[FFmpeg-devel] [PATCH v2] avformat/movenc: split empty text sample when duration overflow

[Jun Li]

Fix #7637
One empty/end sample is created and inserted between two caption lines when there is a gap.
This patch is to split the sample into multiple ones when its duration is too long (>= INT_MAX).
---
 libavformat/movenc.c                          | 24 ++++++++++++++-----
 tests/fate/subtitles.mak                      |  6 +++++
 tests/ref/fate/binsub-movtextenc-long-dur     |  1 +
 .../fate/binsub-movtextenc-long-dur-timebase  |  1 +
 4 files changed, 26 insertions(+), 6 deletions(-)
 create mode 100644 tests/ref/fate/binsub-movtextenc-long-dur
 create mode 100644 tests/ref/fate/binsub-movtextenc-long-dur-timebase

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index edddfeeb00..aeb7de351f 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -5746,7 +5746,8 @@ static int mov_write_packet(AVFormatContext *s, AVPacket *pkt)
          *
          * 2) For each subtitle track, check if the current packet's
          * dts is past the duration of the last subtitle sample. If
-         * so, we now need to write an end sample for that subtitle.
+         * so, we now need to write one or multiple end samples for
+         * that subtitle.
          *
          * This must be done conditionally to allow for subtitles that
          * immediately replace each other, in which case an end sample
@@ -5760,11 +5761,22 @@ static int mov_write_packet(AVFormatContext *s, AVPacket *pkt)
             int ret;
 
             if (trk->par->codec_id == AV_CODEC_ID_MOV_TEXT &&
-                trk->track_duration < pkt->dts &&
-                (trk->entry == 0 || !trk->last_sample_is_subtitle_end)) {
-                ret = mov_write_subtitle_end_packet(s, i, trk->track_duration);
-                if (ret < 0) return ret;
-                trk->last_sample_is_subtitle_end = 1;
+                trk->track_duration < pkt->dts) {
+                int max_duration = INT_MAX - 1;
+                if (trk->entry == 0 || !trk->last_sample_is_subtitle_end) {
+                    ret = mov_write_subtitle_end_packet(s, i, trk->track_duration);
+                    if (ret < 0) return ret;
+                    trk->last_sample_is_subtitle_end = 1;
+                }
+                if (trk->last_sample_is_subtitle_end &&
+                    pkt->dts - trk->track_duration > max_duration) {
+                    int64_t dts = trk->track_duration;
+                    while(pkt->dts - dts > max_duration) {
+                        dts += max_duration;
+                        ret = mov_write_subtitle_end_packet(s, i, dts);
+                        if (ret < 0) return ret;
+                    }
+                }
             }
         }
 
diff --git a/tests/fate/subtitles.mak b/tests/fate/subtitles.mak
index 0042902161..59055e975c 100644
--- a/tests/fate/subtitles.mak
+++ b/tests/fate/subtitles.mak
@@ -34,6 +34,12 @@ fate-sub-movtext: CMD = fmtstdout ass -i $(TARGET_SAMPLES)/sub/MovText_capabilit
 FATE_SUBTITLES-$(call ENCDEC, MOVTEXT, MOV) += fate-binsub-movtextenc
 fate-binsub-movtextenc: CMD = md5 -i $(TARGET_SAMPLES)/sub/MovText_capability_tester.mp4 -map 0 -scodec mov_text -f mp4 -flags +bitexact -fflags +bitexact -movflags frag_keyframe+empty_moov
 
+FATE_SUBTITLES-$(call ENCDEC, MOVTEXT, MOV) += fate-binsub-movtextenc-long-dur
+fate-binsub-movtextenc-long-dur: CMD = md5 -i $(TARGET_SAMPLES)/sub/WebVTT_movtext_long_dur.vtt -map 0 -scodec mov_text -f mp4 -flags +bitexact -fflags +bitexact -movflags empty_moov
+
+FATE_SUBTITLES-$(call ENCDEC, MOVTEXT, MOV) += fate-binsub-movtextenc-long-dur-timebase
+fate-binsub-movtextenc-long-dur-timebase: CMD = md5 -i $(TARGET_SAMPLES)/sub/WebVTT_movtext_long_dur.vtt -map 0 -scodec mov_text -time_base 1000 -f mp4 -flags +bitexact -fflags +bitexact -movflags empty_moov
+
 FATE_SUBTITLES_ASS-$(call DEMDEC, MPL2, MPL2) += fate-sub-mpl2
 fate-sub-mpl2: CMD = fmtstdout ass -i $(TARGET_SAMPLES)/sub/MPL2_capability_tester.txt
 
diff --git a/tests/ref/fate/binsub-movtextenc-long-dur b/tests/ref/fate/binsub-movtextenc-long-dur
new file mode 100644
index 0000000000..4db0be514b
--- /dev/null
+++ b/tests/ref/fate/binsub-movtextenc-long-dur
@@ -0,0 +1 @@
+043848a72c3ae75744115fe8d06c8bf1
diff --git a/tests/ref/fate/binsub-movtextenc-long-dur-timebase b/tests/ref/fate/binsub-movtextenc-long-dur-timebase
new file mode 100644
index 0000000000..14b2f0167b
--- /dev/null
+++ b/tests/ref/fate/binsub-movtextenc-long-dur-timebase
@@ -0,0 +1 @@
+043848a72c3ae75744115fe8d06c8bf1
\ No newline at end of file
-- 
2.17.1