ffmpeg: add video heartbeat capability to fix_sub_duration

Splits the currently handled subtitle at random access point
packets that can be configured to follow a specific output stream.
Currently only subtitle streams which are directly mapped into the
same output in which the heartbeat stream resides are affected.

This way the subtitle - which is known to be shown at this time
can be split and passed to muxer before its full duration is
yet known. This is also a drawback, as this essentially outputs
multiple subtitles from a single input subtitle that continues
over multiple random access points. Thus this feature should not
be utilized in cases where subtitle output latency does not matter.

Co-authored-by: Andrzej Nadachowski <andrzej.nadachowski@24i.com>
Co-authored-by: Bernard Boulay <bernard.boulay@24i.com>

Signed-off-by: Jan Ekström <jan.ekstrom@24i.com>

2 files changed, 63 insertions, 0 deletions

diff --git a/tests/fate/ffmpeg.mak b/tests/fate/ffmpeg.mak
index d87639c596..0f33c2a0ed 100644
--- a/tests/fate/ffmpeg.mak
+++ b/tests/fate/ffmpeg.mak
@@ -117,6 +117,21 @@ fate-ffmpeg-fix_sub_duration: CMD = fmtstdout srt -fix_sub_duration \
   -real_time 1 -f lavfi \
   -i "movie=$(TARGET_SAMPLES)/sub/Closedcaption_rollup.m2v[out0+subcc]"
 
+# Basic test for fix_sub_duration_heartbeat, which causes a buffered subtitle
+# to be pushed out when a video keyframe is received from an encoder.
+FATE_SAMPLES_FFMPEG-$(call FILTERDEMDECENCMUX, MOVIE, MPEGVIDEO, \
+                           MPEG2VIDEO, SUBRIP, SRT, LAVFI_INDEV  \
+                           MPEGVIDEO_PARSER CCAPTION_DECODER \
+                           MPEG2VIDEO_ENCODER NULL_MUXER PIPE_PROTOCOL) \
+                           += fate-ffmpeg-fix_sub_duration_heartbeat
+fate-ffmpeg-fix_sub_duration_heartbeat: CMD = fmtstdout srt -fix_sub_duration \
+  -real_time 1 -f lavfi \
+  -i "movie=$(TARGET_SAMPLES)/sub/Closedcaption_rollup.m2v[out0+subcc]" \
+  -map 0:v  -map 0:s -fix_sub_duration_heartbeat:v:0 \
+  -c:v mpeg2video -b:v 2M -g 30 -sc_threshold 1000000000 \
+  -c:s srt \
+  -f null -
+
 FATE_STREAMCOPY-$(call REMUX, MP4 MOV, EAC3_DEMUXER) += fate-copy-trac3074
 fate-copy-trac3074: CMD = transcode eac3 $(TARGET_SAMPLES)/eac3/csi_miami_stereo_128_spx.eac3\
                      mp4 "-codec copy -map 0" "-codec copy"
diff --git a/tests/ref/fate/ffmpeg-fix_sub_duration_heartbeat b/tests/ref/fate/ffmpeg-fix_sub_duration_heartbeat
new file mode 100644
index 0000000000..957a410921
--- /dev/null
+++ b/tests/ref/fate/ffmpeg-fix_sub_duration_heartbeat
@@ -0,0 +1,48 @@
+1
+00:00:00,968 --> 00:00:01,001
+<font face="Monospace">{\an7}(</font>
+
+2
+00:00:01,001 --> 00:00:01,168
+<font face="Monospace">{\an7}(</font>
+
+3
+00:00:01,168 --> 00:00:01,368
+<font face="Monospace">{\an7}(<i> inaudibl</i></font>
+
+4
+00:00:01,368 --> 00:00:01,568
+<font face="Monospace">{\an7}(<i> inaudible radio chat</i></font>
+
+5
+00:00:01,568 --> 00:00:02,002
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )</font>
+
+6
+00:00:02,002 --> 00:00:03,003
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )</font>
+
+7
+00:00:03,003 --> 00:00:03,103
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )</font>
+
+8
+00:00:03,103 --> 00:00:03,303
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>></font>
+
+9
+00:00:03,303 --> 00:00:03,503
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>> Safety rema</font>
+
+10
+00:00:03,504 --> 00:00:03,704
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>> Safety remains our numb</font>
+
+11
+00:00:03,704 --> 00:00:04,004
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>> Safety remains our number one</font>
+