[FFmpeg-devel] [PATCH] ffmpeg_demux: add option readrate_catchup
Gyan Doshi
ffmpeg at gyani.pro
Sun Feb 23 09:36:07 EET 2025
On 2025-02-18 03:16 pm, Gyan Doshi wrote:
> At present, if reading from a readrate-limited input is stalled,
> then upon resumption, ffmpeg will read the input without any
> throttle till the average readrate matches the specified readrate.
>
> This new option allows to set a speed limit when reading is resumed
> until the average readrate matches the primary readrate.
>
> Fixes #11469
Plan to push tomorrow.
Regards,
Gyan
> ---
> doc/ffmpeg.texi | 5 ++++
> fftools/ffmpeg.h | 1 +
> fftools/ffmpeg_demux.c | 62 ++++++++++++++++++++++++++++++++++++------
> fftools/ffmpeg_opt.c | 3 ++
> 4 files changed, 63 insertions(+), 8 deletions(-)
>
> diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
> index da6549f043..fca220a334 100644
> --- a/doc/ffmpeg.texi
> +++ b/doc/ffmpeg.texi
> @@ -2325,6 +2325,11 @@ Read input at native frame rate. This is equivalent to setting @code{-readrate 1
> @item -readrate_initial_burst @var{seconds}
> Set an initial read burst time, in seconds, after which @option{-re/-readrate}
> will be enforced.
> + at item -readrate_catchup @var{speed} (@emph{input})
> +If either the input or output is blocked leading to actual read speed falling behind the
> +specified readrate, then this rate takes effect till the input catches up with the
> +specified readrate. Must not be lower than the primary readrate.
> +
> @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.h b/fftools/ffmpeg.h
> index 9439be0f41..c37a085029 100644
> --- a/fftools/ffmpeg.h
> +++ b/fftools/ffmpeg.h
> @@ -163,6 +163,7 @@ typedef struct OptionsContext {
> int loop;
> int rate_emu;
> float readrate;
> + float readrate_catchup;
> double readrate_initial_burst;
> int accurate_seek;
> int thread_queue_size;
> diff --git a/fftools/ffmpeg_demux.c b/fftools/ffmpeg_demux.c
> index 5ff75eed1a..4a4a134afa 100644
> --- a/fftools/ffmpeg_demux.c
> +++ b/fftools/ffmpeg_demux.c
> @@ -94,6 +94,12 @@ typedef struct DemuxStream {
> uint64_t nb_packets;
> // combined size of all the packets read
> uint64_t data_size;
> + // latest wallclock time at which packet reading resumed after a stall - used for readrate
> + int64_t resume_wc;
> + // timestamp of first packet sent after the latest stall - used for readrate
> + int64_t resume_pts;
> + // measure of how far behind packet reading is against spceified readrate
> + int64_t lag;
> } DemuxStream;
>
> typedef struct Demuxer {
> @@ -127,6 +133,7 @@ typedef struct Demuxer {
>
> float readrate;
> double readrate_initial_burst;
> + float readrate_catchup;
>
> Scheduler *sch;
>
> @@ -495,16 +502,42 @@ static void readrate_sleep(Demuxer *d)
> (f->start_time_effective != AV_NOPTS_VALUE ? f->start_time_effective * !start_at_zero : 0) +
> (f->start_time != AV_NOPTS_VALUE ? f->start_time : 0)
> );
> - int64_t burst_until = AV_TIME_BASE * d->readrate_initial_burst;
> + int64_t initial_burst = AV_TIME_BASE * d->readrate_initial_burst;
> + int resume_warn;
> +
> for (int i = 0; i < f->nb_streams; i++) {
> InputStream *ist = f->streams[i];
> DemuxStream *ds = ds_from_ist(ist);
> - int64_t stream_ts_offset, pts, now;
> + int64_t stream_ts_offset, pts, now, wc_elapsed, elapsed, lag, max_pts, limit_pts;
> +
> + if (ds->discard) continue;
> +
> stream_ts_offset = FFMAX(ds->first_dts != AV_NOPTS_VALUE ? ds->first_dts : 0, file_start);
> pts = av_rescale(ds->dts, 1000000, AV_TIME_BASE);
> - now = (av_gettime_relative() - d->wallclock_start) * d->readrate + stream_ts_offset;
> - if (pts - burst_until > now)
> - av_usleep(pts - burst_until - now);
> + now = av_gettime_relative();
> + wc_elapsed = now - d->wallclock_start;
> + max_pts = stream_ts_offset + initial_burst + wc_elapsed * d->readrate;
> + lag = FFMAX(max_pts - pts, 0);
> + if ( (!ds->lag && lag > 0.3 * AV_TIME_BASE) || ( lag > ds->lag + 0.3 * AV_TIME_BASE) ) {
> + ds->lag = lag;
> + ds->resume_wc = now;
> + ds->resume_pts = pts;
> + av_log_once(ds, AV_LOG_WARNING, AV_LOG_DEBUG, &resume_warn,
> + "Resumed reading at pts %0.3f with rate %0.3f after a lag of %0.3fs\n",
> + (float)pts/AV_TIME_BASE, d->readrate_catchup, (float)lag/AV_TIME_BASE);
> + }
> + if (ds->lag && !lag)
> + ds->lag = ds->resume_wc = ds->resume_pts = 0;
> + if (ds->resume_wc) {
> + elapsed = now - ds->resume_wc;
> + limit_pts = ds->resume_pts + elapsed * d->readrate_catchup;
> + } else {
> + elapsed = wc_elapsed;
> + limit_pts = max_pts;
> + }
> +
> + if (pts > limit_pts)
> + av_usleep(pts - limit_pts);
> }
> }
>
> @@ -1859,9 +1892,22 @@ int ifile_open(const OptionsContext *o, const char *filename, Scheduler *sch)
> d->readrate_initial_burst);
> return AVERROR(EINVAL);
> }
> - } else if (o->readrate_initial_burst) {
> - av_log(d, AV_LOG_WARNING, "Option -readrate_initial_burst ignored "
> - "since neither -readrate nor -re were given\n");
> + d->readrate_catchup = o->readrate_catchup ? o->readrate_catchup : d->readrate;
> + if (d->readrate_catchup < d->readrate) {
> + av_log(d, AV_LOG_ERROR,
> + "Option -readrate_catchup is %0.3f; it must be at least equal to %0.3f.\n",
> + d->readrate_catchup, d->readrate);
> + return AVERROR(EINVAL);
> + }
> + } else {
> + if (o->readrate_initial_burst) {
> + av_log(d, AV_LOG_WARNING, "Option -readrate_initial_burst ignored "
> + "since neither -readrate nor -re were given\n");
> + }
> + if (o->readrate_catchup) {
> + av_log(d, AV_LOG_WARNING, "Option -readrate_catchup ignored "
> + "since neither -readrate nor -re were given\n");
> + }
> }
>
> /* Add all the streams from the given input file to the demuxer */
> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> index 3c0c682594..27a9fc9e42 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -1639,6 +1639,9 @@ const OptionDef options[] = {
> { "readrate_initial_burst", OPT_TYPE_DOUBLE, OPT_OFFSET | OPT_EXPERT | OPT_INPUT,
> { .off = OFFSET(readrate_initial_burst) },
> "The initial amount of input to burst read before imposing any readrate", "seconds" },
> + { "readrate_catchup", OPT_TYPE_FLOAT, OPT_OFFSET | OPT_EXPERT | OPT_INPUT,
> + { .off = OFFSET(readrate_catchup) },
> + "Temporary readrate used to catch up if an input lags behind the specified readrate", "speed" },
> { "target", OPT_TYPE_FUNC, OPT_FUNC_ARG | OPT_PERFILE | OPT_EXPERT | OPT_OUTPUT,
> { .func_arg = opt_target },
> "specify target file type (\"vcd\", \"svcd\", \"dvd\", \"dv\" or \"dv50\" "
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