On Mon, 2023-09-25 at 14:53 +0100, Mark Thompson wrote:
> This is an option to modify the behaviour of the writer, not a syntax
> field.
> ---
> Tested by hacking av1_metadata. For example, adding:
>
> av_opt_set_int(ctx->common.output->priv_data,
> "fixed_obu_size_length", 7, 0);
>
> gets you OBU headers that look like:
>
> [trace_headers @ 0x55706fcb2880] OBU header
> [trace_headers @ 0x55706fcb2880]
> 0 obu_forbidden_bit
> 0 = 0
> [trace_headers @ 0x55706fcb2880]
> 1 obu_type
> 0100 = 4
> [trace_headers @ 0x55706fcb2880]
> 5 obu_extension_flag
> 0 = 0
> [trace_headers @ 0x55706fcb2880]
> 6 obu_has_size_field
> 1 = 1
> [trace_headers @ 0x55706fcb2880]
> 7 obu_reserved_1bit
> 0 = 0
> [trace_headers @ 0x55706fcb2880]
> 8 obu_size 10101110100010101000000010000000100000001000000
> 000000000 = 1326
>
> It's not obvious that there is any value in exposing this option more
> generally, though? It could made a visible option of av1_metadata or
> others if there is any use-case for it.
>
> 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..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().
Thanks
Fei
> if (ctx->rc_mode->quality) {
> priv->q_idx_p = av_clip(ctx->rc_quality, 0, AV1_MAX_QUANT);
> if (fabs(avctx->i_quant_factor) > 0.0)
> @@ -634,7 +637,6 @@ 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;
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