【音视频】视频转码-SWS（二）

继桌面采集之后的第二篇关于音视频的文章，本篇主要实现视频的转码，将采集的BRGA转码为YUV420。

技术简介

使用ffmpeg sws实现转码。

使用模块（库）

ffmpeg的swscale-5.dll

主要流程和代码

1、初始化转码器，srcFmt是AV_PIX_FMT_BGRA，dstFmt是AV_PIX_FMT_YUV420P

int FfmpegSwsTranscoder::init(AVPixelFormat srcFmt, int srcWidth, int srcHeight, AVPixelFormat dstFmt, int dstWidth, int dstHeight)
{
	int err = ERROR_CODE_OK;
	if (m_inited) {
		return err;
	}

	m_swsContext = sws_getContext(srcWidth, srcHeight, srcFmt, dstWidth, dstHeight, dstFmt, 
		SWS_BICUBIC, nullptr, nullptr, nullptr);
	if (m_swsContext == nullptr) {
		err = ERROR_CODE_FFMPEG_GET_SWS_CONTEXT_FAILED;
		return err;
	}

	m_bufferSize = av_image_get_buffer_size(dstFmt, dstWidth, dstHeight, 1);
	m_buffer = (uint8_t*)av_malloc(m_bufferSize);
	if (m_buffer == nullptr) {
		err = ERROR_CODE_ALLOC_FAILED;
		return err;
	}

	m_frame = av_frame_alloc();
	if (m_frame == nullptr) {
		err = ERROR_CODE_FFMPEG_ALLOC_FRAME_FAILED;
		return err;
	}

	int ret = av_image_fill_arrays(m_frame->data, m_frame->linesize, m_buffer, dstFmt, dstWidth, dstHeight, 1);
	if (ret < 0) {
		err = ERROR_CODE_FFMPEG_FILL_IMAGE_FAILED;
		return err;
	}

	m_inited = true;

	return err;
}

2、转码

int FfmpegSwsTranscoder::transcode(const AVFrame* srcFrame, AVFrame** dstFrame, uint8_t** dstData, uint32_t* dstLen)
{
	int err = ERROR_CODE_OK;

	if (!m_inited || m_swsContext == nullptr) {
		err = ERROR_CODE_UNINITIALIZED;
		return err;
	}

	int ret = sws_scale(m_swsContext, srcFrame->data, srcFrame->linesize, 0, srcFrame->height, 
		m_frame->data, m_frame->linesize);
	if (ret <= 0) {
		err = ERROR_CODE_FFMPEG_SWS_SCALE_FAILED;
		return err;
	}

	m_frame->format = srcFrame->format;
	m_frame->width = srcFrame->width;
	m_frame->height = srcFrame->height;
	m_frame->pict_type = srcFrame->pict_type;
	m_frame->pts = srcFrame->pts;
	m_frame->pkt_dts = srcFrame->pkt_dts;

	*dstFrame = m_frame;
	*dstData = m_buffer;
	*dstLen = m_bufferSize;

	return err;
}

至此，就可以拿到视频帧数据进行下一步操作了，那就是编码。

PS：视频转码是音视频技术中使用起来相对简单的一个了。