tests: add test for ffmpeg's fix_sub_duration feature

This long-existing feature calculates subtitle durations by keeping
it around until the following subtitle is decoded, and then utilizes
the following subtitle's pts as the end point of the previous one.

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

tests/fate/ffmpeg.mak

@@ -100,6 +100,17 @@ FATE_SAMPLES_FFMPEG-$(call ALLYES, FILE_PROTOCOL LAVFI_INDEV RAWVIDEO_DEMUXER \
 fate-shortest: tests/data/vsynth_lena.yuv
 fate-shortest: CMD = framecrc -auto_conversion_filters -f lavfi -i "sine=3000:d=10" -f lavfi -i "sine=1000:d=1" -sws_flags +accurate_rnd+bitexact -fflags +bitexact -flags +bitexact -idct simple -f rawvideo -s 352x288 -pix_fmt yuv420p -i $(TARGET_PATH)/tests/data/vsynth_lena.yuv -filter_complex "[0:a:0][1:a:0]amix=inputs=2[audio]" -map 2:v:0 -map "[audio]" -sws_flags +accurate_rnd+bitexact -fflags +bitexact -flags +bitexact -idct simple -dct fastint -qscale 10 -threads 1 -c:v mpeg4 -c:a ac3_fixed -shortest
 
+# Basic test for fix_sub_duration, which calculates duration based on the
+# following subtitle's pts.
+FATE_SAMPLES_FFMPEG-$(call ALLYES, LAVFI_INDEV MOVIE_FILTER FILE_PROTOCOL \
+                                   PIPE_PROTOCOL MPEGVIDEO_DEMUXER \
+                                   MPEG2VIDEO_DECODER CCAPTION_DECODER \
+                                   SUBRIP_ENCODER SRT_MUXER) \
+                           += fate-ffmpeg-fix_sub_duration
+fate-ffmpeg-fix_sub_duration: CMD = fmtstdout srt -fix_sub_duration \
+  -real_time 1 -f lavfi \
+  -i "movie=$(TARGET_SAMPLES)/sub/Closedcaption_rollup.m2v[out0+subcc]"
+
 FATE_STREAMCOPY-$(call ALLYES, EAC3_DEMUXER MOV_MUXER) += fate-copy-trac3074
 fate-copy-trac3074: $(SAMPLES)/eac3/csi_miami_stereo_128_spx.eac3
 fate-copy-trac3074: CMD = transcode eac3 $(TARGET_SAMPLES)/eac3/csi_miami_stereo_128_spx.eac3\

tests/ref/fate/ffmpeg-fix_sub_duration

@@ -0,0 +1,31 @@
+1
+00:00:00,968 --> 00:00:01,168
+<font face="Monospace">{\an7}(</font>
+
+2
+00:00:01,168 --> 00:00:01,368
+<font face="Monospace">{\an7}(<i> inaudibl</i></font>
+
+3
+00:00:01,368 --> 00:00:01,568
+<font face="Monospace">{\an7}(<i> inaudible radio chat</i></font>
+
+4
+00:00:01,568 --> 00:00:03,103
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )</font>
+
+5
+00:00:03,103 --> 00:00:03,303
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>></font>
+
+6
+00:00:03,303 --> 00:00:03,503
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>> Safety rema</font>
+
+7
+00:00:03,504 --> 00:00:03,704
+<font face="Monospace">{\an7}(<i> inaudible radio chatter</i> )
+>> Safety remains our numb</font>
+