Re: [FFmpeg-devel] [PATCH v2 03/10] avcodec: add bitstream parser for H266/VVC

[Thomas Siedel <thomas.ff@spin-digital.com>]

On Mon, 24 Oct 2022 at 16:38, James Almer <jamrial@gmail.com> wrote:

> On 10/24/2022 11:06 AM, Thomas Siedel wrote:
> > +static int combine_au(AVCodecParserContext *ctx, AVCodecContext *avctx,
> > +                      const uint8_t **buf, int *buf_size)
> > +{
>
> This is being called only when you first assembled AUs from what's
> assumed to be raw input. When PARSER_FLAG_COMPLETE_FRAMES is set, it
> should also parse the AU for bitstream information.
>

Yes, currently, "combine_au" is only called when
PARSER_FLAG_COMPLETE_FRAMES is disabled, but I do not really understand
what the issue is here.
As far as I know, all bitstream information is parsed properly for any kind
of supported content (currently, ES, MP4, and TS are supported).
Would you happen to have an example of a use case where
PARSER_FLAG_COMPLETE_FRAMES is enabled, and the bitstream information is
needed or not parsed correctly from the current implementation?

 The current behavior is pretty similar to other codec
parser implementations like hevc, avc, and av1. Why should the vvc parser
code differ from the (default) behavior of other codecs?


> > +    VVCParserContext *s = ctx->priv_data;
> > +    CodedBitstreamFragment *pu = &s->picture_unit;
> > +    int ret;
> > +
> > +    s->cbc->log_ctx = avctx;
> > +
> > +    if (avctx->extradata_size && !s->parsed_extradata) {
> > +        s->parsed_extradata = 1;
> > +
> > +        if ((ret = ff_cbs_read(s->cbc, pu, avctx->extradata,
> avctx->extradata_size)) < 0)
>
> ff_cbs_read_extradata_from_codec()
>
> > +            av_log(avctx, AV_LOG_WARNING, "Failed to parse
> extradata.\n");
> > +
> > +        ff_cbs_fragment_reset(pu);
> > +    }
> > +    av_packet_unref(&s->last_au);
> > +    ret = parse_nal_units(ctx, *buf, *buf_size, avctx);
> > +    if (ret == 0) {
> > +        if (s->last_au.size) {
> > +            *buf = s->last_au.data;
> > +            *buf_size = s->last_au.size;
> > +        } else {
> > +            //no output
> > +            ret = 1;
> > +        }
> > +    }
> > +    s->cbc->log_ctx = NULL;
> > +    return ret;
> > +}
> > +
> > +static int vvc_parser_parse(AVCodecParserContext *ctx, AVCodecContext
> *avctx,
> > +                      const uint8_t **poutbuf, int *poutbuf_size,
> > +                      const uint8_t *buf, int buf_size)
> > +{
> > +    int next;
> > +    VVCParserContext *s = ctx->priv_data;
> > +    ParseContext *pc = &s->pc;
> > +
> > +    if (avctx->extradata && !s->parsed_extradata) {
> > +        av_log(avctx, AV_LOG_INFO, "extra data is not supported
> yet.\n");
> > +        return AVERROR_PATCHWELCOME;
> > +    }
> > +
> > +    if (ctx->flags & PARSER_FLAG_COMPLETE_FRAMES) {
> > +        next = buf_size;
> > +    } else {
> > +        int ret, flush = !buf_size;
> > +        next = find_frame_end(ctx, buf, buf_size);
> > +        if (ff_combine_frame(pc, next, &buf, &buf_size) < 0)
> > +            goto no_out;
> > +        ret = combine_au(ctx, avctx, &buf, &buf_size);
> > +        if (ret > 0 && flush) {
> > +            buf_size = 0;
> > +            ret = combine_au(ctx, avctx, &buf, &buf_size);
> > +        }
> > +        if (ret != 0) {
> > +            buf_size = next;
> > +            goto no_out;
> > +        }
> > +    }
> > +    *poutbuf      = buf;
> > +    *poutbuf_size = buf_size;
> > +    return next;
> > +no_out:
> > +    *poutbuf      = NULL;
> > +    *poutbuf_size = 0;
> > +    return buf_size;
> > +}
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