[FFmpeg-devel] [PATCH v1] 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 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

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;
+                    }
+                }
             }
         }
 
-- 
2.17.1