[FFmpeg-devel] [PATCH 3/3] ffmpeg: respect AV_CODEC_CAP_SINGLE_SUB_RECT

[Ridley Combs]

> On Feb 21, 2023, at 01:45, Nicolas George <george at nsup.org> wrote:
> 
> rcombs (12023-02-20):
>> Fixes ASS output when multiple rects are present.
>> ---
>> fftools/ffmpeg.c | 28 ++++++++++++++++++----------
>> 1 file changed, 18 insertions(+), 10 deletions(-)
> 
> Does this not belong to the framework?

I don't see a way it could be? avcodec_encode_subtitle takes an AVSubtitle and writes to a single caller-provided buffer; there's no way for it to generate multiple outputs for a single input.

> 
>> 
>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
>> index 9884e0c6c6..23eac52438 100644
>> --- a/fftools/ffmpeg.c
>> +++ b/fftools/ffmpeg.c
>> @@ -1021,6 +1021,7 @@ static void do_subtitle_out(OutputFile *of,
>>     AVCodecContext *enc;
>>     AVPacket *pkt = ost->pkt;
>>     int64_t pts;
>> +    int single_rect;
>> 
>>     if (sub->pts == AV_NOPTS_VALUE) {
>>         av_log(ost, AV_LOG_ERROR, "Subtitle packets must have a pts\n");
>> @@ -1031,11 +1032,15 @@ static void do_subtitle_out(OutputFile *of,
>> 
>>     enc = ost->enc_ctx;
>> 
>> +    single_rect = !!(enc->codec->capabilities & AV_CODEC_CAP_SINGLE_SUB_RECT);
>> +
>>     /* Note: DVB subtitle need one packet to draw them and one other
>>        packet to clear them */
>>     /* XXX: signal it in the codec context ? */
>>     if (enc->codec_id == AV_CODEC_ID_DVB_SUBTITLE)
>>         nb = 2;
>> +    else if (single_rect)
>> +        nb = FFMAX(sub->num_rects, 1);
>>     else
>>         nb = 1;
>> 
>> @@ -1044,7 +1049,7 @@ static void do_subtitle_out(OutputFile *of,
>>     if (output_files[ost->file_index]->start_time != AV_NOPTS_VALUE)
>>         pts -= output_files[ost->file_index]->start_time;
>>     for (i = 0; i < nb; i++) {
>> -        unsigned save_num_rects = sub->num_rects;
>> +        AVSubtitle local_sub = *sub;
>> 
>>         if (!check_recording_time(ost, pts, AV_TIME_BASE_Q))
>>             return;
>> @@ -1053,19 +1058,22 @@ static void do_subtitle_out(OutputFile *of,
>>         if (ret < 0)
>>             report_and_exit(AVERROR(ENOMEM));
>> 
>> -        sub->pts = pts;
>> +        local_sub.pts = pts;
>>         // start_display_time is required to be 0
>> -        sub->pts               += av_rescale_q(sub->start_display_time, (AVRational){ 1, 1000 }, AV_TIME_BASE_Q);
>> -        sub->end_display_time  -= sub->start_display_time;
>> -        sub->start_display_time = 0;
>> -        if (i == 1)
>> -            sub->num_rects = 0;
>> +        local_sub.pts               += av_rescale_q(sub->start_display_time, (AVRational){ 1, 1000 }, AV_TIME_BASE_Q);
>> +        local_sub.end_display_time  -= sub->start_display_time;
>> +        local_sub.start_display_time = 0;
>> +
>> +        if (enc->codec_id == AV_CODEC_ID_DVB_SUBTITLE && i == 1)
>> +            local_sub.num_rects = 0;
>> +        else if (single_rect && sub->num_rects > 0) {
>> +            local_sub.num_rects = 1;
>> +            local_sub.rects += i;
>> +        }
>> 
>>         ost->frames_encoded++;
>> 
>> -        subtitle_out_size = avcodec_encode_subtitle(enc, pkt->data, pkt->size, sub);
>> -        if (i == 1)
>> -            sub->num_rects = save_num_rects;
>> +        subtitle_out_size = avcodec_encode_subtitle(enc, pkt->data, pkt->size, &local_sub);
>>         if (subtitle_out_size < 0) {
>>             av_log(ost, AV_LOG_FATAL, "Subtitle encoding failed\n");
>>             exit_program(1);
> 
> Regards,
> 
> -- 
>  Nicolas George
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