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

[Pavel Koshevoy]

On Thu, Jun 17, 2021 at 7:07 PM Pavel Koshevoy <pkoshevoy at gmail.com> wrote:

>
>
> On Sun, Jun 13, 2021 at 3:49 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?
>>
>> Thank you,
>>     Pavel.
>>
>
>
> If there are no objections I will apply and push this in 24h
>
> Thank you,
>     Pavel.
>


Bumped LIBAVCODEC_VERSION_MICRO to 102 and pushed.

Thank you,
    Pavel.