[FFmpeg-devel] fftools/ffmpeg: Added ability to set a input burst time before readrate is enforced

Implemented is the -irb <seconds> flag (i.e. "initial read burst") that
causes ffmpeg to read the specified number of seconds of input before a
given readrate starts to be enforced.  All inputs have to reach this
point before the readrate is enforced.  The reason for this change is,
in the scenario of live-streaming by transcoding from an pre-recorded or
delayed source to an HLS or DASH webroot, we can more quickly prime the
system of the first few seconds before the real-world read rate is
imposed.  Else, one must wait for an entire segment length before the
data can be fetched from the web server.

Signed-off-by: Davy Durham <ddurham@users.sourceforge.net>
---
  doc/ffmpeg.texi      |  2 ++
  fftools/ffmpeg.c     |  3 ++-
  fftools/ffmpeg.h     |  2 ++
  fftools/ffmpeg_opt.c | 13 +++++++++++++
  4 files changed, 19 insertions(+), 1 deletion(-)

      if (!f->pkt)
          exit_program(1);
@@ -3734,6 +3744,9 @@ const OptionDef options[] = {
      { "readrate",       HAS_ARG | OPT_FLOAT | OPT_OFFSET |
                          OPT_EXPERT | OPT_INPUT,                      { 
.off = OFFSET(readrate) },
          "read input at specified rate", "speed" },
+    { "irb",            HAS_ARG | OPT_DOUBLE | OPT_OFFSET |
+                        OPT_EXPERT | OPT_INPUT,                      { 
.off = OFFSET(initial_read_burst) },
+        "The initial amount of input to burst read before imposing any 
readrate", "seconds" },
      { "target",         HAS_ARG | OPT_PERFILE | OPT_OUTPUT,          { 
.func_arg = opt_target },
          "specify target file type (\"vcd\", \"svcd\", \"dvd\", \"dv\" 
or \"dv50\" "
          "with optional prefixes \"pal-\", \"ntsc-\" or \"film-\")", 
"type" },

Any update on this submission?  I never heard anything back, and I don't 
see it included in any branch. Or, is it that I just don't know where to 
look for the status of patches?

Thanks

On 2/23/23 02:05, Davy Durham wrote:
> Implemented is the -irb <seconds> flag (i.e. "initial read burst") that
> causes ffmpeg to read the specified number of seconds of input before a
> given readrate starts to be enforced.  All inputs have to reach this
> point before the readrate is enforced.  The reason for this change is,
> in the scenario of live-streaming by transcoding from an pre-recorded or
> delayed source to an HLS or DASH webroot, we can more quickly prime the
> system of the first few seconds before the real-world read rate is
> imposed.  Else, one must wait for an entire segment length before the
> data can be fetched from the web server.
>
> Signed-off-by: Davy Durham <ddurham@users.sourceforge.net>
> ---
>  doc/ffmpeg.texi      |  2 ++
>  fftools/ffmpeg.c     |  3 ++-
>  fftools/ffmpeg.h     |  2 ++
>  fftools/ffmpeg_opt.c | 13 +++++++++++++
>  4 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
> index 767df69b7f..16ab1a336f 100644
> --- a/doc/ffmpeg.texi
> +++ b/doc/ffmpeg.texi
> @@ -1633,6 +1633,8 @@ it may cause packet loss.
>  It is useful for when flow speed of output packets is important, such 
> as live streaming.
>  @item -re (@emph{input})
>  Read input at native frame rate. This is equivalent to setting 
> @code{-readrate 1}.
> +@item -irb @var{seconds}
> +Set an initial read burst time, in seconds, after which any specified 
> readrate will be enforced.
>  @item -vsync @var{parameter} (@emph{global})
>  @itemx -fps_mode[:@var{stream_specifier}] @var{parameter} 
> (@emph{output,per-stream})
>  Set video sync method / framerate mode. vsync is applied to all 
> output video streams
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index e7384f052a..e4697c8772 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -3768,6 +3768,7 @@ static int get_input_packet(InputFile *f, 
> AVPacket **pkt)
>                                (f->start_time != AV_NOPTS_VALUE ? 
> f->start_time : 0)
>                               );
>          float scale = f->rate_emu ? 1.0 : f->readrate;
> +        int64_t burst_until = AV_TIME_BASE * f->initial_read_burst;
>          for (i = 0; i < f->nb_streams; i++) {
>              InputStream *ist = input_streams[f->ist_index + i];
>              int64_t stream_ts_offset, pts, now;
> @@ -3775,7 +3776,7 @@ static int get_input_packet(InputFile *f, 
> AVPacket **pkt)
>              stream_ts_offset = FFMAX(ist->first_dts != AV_NOPTS_VALUE 
> ? ist->first_dts : 0, file_start);
>              pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
>              now = (av_gettime_relative() - ist->start) * scale + 
> stream_ts_offset;
> -            if (pts > now)
> +            if (pts - burst_until > now)
>                  return AVERROR(EAGAIN);
>          }
>      }
> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
> index 391a35cf50..aa079ab3e9 100644
> --- a/fftools/ffmpeg.h
> +++ b/fftools/ffmpeg.h
> @@ -116,6 +116,7 @@ typedef struct OptionsContext {
>      int loop;
>      int rate_emu;
>      float readrate;
> +    double initial_read_burst;
>      int accurate_seek;
>      int thread_queue_size;
>      int input_sync_ref;
> @@ -422,6 +423,7 @@ typedef struct InputFile {
>      int nb_streams_warn;  /* number of streams that the user was 
> warned of */
>      int rate_emu;
>      float readrate;
> +    double initial_read_burst;
>      int accurate_seek;
>       AVPacket *pkt;
> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> index 6e18a4a23e..57aa4929fa 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -1378,6 +1378,16 @@ static int open_input_file(OptionsContext *o, 
> const char *filename)
>          f->rate_emu = 0;
>      }
>  +    f->initial_read_burst = o->initial_read_burst ? 
> o->initial_read_burst : 0.0;
> +    if (f->initial_read_burst < 0.0) {
> +        av_log(NULL, AV_LOG_ERROR, "Option -irb for Input #%d is 
> %0.3f; it must be non-negative.\n", nb_input_files, 
> f->initial_read_burst);
> +        exit_program(1);
> +    }
> +    if ((!f->readrate && !f->rate_emu) && f->initial_read_burst) {
> +        av_log(NULL, AV_LOG_WARNING, "Option -irb ignored since 
> neither -readrate nor -re were given\n");
> +        f->initial_read_burst = 0;
> +    }
> +
>      f->pkt = av_packet_alloc();
>      if (!f->pkt)
>          exit_program(1);
> @@ -3734,6 +3744,9 @@ const OptionDef options[] = {
>      { "readrate",       HAS_ARG | OPT_FLOAT | OPT_OFFSET |
>                          OPT_EXPERT | OPT_INPUT,                      
> { .off = OFFSET(readrate) },
>          "read input at specified rate", "speed" },
> +    { "irb",            HAS_ARG | OPT_DOUBLE | OPT_OFFSET |
> +                        OPT_EXPERT | OPT_INPUT,                      
> { .off = OFFSET(initial_read_burst) },
> +        "The initial amount of input to burst read before imposing 
> any readrate", "seconds" },
>      { "target",         HAS_ARG | OPT_PERFILE | OPT_OUTPUT,          
> { .func_arg = opt_target },
>          "specify target file type (\"vcd\", \"svcd\", \"dvd\", \"dv\" 
> or \"dv50\" "
>          "with optional prefixes \"pal-\", \"ntsc-\" or \"film-\")", 
> "type" },