Constant AV_VIDEO_ENC_PARAMS_VP9

pub const AV_VIDEO_ENC_PARAMS_VP9: i32 = 0;

VP9 stores:

• per-frame base (luma AC) quantizer index, exported as AVVideoEncParams.qp
• deltas for luma DC, chroma AC and chroma DC, exported in the corresponding entries in AVVideoEncParams.delta_qp
• per-segment delta, exported as for each block as AVVideoBlockParams.delta_qp

To compute the resulting quantizer index for a block:

• for luma AC, add the base qp and the per-block delta_qp, saturating to unsigned 8-bit.
• for luma DC and chroma AC/DC, add the corresponding AVVideoBlockParams.delta_qp to the luma AC index, again saturating to unsigned 8-bit.