使用FFmpeg+GDI解码和播放视频

矫情吗；* 2022-07-15 03:25 321阅读 0赞

[完整源码][Link 1]

[FFmpeg][]是跨平台的流媒体处理解决方案，包括了libavformat和libavcodec等库用来解码流媒体

本篇文章使用FFmpeg 3.1.5解码视频，现有的教程比较老了，avcodec\_decode\_video2等API已经不用了，用avcodec\_send\_packet和avcodec\_receive\_frame代替

API参考文档： [FFmpeg Documentation][]

使用FFmpeg前去官网下载dev版和shared版，在项目中导入dev版的头文件和lib库，然后把shared版中的dll放到你的程序目录下

使用FFmpeg解码视频步骤：

1.  程序开始时用av\_register\_all注册解码器
2.  用avformat\_open\_input打开视频文件，用avformat\_find\_stream\_info获取流信息
3.  找到要解码的流的索引（这里用了第一个视频流）
4.  用avcodec\_find\_decoder找到解码器，用avcodec\_open2初始化
5.  为了得到RGB数据用sws\_getContext注册颜色转换器
6.  用av\_read\_frame从流中读取packet
7.  用avcodec\_send\_packet和avcodec\_receive\_frame解码packet，再用sws\_scale转换颜色格式到RGB

Decoder.h：

#pragma once
    extern "C"
    {
    #include <libavformat/avformat.h>
    #include <libavcodec/avcodec.h>
    #include <libswscale/swscale.h>
    };
    #include <thread>
    #include <memory>
    #include <functional>
    
    
    class CDecoder
    {
    public:
    	CDecoder(LPCSTR fileName);
    	virtual ~CDecoder();
    
    	virtual void Run();
    	virtual void Pause();
    	virtual void Stop();
    
    	virtual void GetVideoSize(SIZE& size);
    
    	// 设置需要呈现时的回调函数
    	virtual void SetOnPresent(std::function<void(BYTE*)>&& onPresent);
    
    protected:
    	AVFormatContext* m_formatCtx = NULL;
    	int m_videoStreamIndex = -1;
    	AVCodecContext* m_codecCtx = NULL;
    	AVCodec* m_codec = NULL;
    	SwsContext* m_swsCtx = NULL;
    
    	enum DecodeState{ DECODE_RUN, DECODE_PAUSE, DECODE_STOP };
    	DecodeState m_decodeState = DECODE_STOP;
    	std::unique_ptr<std::thread> m_decodeThread;
    	std::unique_ptr<BYTE[]> m_imgData;
    
    	SIZE m_videoSize;
    	// 需要呈现时被调用
    	std::function<void(BYTE*)> m_onPresent;
    
    	void DecodeThread();
    };

Decoder.cpp：

#include "stdafx.h"
    #include "Decoder.h"
    
    
    CDecoder::CDecoder(LPCSTR fileName)
    {
    	int ret;
    
    	// 容器
    	ret = avformat_open_input(&m_formatCtx, fileName, NULL, NULL);
    	ret = avformat_find_stream_info(m_formatCtx, NULL);
    	for (UINT i = 0; i < m_formatCtx->nb_streams; i++)
    	{
    		if (m_formatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
    		{
    			m_videoStreamIndex = i;
    			break;
    		}
    	}
    
    	// 解码器
    	AVCodecParameters* codecpar = m_formatCtx->streams[m_videoStreamIndex]->codecpar;
    	m_codec = avcodec_find_decoder(codecpar->codec_id);
    	m_codecCtx = avcodec_alloc_context3(m_codec);
    	ret = avcodec_open2(m_codecCtx, m_codec, NULL);
    
    	m_videoSize.cx = codecpar->width;
    	m_videoSize.cy = codecpar->height;
    
    	// 颜色转换器
    	m_swsCtx = sws_getContext(m_videoSize.cx, m_videoSize.cy, (AVPixelFormat)codecpar->format, m_videoSize.cx,
    		m_videoSize.cy, AV_PIX_FMT_BGRA, SWS_BICUBIC, NULL, NULL, NULL);
    
    	m_imgData.reset(new BYTE[m_videoSize.cx * m_videoSize.cy * 4]);
    }
    
    CDecoder::~CDecoder()
    {
    	// 停止解码线程
    	m_decodeState = DECODE_STOP;
    	if (m_decodeThread != nullptr)
    		m_decodeThread->join();
    
    	sws_freeContext(m_swsCtx);
    	avcodec_free_context(&m_codecCtx);
    	avformat_close_input(&m_formatCtx);
    }
    
    void CDecoder::Run()
    {
    	TRACE(_T("Run\n"));
    	if (m_decodeState == DECODE_RUN)
    		return;
    
    	// 启动解码线程
    	if (m_decodeThread != nullptr)
    		m_decodeThread->join();
    	m_decodeState = DECODE_RUN;
    	m_decodeThread.reset(new std::thread(&CDecoder::DecodeThread, this));
    }
    
    void CDecoder::Pause()
    {
    	TRACE(_T("Pause\n"));
    	if (m_decodeState != DECODE_RUN)
    		return;
    
    	// 停止解码线程
    	m_decodeState = DECODE_PAUSE;
    	if (m_decodeThread != nullptr)
    	{
    		m_decodeThread->join();
    		m_decodeThread = nullptr;
    	}
    }
    
    void CDecoder::Stop()
    {
    	TRACE(_T("Stop\n"));
    	if (m_decodeState == DECODE_STOP)
    		return;
    
    	// 停止解码线程
    	m_decodeState = DECODE_STOP;
    	if (m_decodeThread != nullptr)
    	{
    		m_decodeThread->join();
    		m_decodeThread = nullptr;
    	}
    
    	av_seek_frame(m_formatCtx, m_videoStreamIndex, 0, 0);
    }
    
    void CDecoder::GetVideoSize(SIZE& size)
    {
    	size = m_videoSize;
    }
    
    void CDecoder::SetOnPresent(std::function<void(BYTE*)>&& onPresent)
    {
    	m_onPresent = std::move(onPresent);
    }
    
    void CDecoder::DecodeThread()
    {
    	AVFrame *frame = av_frame_alloc();
    	AVPacket packet;
    
    	while (m_decodeState == DECODE_RUN && av_read_frame(m_formatCtx, &packet) >= 0)
    	{
    		if (packet.stream_index != m_videoStreamIndex)
    			continue;
    
    		// 解码
    		avcodec_send_packet(m_codecCtx, &packet);
    		if (avcodec_receive_frame(m_codecCtx, frame) != 0)
    			continue;
    
    		// 转换颜色格式
    		BYTE* pImgData = m_imgData.get();
    		int stride = m_codecCtx->width * 4;
    		sws_scale(m_swsCtx, frame->data, frame->linesize, 0, m_codecCtx->height, &pImgData, &stride);
    
    		// 呈现
    		if (!m_onPresent._Empty())
    			m_onPresent(m_imgData.get());
    
    		// 粗略的视频同步
    		Sleep(DWORD(((float)m_codecCtx->time_base.num / (float)m_codecCtx->time_base.den) * 1000));
    	}
    	if (m_decodeState == DECODE_RUN)
    		m_decodeState = DECODE_STOP;
    
    	av_packet_unref(&packet);
    	av_frame_free(&frame);
    	TRACE(_T("DecodeThread结束\n"));
    }

使用方法：

m_decoder = new CDecoder("E:\\pump it.avi");
    	m_decoder->SetOnPresent(std::bind(&CFFmpegGDIDlg::OnPresent, this, std::placeholders::_1));
    
    	m_decoder->GetVideoSize(m_videoSize);
    	m_dc.Create(m_videoSize.cx, m_videoSize.cy, 32);
    
    	m_decoder->Run();
    
    // ......
    
    void CFFmpegGDIDlg::OnPresent(BYTE* data)
    {
    	m_dcLock.Lock();
    	// RGB位图都是从下到上储存的，data不是
    	for (int y = 0; y < m_videoSize.cy; y++)
    	{
    		memcpy(m_dc.GetPixelAddress(0, y), data, m_videoSize.cx * 4);
    		data += m_videoSize.cx * 4;
    	}
    	m_dcLock.Unlock();
    
    	Invalidate(FALSE);
    }

这里我只是粗略的同步视频，视频播放速度可能比实际慢，比较精确的方法参考这篇文章： [Tutorial 05: Synching Video][Tutorial 05_ Synching Video]

[Link 1]: https://github.com/xfgryujk/DecodeVideo/tree/master/FFmpegGDI
[FFmpeg]: https://ffmpeg.org/
[FFmpeg Documentation]: https://ffmpeg.org/doxygen/trunk/index.html
[Tutorial 05_ Synching Video]: http://dranger.com/ffmpeg/tutorial05.html