[FFmpeg-devel] [PATCH 2/3] avformat/fifo: add option to write packets in paced way

[Nicolas George]

leozhang (12020-04-29):
> Signed-off-by: leozhang <leozhang at qiyi.com>
> ---
>  doc/muxers.texi    |  3 +++
>  libavformat/fifo.c | 19 +++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index a74cbc4..5140c00 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -2274,6 +2274,9 @@ queue overflow or failure. This option is set to 0 (false) by default.
>  @item output_delay
>  Time to delay output, in microseconds. Default value is 0.
>  

> + at item paced
> +If set to 1 (true), write packets in paced way. Default value is 0 (false).

This does not explain to somebody who does not already know. Please have
a look at the doc for the filter "realtime" and use a similar wording,
preferably with cross-references.

> +
>  @end table
>  
>  @subsection Examples
> diff --git a/libavformat/fifo.c b/libavformat/fifo.c
> index bdecf2d..81b7e9e 100644
> --- a/libavformat/fifo.c
> +++ b/libavformat/fifo.c
> @@ -79,6 +79,12 @@ typedef struct FifoContext {
>  
>      /* Time to delay output, in microseconds */
>      uint64_t output_delay;
> +
> +    /* If set to 1, write packets in paced way */
> +    int paced;
> +
> +    /* Time to start */

> +    uint64_t start_time;

The return value of av_gettime_relative() is signed.

>  } FifoContext;
>  
>  typedef struct FifoThreadContext {
> @@ -184,6 +190,14 @@ static int fifo_thread_write_packet(FifoThreadContext *ctx, AVPacket *pkt)
>      src_tb = avf->streams[s_idx]->time_base;
>      dst_tb = avf2->streams[s_idx]->time_base;
>      av_packet_rescale_ts(pkt, src_tb, dst_tb);
> +    if (fifo->paced) {
> +        uint64_t pts = av_rescale_q(pkt->dts, dst_tb, AV_TIME_BASE_Q);
> +        uint64_t now = av_gettime_relative() - fifo->start_time;

> +        av_assert0(now >= fifo->output_delay);

av_gettime_relative() is not guaranteed to be monotonic, an assert is
not acceptable here.

> +        if (pts > now - fifo->output_delay) {

You probably need to make provisions for when the process was paused and
then resumed, and for timestamps discontinuities.

> +            av_usleep(pts - (now - fifo->output_delay));

The argument to av_usleep() is unsigned, you are passing uint64_t, it
can overflow.

> +        }

> +    }
>  
>      ret = av_write_frame(avf2, pkt);
>      if (ret >= 0)
> @@ -515,6 +529,8 @@ static int fifo_init(AVFormatContext *avf)
>          return AVERROR(ret);
>      fifo->overflow_flag_lock_initialized = 1;
>  
> +    fifo->start_time = av_gettime_relative();
> +
>      return 0;
>  }
>  
> @@ -637,6 +653,9 @@ static const AVOption options[] = {
>          {"output_delay", "Time to delay output, in microseconds", OFFSET(output_delay),
>           AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM},
>  
> +        {"paced", "Write packets in paced way", OFFSET(paced),
> +         AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, AV_OPT_FLAG_ENCODING_PARAM},
> +
>          {NULL},
>  };
>  

Regards,

-- 
  Nicolas George
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