tried avio_read_partial() ?
it may be better to request the full remaining size of the buffer and accept
whatever is available.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator
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