Re: [FFmpeg-devel] [PATCH 2/2] avformat/movenc: Add loop parameter to animated AVIF

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Jan 6, 2023, at 01:34, Vignesh Venkatasubramanian <vigneshv-at-google.com@ffmpeg.org> wrote:
> 
> On Thu, Jan 5, 2023 at 1:45 AM "zhilizhao(赵志立)" <quinkblack@foxmail.com> wrote:
>> 
>> 
>> 
>>> On Jan 5, 2023, at 06:16, Vignesh Venkatasubramanian <vigneshv-at-google.com@ffmpeg.org> wrote:
>>> 
>>> The HEIF specification permits specifying the looping behavior of
>>> animated sequences by using the EditList (elst) box. The track
>>> duration will be set to the total duration of all the loops (or
>>> infinite) and the duration of a single loop will be set in the edit
>>> list box.
>>> 
>>> The default behavior is to loop infinitely.
>>> 
>>> Compliance verification:
>>> * This was added in libavif recently [1] and the files produced by
>>> ffmpeg after this change have EditList boxes similar to the ones
>>> produced by libavif (and avifdec is able to parse the loop count as
>>> intended).
>>> * ComplianceWarden is ok with the produced files.
>>> * Chrome is able to play back the produced files.
>>> 
>>> Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
>>> ---
>>> libavformat/movenc.c | 35 +++++++++++++++++++++++++++++++----
>>> libavformat/movenc.h |  1 +
>>> 2 files changed, 32 insertions(+), 4 deletions(-)
>>> 
>>> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
>>> index 36c76f7f60..8d31317838 100644
>>> --- a/libavformat/movenc.c
>>> +++ b/libavformat/movenc.c
>>> @@ -3287,7 +3287,7 @@ static int mov_write_tkhd_tag(AVIOContext *pb, MOVMuxContext *mov,
>>>    int64_t duration = av_rescale_rnd(calc_pts_duration(mov, track),
>>>                                      mov->movie_timescale, track->timescale,
>>>                                      AV_ROUND_UP);
>>> -    int version = duration < INT32_MAX ? 0 : 1;
>>> +    int version;
>>>    int flags   = MOV_TKHD_FLAG_IN_MOVIE;
>>>    int group   = 0;
>>> 
>>> @@ -3295,6 +3295,14 @@ static int mov_write_tkhd_tag(AVIOContext *pb, MOVMuxContext *mov,
>>>    size_t display_matrix_size;
>>>    int       i;
>>> 
>>> +    if (mov->mode == MODE_AVIF)
>>> +        if (!mov->avif_loop_count)
>>> +            duration = INT64_MAX;
>>> +        else
>>> +            duration *= mov->avif_loop_count;
>>> +
>>> +     version = duration < INT32_MAX ? 0 : 1;
>>> +
>>>    if (st) {
>>>        if (mov->per_stream_grouping)
>>>            group = st->index;
>>> @@ -3414,7 +3422,10 @@ static int mov_write_tapt_tag(AVIOContext *pb, MOVTrack *track)
>>>    return update_size(pb, pos);
>>> }
>>> 
>>> -// This box seems important for the psp playback ... without it the movie seems to hang
>>> +// This box is written in the following cases:
>>> +//   * Seems important for the psp playback. Without it the movie seems to hang.
>>> +//   * Used for specifying the looping behavior of animated AVIF (as specified
>>> +//   in Section 9.6 of the HEIF specification ISO/IEC 23008-12).
>>> static int mov_write_edts_tag(AVIOContext *pb, MOVMuxContext *mov,
>>>                              MOVTrack *track)
>>> {
>>> @@ -3425,6 +3436,7 @@ static int mov_write_edts_tag(AVIOContext *pb, MOVMuxContext *mov,
>>>    int entry_size, entry_count, size;
>>>    int64_t delay, start_ct = track->start_cts;
>>>    int64_t start_dts = track->start_dts;
>>> +    int flags = 0;
>>> 
>>>    if (track->entry) {
>>>        if (start_dts != track->cluster[0].dts || start_ct != track->cluster[0].cts) {
>>> @@ -3440,6 +3452,17 @@ static int mov_write_edts_tag(AVIOContext *pb, MOVMuxContext *mov,
>>> 
>>>    delay = av_rescale_rnd(start_dts + start_ct, mov->movie_timescale,
>>>                           track->timescale, AV_ROUND_DOWN);
>>> +
>>> +    if (mov->mode == MODE_AVIF) {
>>> +        delay = 0;
>>> +        // Section 9.6.3 of ISO/IEC 23008-12: flags specifies repetition of the
>>> +        // edit list as follows: (flags & 1) equal to 0 specifies that the edit
>>> +        // list is not repeated, while (flags & 1) equal to 1 specifies that the
>>> +        // edit list is repeated.
>>> +        flags = mov->avif_loop_count != 1;
>>> +        start_ct = 0;
>>> +    }
>>> +
>>>    version |= delay < INT32_MAX ? 0 : 1;
>>> 
>>>    entry_size = (version == 1) ? 20 : 12;
>>> @@ -3452,7 +3475,7 @@ static int mov_write_edts_tag(AVIOContext *pb, MOVMuxContext *mov,
>>>    avio_wb32(pb, size - 8);
>>>    ffio_wfourcc(pb, "elst");
>>>    avio_w8(pb, version);
>>> -    avio_wb24(pb, 0); /* flags */
>>> +    avio_wb24(pb, flags); /* flags */
>>> 
>>>    avio_wb32(pb, entry_count);
>>>    if (delay > 0) { /* add an empty edit to delay presentation */
>>> @@ -3469,7 +3492,7 @@ static int mov_write_edts_tag(AVIOContext *pb, MOVMuxContext *mov,
>>>            avio_wb32(pb, -1);
>>>        }
>>>        avio_wb32(pb, 0x00010000);
>>> -    } else {
>>> +    } else if (mov->mode != MODE_AVIF) {
>>>        /* Avoid accidentally ending up with start_ct = -1 which has got a
>>>         * special meaning. Normally start_ct should end up positive or zero
>>>         * here, but use FFMIN in case dts is a small positive integer
>>> @@ -3670,6 +3693,9 @@ static int mov_write_trak_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContext
>>>                   "Not writing any edit list even though one would have been required\n");
>>>    }
>>> 
>>> +    if (mov->is_animated_avif)
>>> +        mov_write_edts_tag(pb, mov, track);
>>> +
>>>    if (track->tref_tag)
>>>        mov_write_tref_tag(pb, track);
>>> 
>>> @@ -7761,6 +7787,7 @@ static const AVCodecTag codec_f4v_tags[] = {
>>> 
>>> static const AVOption avif_options[] = {
>>>    { "movie_timescale", "set movie timescale", offsetof(MOVMuxContext, movie_timescale), AV_OPT_TYPE_INT, {.i64 = MOV_TIMESCALE}, 1, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM},
>>> +    { "loop", "Number of times to loop animated AVIF: 0 - infinite loop", offsetof(MOVMuxContext, avif_loop_count), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, 0 },
>> 
>> The code treat -loop 1 means playback 1 time. It can be misleading
>> to mean 2 times, playback 1 time then repeat/loop 1 time. That’s
>> how ‘-stream_loop’ option works. I’m not English native speaker,
>> I don’t know which one is correct. Better make the offset by 1
>> clear.
>> 
> 
> libavif uses the term "repetitionCount" instead of "loop" to not have
> this ambiguity.
> 
> The behavior of the "loop" parameter in this implementation is similar
> to WebP's "loop" parameter in ffmpeg (i.e.) loop means the number of
> times it will be played back (loop == 1 => 1 playback, loop == 2 => 2
> playbacks and so on).

LGTM then.

> 
>>>    { NULL },
>>> };
>>> static const AVCodecTag codec_avif_tags[] = {
>>> diff --git a/libavformat/movenc.h b/libavformat/movenc.h
>>> index c6b3313deb..e85d83abdb 100644
>>> --- a/libavformat/movenc.h
>>> +++ b/libavformat/movenc.h
>>> @@ -249,6 +249,7 @@ typedef struct MOVMuxContext {
>>>    int64_t avif_extent_pos[2];  // index 0 is YUV and 1 is Alpha.
>>>    int avif_extent_length[2];   // index 0 is YUV and 1 is Alpha.
>>>    int is_animated_avif;
>>> +    int avif_loop_count;
>>> } MOVMuxContext;
>>> 
>>> #define FF_MOV_FLAG_RTP_HINT              (1 <<  0)
>>> --
>>> 2.39.0.314.g84b9a713c41-goog
>>> 
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>> 
> 
> 
> -- 
> Vignesh
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