[FFmpeg-devel] [PATCH] avformat/matroskaenc: Write duration early during mkv_write_header

Soft Works softworkz at hotmail.com
Mon Jul 18 23:31:03 EEST 2016

Hendrik and Michael,

thanks for looking into my patch!

>>      if (!strcmp(s->oformat->name, "webm"))
>>          mkv->mode = MODE_WEBM;
>> @@ -1594,6 +1620,18 @@ static int mkv_write_header(AVFormatContext *s)
>>      mkv->duration_offset = avio_tell(pb);
>>      if (!mkv->is_live) {
>>          put_ebml_void(pb, 11);              // assumes double-precision float to be written
>The void element here is to reserve space for the duration. If you're
>actually writing a duration here, it makes no sense to keep the void
>Then you could also remove the change in write_trailer.

I incorrectly assumed that put_ebml_void would zero out the data without advancing.

> breaks fate

i'm running fate now and will submit a revised patch.

Thanks very much,


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