Re: [FFmpeg-devel] [PATCH v2] cbs_av1: Make fake OBU size length field a write option

["Wang, Fei W" <fei.w.wang-at-intel.com@ffmpeg.org>]

On Tue, 2023-09-26 at 21:30 +0100, Mark Thompson wrote:
> This is an option to modify the behaviour of the writer, not a syntax
> field.
> ---
> On 26/09/2023 03:34, Wang, Fei W wrote:
> > On Mon, 2023-09-25 at 14:53 +0100, Mark Thompson wrote:
> > > ...
> > > diff --git a/libavcodec/vaapi_encode_av1.c
> > > b/libavcodec/vaapi_encode_av1.c
> > > index 3ff1c47b53..861bf4a13b 100644
> > > --- a/libavcodec/vaapi_encode_av1.c
> > > +++ b/libavcodec/vaapi_encode_av1.c
> > > @@ -133,6 +133,9 @@ static av_cold int
> > > vaapi_encode_av1_configure(AVCodecContext *avctx)
> > >        priv->cbc->trace_context = ctx;
> > >        priv->cbc->trace_write_callback =
> > > vaapi_encode_av1_trace_write_log;
> > > 
> > > +    av_opt_set_int(priv->cbc->priv_data,
> > > "fixed_obu_size_length",
> > > +                   priv->attr_ext2.bits.obu_size_bytes_minus1 +
> > > 1,
> > > 0);
> > > +
> > 
> > This should be put after querying priv.attr_ext2 in
> > vaapi_encode_av1_init().
> 
> Ah, true - I got my init and configure mixed up, but don't have
> convenient hardware to test.  Fixed in this version.

LGTM for this version.

Thanks
Fei

> 
> Thanks,
> 
> - Mark
> 
>   libavcodec/cbs_av1.c          | 31 +++++++++++++++++++++----------
>   libavcodec/cbs_av1.h          |  5 ++++-
>   libavcodec/vaapi_encode_av1.c |  4 +++-
>   3 files changed, 28 insertions(+), 12 deletions(-)
> 
> diff --git a/libavcodec/cbs_av1.c b/libavcodec/cbs_av1.c
> index 4e687ace79..ed9a7b80d4 100644
> --- a/libavcodec/cbs_av1.c
> +++ b/libavcodec/cbs_av1.c
> @@ -138,19 +138,25 @@ static int
> cbs_av1_read_leb128(CodedBitstreamContext *ctx, GetBitContext *gbc,
>       return 0;
>   }
> 
> -/** Minimum byte length will be used to indicate the len128 of value
> if byte_len is 0. */
>   static int cbs_av1_write_leb128(CodedBitstreamContext *ctx,
> PutBitContext *pbc,
> -                                const char *name, uint64_t value,
> uint8_t byte_len)
> +                                const char *name, uint64_t value,
> int fixed_length)
>   {
>       int len, i;
>       uint8_t byte;
> 
>       CBS_TRACE_WRITE_START();
> 
> -    if (byte_len)
> -        av_assert0(byte_len >= (av_log2(value) + 7) / 7);
> +    len = (av_log2(value) + 7) / 7;
> 
> -    len = byte_len ? byte_len : (av_log2(value) + 7) / 7;
> +    if (fixed_length) {
> +        if (fixed_length < len) {
> +            av_log(ctx->log_ctx, AV_LOG_ERROR, "OBU is too large for
> "
> +                   "fixed length size field (%d > %d).\n",
> +                   len, fixed_length);
> +            return AVERROR(EINVAL);
> +        }
> +        len = fixed_length;
> +    }
> 
>       for (i = 0; i < len; i++) {
>           if (put_bits_left(pbc) < 8)
> @@ -1006,8 +1012,8 @@ static int
> cbs_av1_write_obu(CodedBitstreamContext *ctx,
> 
>       if (obu->header.obu_has_size_field) {
>           pbc_tmp = *pbc;
> -        if (obu->obu_size_byte_len) {
> -            for (int i = 0; i < obu->obu_size_byte_len; i++)
> +        if (priv->fixed_obu_size_length) {
> +            for (int i = 0; i < priv->fixed_obu_size_length; i++)
>                   put_bits(pbc, 8, 0);
>           } else {
>               // Add space for the size field to fill later.
> @@ -1133,7 +1139,8 @@ static int
> cbs_av1_write_obu(CodedBitstreamContext *ctx,
>       end_pos   /= 8;
> 
>       *pbc = pbc_tmp;
> -    err = cbs_av1_write_leb128(ctx, pbc, "obu_size", obu->obu_size,
> obu->obu_size_byte_len);
> +    err = cbs_av1_write_leb128(ctx, pbc, "obu_size", obu->obu_size,
> +                               priv->fixed_obu_size_length);
>       if (err < 0)
>           goto error;
> 
> @@ -1150,10 +1157,12 @@ static int
> cbs_av1_write_obu(CodedBitstreamContext *ctx,
>       }
> 
>       if (obu->obu_size > 0) {
> -        if (!obu->obu_size_byte_len) {
> -            obu->obu_size_byte_len = start_pos - data_pos;
> +        if (!priv->fixed_obu_size_length) {
>               memmove(pbc->buf + data_pos,
>                       pbc->buf + start_pos, header_size);
> +        } else {
> +            // The size was fixed so the following data was
> +            // already written in the correct place.
>           }
>           skip_put_bytes(pbc, header_size);
> 
> @@ -1273,6 +1282,8 @@ static const CodedBitstreamUnitTypeDescriptor
> cbs_av1_unit_types[] = {
>   static const AVOption cbs_av1_options[] = {
>       { "operating_point",  "Set operating point to select layers to
> parse from a scalable bitstream",
>                             OFFSET(operating_point), AV_OPT_TYPE_INT,
> { .i64 = -1 }, -1, AV1_MAX_OPERATING_POINTS - 1, 0 },
> +    { "fixed_obu_size_length", "Set fixed length of the obu_size
> field",
> +      OFFSET(fixed_obu_size_length), AV_OPT_TYPE_INT, { .i64 = 0 },
> 0, 8, 0 },
>       { NULL }
>   };
> 
> diff --git a/libavcodec/cbs_av1.h b/libavcodec/cbs_av1.h
> index a9e2d2284f..7924257164 100644
> --- a/libavcodec/cbs_av1.h
> +++ b/libavcodec/cbs_av1.h
> @@ -401,7 +401,6 @@ typedef struct AV1RawOBU {
>       AV1RawOBUHeader header;
> 
>       size_t obu_size;
> -    uint8_t obu_size_byte_len;
> 
>       union {
>           AV1RawSequenceHeader sequence_header;
> @@ -468,6 +467,10 @@ typedef struct CodedBitstreamAV1Context {
> 
>       // AVOptions
>       int operating_point;
> +    // When writing, fix the length in bytes of the obu_size field.
> +    // Writing will fail with an error if an OBU larger than can be
> +    // represented by the fixed size is encountered.
> +    int fixed_obu_size_length;
>   } CodedBitstreamAV1Context;
> 
> 
> diff --git a/libavcodec/vaapi_encode_av1.c
> b/libavcodec/vaapi_encode_av1.c
> index 3ff1c47b53..5a9ff0f798 100644
> --- a/libavcodec/vaapi_encode_av1.c
> +++ b/libavcodec/vaapi_encode_av1.c
> @@ -634,7 +634,6 @@ static int
> vaapi_encode_av1_init_picture_params(AVCodecContext *avctx,
>           }
>       }
> 
> -    fh_obu->obu_size_byte_len = priv-
> >attr_ext2.bits.obu_size_bytes_minus1 + 1;
>       ret = vaapi_encode_av1_add_obu(avctx, obu,
> AV1_OBU_FRAME_HEADER, &priv->fh);
>       if (ret < 0)
>           goto end;
> @@ -839,6 +838,9 @@ static av_cold int
> vaapi_encode_av1_init(AVCodecContext *avctx)
>           priv->attr_ext2.value = attr.value;
>       }
> 
> +    av_opt_set_int(priv->cbc->priv_data, "fixed_obu_size_length",
> +                   priv->attr_ext2.bits.obu_size_bytes_minus1 + 1,
> 0);
> +
>       ret = vaapi_encode_av1_set_tile(avctx);
>       if (ret < 0)
>           return ret;
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