Method createCodecContext

src/video_encoder.ts:142–228

(config: VideoEncoderConfig)

	}

	private static createCodecContext(config: VideoEncoderConfig) {
		const inferred = inferCodecFromCodecString(config.codec);
		if (!inferred) {
			throw new Error('Unsupported codec');
		}

		if (config.alpha === 'keep') {
			throw new DOMException('Alpha encoding is not supported.', 'NotSupportedError');
		}

		if (config.bitrateMode === 'quantizer') {
			throw new DOMException('Quantizer bitrate mode is not supported.', 'NotSupportedError');
		}

		let codec: Codec | null = null;
		if (!canUseHwAccel() || config.hardwareAcceleration === 'prefer-software') {
			codec = Codec.findEncoder(inferred);
		} else {
			codec = getHardwareEncoderCodec(inferred) ?? Codec.findEncoder(inferred);
		}

		if (!codec) {
			return null;
		}

		const codecContext = new CodecContext();
		codecContext.allocContext3(codec);

		let pixelFormat = AV_PIX_FMT_YUV420P;
		if (codec.pixelFormats && !codec.pixelFormats.includes(AV_PIX_FMT_YUV420P)) {
			pixelFormat = codec.pixelFormats[0];
		}

		codecContext.width = config.width;
		codecContext.height = config.height;
		codecContext.pixelFormat = pixelFormat;
		codecContext.timeBase = new Rational(1, 1e6);
		codecContext.gopSize = 60;
		codecContext.framerate = new Rational(Math.round(config.framerate ?? 0) || 30, 1);
		codecContext.bitRate = BigInt(config.bitrate ?? getDecentVideoBitrate(inferred, config.width, config.height));

		if (config.bitrateMode === 'constant') {
			codecContext.rcMinRate = codecContext.bitRate;
			codecContext.rcMaxRate = codecContext.bitRate;
		}

		const isRealtime = config.latencyMode === 'realtime';

		if (codec.name === 'libx264') {
			if (isRealtime) {
				codecContext.setOption('tune', 'zerolatency');
				codecContext.setOption('preset', 'ultrafast');
			}
		} else if (codec.name === 'libx265') {
			codecContext.setOption('x265-params', 'log-level=error');

			if (isRealtime) {
				codecContext.setOption('tune', 'zerolatency');