- https://developer.apple.com/videos/play/wwdc2019/506/ -- https://devstreaming-cdn.apple.com/videos/wwdc/2019/506lqy7sprpfyo800/506/506_hevc_video_with_alpha.pdf > Both Premultiplied Alpha and Straight Alpha are supported Single video track with ‘hvc1’ codec type • Two layers - Base layer: main profile; 4:2:0 video-range; nuh_layer_id 0 - Alpha layer: main profile; 4:2:0 full-range, neutral chroma channel; nuh_layer_id 1 • Base and alpha layers share one VPS - VPS extension required — indicates presence of alpha channel • Base and alpha layers have distinct PPS and SPS with different IDs • Base and alpha layers must have identical frame types and dependency structure • SEI alpha_channel_info message in hvcC in video format description - Indicates premultiplied alpha or straight alpha *. [#pabb735e] - 動画エフェクト負荷を大きく軽減した HEVCPlayerView 詳解 -- https://engineering.dena.com/blog/2022/07/hevcplayerview/
