[FFmpeg-devel] [PATCH] lavc/vaapi_encode_h265: add low_delay_b option for HEVC

[mypopy at gmail.com]

On Mon, Apr 13, 2020 at 12:39 PM Linjie Fu <linjie.fu at intel.com> wrote:
>
> Low delay B-frame is supported on ICL+ platform.
>
> For low power encoding, low_delay_b should be enabled by default.
>
> Low delay B:
> <http://what-when-how.com/Tutorial/topic-397pct9eq3/High-Efficiency-Video-Coding-HEVC-288.html>
>
> There is an on-going work in libva and media-driver to add querys
> support for low delay b, would add it once it's ready:
> https://github.com/intel/libva/pull/220
> https://github.com/intel/libva/pull/364
> https://github.com/intel/media-driver/issues/721
>
> Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> ---
>  doc/encoders.texi              |  8 ++++++++
>  libavcodec/vaapi_encode_h265.c | 19 +++++++++++++++++--
>  2 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/doc/encoders.texi b/doc/encoders.texi
> index e23b6b3..b0812be 100644
> --- a/doc/encoders.texi
> +++ b/doc/encoders.texi
> @@ -3089,6 +3089,14 @@ Some combination of the following values:
>  Include HDR metadata if the input frames have it
>  (@emph{mastering_display_colour_volume} and @emph{content_light_level}
>  messages).
> +
> + at item low_delay_b
> +Use low delay B-frames instead of P frames. Reordering of pictures is
> +not allowed. The first picture is encoded as an I picture and subsequent
> +pictures are encoded as B pictures. Moreover, since past B pictures are
> +used for prediction, a low coding delay but with higher coding efficiency
> +(because of bi-prediction) is achieved.
> +
>  @end table
>
>  @end table
> diff --git a/libavcodec/vaapi_encode_h265.c b/libavcodec/vaapi_encode_h265.c
> index 97dc5a7..cd48545 100644
> --- a/libavcodec/vaapi_encode_h265.c
> +++ b/libavcodec/vaapi_encode_h265.c
> @@ -62,6 +62,7 @@ typedef struct VAAPIEncodeH265Context {
>      int tier;
>      int level;
>      int sei;
> +    int low_delay_b;
>
>      // Derived settings.
>      int fixed_qp_idr;
> @@ -894,6 +895,9 @@ static int vaapi_encode_h265_init_slice_params(AVCodecContext *avctx,
>
>      sh->slice_type = hpic->slice_type;
>
> +    if (sh->slice_type == HEVC_SLICE_P && priv->low_delay_b)
> +        sh->slice_type = HEVC_SLICE_B;
Add a trace or info message in this, it's will help to reduce the
sudden surprises, the other question is, if enable the  low_delay_b in
 ICL-  platform, what is the result of this?

> +
>      sh->slice_pic_order_cnt_lsb = hpic->pic_order_cnt &
>          (1 << (sps->log2_max_pic_order_cnt_lsb_minus4 + 4)) - 1;
>
> @@ -1054,9 +1058,13 @@ static int vaapi_encode_h265_init_slice_params(AVCodecContext *avctx,
>          vslice->ref_pic_list0[0] = vpic->reference_frames[0];
>      }
>      if (pic->nb_refs >= 2) {
> -        // Forward reference for B-frame.
>          av_assert0(pic->type == PICTURE_TYPE_B);
> -        vslice->ref_pic_list1[0] = vpic->reference_frames[1];
> +        if (priv->low_delay_b)
> +            // Reference for low delay B-frame
> +            vslice->ref_pic_list1[0] = vpic->reference_frames[0];
> +        else
> +            // Forward reference for B-frame.
> +            vslice->ref_pic_list1[0] = vpic->reference_frames[1];
>      }
>
>      return 0;
> @@ -1181,6 +1189,11 @@ static av_cold int vaapi_encode_h265_init(AVCodecContext *avctx)
>      if (priv->qp > 0)
>          ctx->explicit_qp = priv->qp;
>
> +    /* low_delay_b is required for low power encoding */
> +    priv->low_delay_b = ctx->low_power ? 1 : priv->low_delay_b;
> +    if (priv->low_delay_b)
> +        av_log(avctx, AV_LOG_VERBOSE, "Low delay B-frame enabled.\n");
> +
>      return ff_vaapi_encode_init(avctx);
>  }
>
> @@ -1256,6 +1269,8 @@ static const AVOption vaapi_encode_h265_options[] = {
>        0, AV_OPT_TYPE_CONST,
>        { .i64 = SEI_MASTERING_DISPLAY | SEI_CONTENT_LIGHT_LEVEL },
>        INT_MIN, INT_MAX, FLAGS, "sei" },
> +    { "low_delay_b", "Use low delay B frames instead of P frames",
> +      OFFSET(low_delay_b), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, FLAGS },
>
>      { NULL },
>  };
> --
> 2.7.4
>
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-- 
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Jun zhao/赵军
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