[FFmpeg-devel] [PATCH 5/5] avformat/matroskaenc: update AV1 support

[James Almer]

On 7/30/2018 2:03 AM, Steve Lhomme wrote:
> On 26/07/2018 03:11, James Almer wrote:
>> Make sure to not write forbidden OBUs to CodecPrivate, and do the same
>> with
>> unnecessary OBUs for packets.
> 
> Does this include reordering the OBUs ? The first one must be the
> Sequence Header OBU. Also it must be the only one of that kind.

No, it doesn't. I can make that change, but why does it matter if it's
the first? Why can't a metadata OBU be before a Seq Header? isobmff
doesn't care what's first, only what's in.
A parser is currently forced to know how to read OBUs anyway, and it
could just skip any metadata obu before the sequence header.

For that matter, i do agree with
https://github.com/AOMediaCodec/av1-isobmff/issues/7#issuecomment-406257234
and
https://github.com/AOMediaCodec/av1-isobmff/issues/46#issuecomment-406516226
that perhaps av1C should, much like hvcC, avcC and in it's own way also
vpcC, contain a bunch of header bytes listing some basic information
(and therefore the entire thing, sans atom size and fourcc, be included
in CodecPrivate verbatim). Things like profile, level, and maybe number
of OBUs, before the raw OBUs.
As an extra benefit than simply removing the requirement for demuxers to
parse OBUs that may even only be in sample data just to see if the file
can be decoded (firing up a hardware decoder can be expensive), it would
also give us a way to identify the source of the bitstream (mp4/mkv vs
ivf/raw/annexb/etc), for example for the purpose of inserting the
extradata Seq Header if not present on key frames (Matroska allows to
remove it, but isobmff in section 2.5 seems to want a sync sample to be
a fully compliant RAP without the need of extradata obus, despite the
description in section 2.4.4), achieved by writing and using an
av1_mp4tolobf bsf or similar, which would then be included where needed
instead of the naive dump_extradata one from patch 2/5 of this set, for
example.

> 
>>
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>   libavformat/matroskaenc.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
>> index b7ff1950d3..816ddd059a 100644
>> --- a/libavformat/matroskaenc.c
>> +++ b/libavformat/matroskaenc.c
>> @@ -21,6 +21,7 @@
>>     #include <stdint.h>
>>   +#include "av1.h"
>>   #include "avc.h"
>>   #include "hevc.h"
>>   #include "avformat.h"
>> @@ -769,6 +770,9 @@ static int
>> mkv_write_native_codecprivate(AVFormatContext *s, AVIOContext *pb,
>>           ff_isom_write_hvcc(dyn_cp, par->extradata,
>>                              par->extradata_size, 0);
>>           return 0;
>> +    case AV_CODEC_ID_AV1:
>> +        return ff_isom_write_av1c(dyn_cp, par->extradata,
>> +                                  par->extradata_size);
>>       case AV_CODEC_ID_ALAC:
>>           if (par->extradata_size < 36) {
>>               av_log(s, AV_LOG_ERROR,
>> @@ -2120,6 +2124,8 @@ static void mkv_write_block(AVFormatContext *s,
>> AVIOContext *pb,
>>                (AV_RB24(par->extradata) == 1 ||
>> AV_RB32(par->extradata) == 1))
>>           /* extradata is Annex B, assume the bitstream is too and
>> convert it */
>>           ff_hevc_annexb2mp4_buf(pkt->data, &data, &size, 0, NULL);
>> +    else if (par->codec_id == AV_CODEC_ID_AV1)
>> +        ff_av1_filter_obus_buf(pkt->data, &data, &size);
>>       else if (par->codec_id == AV_CODEC_ID_WAVPACK) {
>>           int ret = mkv_strip_wavpack(pkt->data, &data, &size);
>>           if (ret < 0) {
>> -- 
>> 2.18.0
>>
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> 
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