[FFmpeg-devel] [PATCH v2] avcodec/ccaption_dec: Make real-time latency configurable

[Pavel Koshevoy]

On Mon, Jun 14, 2021 at 10:04 AM Paul B Mahol <onemda at gmail.com> wrote:

> On Sun, Jun 13, 2021 at 11:50 PM Pavel Koshevoy <pkoshevoy at gmail.com>
> wrote:
>
> > On Sat, Jun 5, 2021 at 11:40 AM Pavel Koshevoy <pkoshevoy at gmail.com>
> > wrote:
> >
> > > Un-hardcode the 200ms minimum latency between emitting subtitle events
> > > so that those that wish to receive a subtitle event for every screen
> > > change could do so.
> > >
> > > The problem with delaying realtime output by any amount is that it is
> > > unknown when the next byte pair that would trigger output will happen.
> > > It may be within 200ms, or it may be several seconds later -- that's
> > > not realtime at all.
> > > ---
> > >  libavcodec/ccaption_dec.c | 4 +++-
> > >  libavcodec/version.h      | 2 +-
> > >  2 files changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
> > > index de05d037a8..27c61527f6 100644
> > > --- a/libavcodec/ccaption_dec.c
> > > +++ b/libavcodec/ccaption_dec.c
> > > @@ -238,6 +238,7 @@ struct Screen {
> > >  typedef struct CCaptionSubContext {
> > >      AVClass *class;
> > >      int real_time;
> > > +    int real_time_latency_msec;
> > >      int data_field;
> > >      struct Screen screen[2];
> > >      int active_screen;
> > > @@ -906,7 +907,7 @@ static int decode(AVCodecContext *avctx, void
> *data,
> > > int *got_sub, AVPacket *avp
> > >      }
> > >
> > >      if (ctx->real_time && ctx->screen_touched &&
> > > -        sub->pts > ctx->last_real_time + av_rescale_q(200, ms_tb,
> > > AV_TIME_BASE_Q)) {
> > > +        sub->pts >= ctx->last_real_time +
> > > av_rescale_q(ctx->real_time_latency_msec, ms_tb, AV_TIME_BASE_Q)) {
> > >          ctx->last_real_time = sub->pts;
> > >          ctx->screen_touched = 0;
> > >
> > > @@ -927,6 +928,7 @@ static int decode(AVCodecContext *avctx, void
> *data,
> > > int *got_sub, AVPacket *avp
> > >  #define SD AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_DECODING_PARAM
> > >  static const AVOption options[] = {
> > >      { "real_time", "emit subtitle events as they are decoded for
> > > real-time display", OFFSET(real_time), AV_OPT_TYPE_BOOL, { .i64 = 0 },
> 0,
> > > 1, SD },
> > > +    { "real_time_latency_msec", "minimum elapsed time between emitting
> > > real-time subtitle events", OFFSET(real_time_latency_msec),
> > > AV_OPT_TYPE_INT, { .i64 = 200 }, 0, 500, SD },
> > >      { "data_field", "select data field", OFFSET(data_field),
> > > AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, SD, "data_field" },
> > >      { "auto",   "pick first one that appears", 0, AV_OPT_TYPE_CONST, {
> > > .i64 =-1 }, 0, 0, SD, "data_field" },
> > >      { "first",  NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 0 }, 0, 0, SD,
> > > "data_field" },
> > > diff --git a/libavcodec/version.h b/libavcodec/version.h
> > > index 48165b9ac4..5b1e9e77f3 100644
> > > --- a/libavcodec/version.h
> > > +++ b/libavcodec/version.h
> > > @@ -29,7 +29,7 @@
> > >
> > >  #define LIBAVCODEC_VERSION_MAJOR  59
> > >  #define LIBAVCODEC_VERSION_MINOR   1
> > > -#define LIBAVCODEC_VERSION_MICRO 100
> > > +#define LIBAVCODEC_VERSION_MICRO 101
> > >
> > >  #define LIBAVCODEC_VERSION_INT
> > AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
> > >
> >  LIBAVCODEC_VERSION_MINOR, \
> > > --
> > > 2.26.2
> > >
> > >
> >
> > Ping.  If there are no objections may this be applied?
> >
> >
> Do you have power to apply it?
>
>
Yes, I have git access, but I'm not the maintainer of
libavcodec/ccaption_dec.c

Pavel.