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

[Jun Li]

On Sun, Sep 8, 2019 at 5:51 PM Jun Li <junli1026 at gmail.com> wrote:

> 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
>
>
Version 2 addressed the feedback from Jan, adding fate test.
The attachment is the sample file for the tests. I will send it to
samples-request at ffmpeg.org if this patch is approved.

-Jun
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