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

[Pavel Koshevoy]

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