2023-03-14：读取摄像头，并且显示视频。代码用go语言编写。

答案2023-03-14：

大体流程如下：

导入所需的库和包。

初始化 ffmpeg 和 SDL2 库。

打开摄像头并创建 AVFormatContext ​​结构体。

查找视频流，并且打开视频解码器。

创建 SDL 窗口，用于显示视频。

创建 AVFrame 结构体，用于存储解码后的视频帧数据。

创建 AVPacket 结构体，用于存储编码后的视频数据。

创建 SwsContext 结构体，用于转换视频帧格式。

不断从视频流读取 AVPacket，直到读完所有帧。

解码 AVPacket 中的视频数据，将其存储在 AVFrame 中。

将 AVFrame 中的数据转换为适合 SDL 窗口显示的格式。

显示转换后的图像帧。

释放所有资源，包括关闭 SDL 窗口、释放 AVFrame 和 AVPacket、删除 SwsContext 结构体、关闭解码器、关闭视频流、关闭摄像头。

需要注意的是，在实际使用中可能会遇到各种问题，例如视频格式不支持、分辨率不匹配等。因此，我们需要根据具体情况来进行相应的调整和处理，以确保程序能够正常运行。

这段代码调用了以下结构体：

AVFormatContext：表示 FFmpeg 格式上下文，包含视频文件的信息和元数据。

AVCodecContext：表示视频编解码器上下文，用于配置和控制编解码器。

AVPacket：表示一个压缩的音频或视频数据包，包含了一帧或多帧音频或视频数据。

AVFrame：表示一个解码后的视频帧，存储原始像素数据以及相关的元数据。

SwsContext：表示视频帧转换器上下文，用于将解码后的视频帧从一种格式转换为另一种格式。

SDL_Window：表示 SDL 窗口，用于显示视频图像。

SDL_Renderer：表示 SDL 渲染器，用于将视频帧渲染到 SDL 窗口中。

这些结构体是实现视频播放所必需的重要组件。它们之间的交互、设置和使用都可以影响视频播放的效果和性能，因此需要仔细地处理和配置。同时，在释放资源时，需要确保所有相关的结构体被正确销毁，以避免内存泄漏和其他问题。

代码见github.com/moonfdd/ffmpeg-go-examples。

执行命令：

go run ./examples/leixiaohua1020/simplest_ffmpeg_readcamera/main.go

代码参考了雷霄骅的本地摄像头数据的获取解码和显示，代码用golang编写。代码如下：

// https://github.com/leixiaohua1020/simplest_ffmpeg_device/blob/master/simplest_ffmpeg_readcamera/simplest_ffmpeg_readcamera.cpp
package mainimport ("fmt""os""time""unsafe""github.com/moonfdd/ffmpeg-go/ffcommon""github.com/moonfdd/ffmpeg-go/libavcodec""github.com/moonfdd/ffmpeg-go/libavdevice""github.com/moonfdd/ffmpeg-go/libavformat""github.com/moonfdd/ffmpeg-go/libavutil""github.com/moonfdd/ffmpeg-go/libswscale"sdl "github.com/moonfdd/sdl2-go/sdl2""github.com/moonfdd/sdl2-go/sdlcommon"
)// Output YUV420P
const OUTPUT_YUV420P = 0// '1' Use Dshow
// '0' Use GDIgrab
const USE_DSHOW = 0// Refresh Event
const SFM_REFRESH_EVENT = (sdl.SDL_USEREVENT + 1)
const SFM_BREAK_EVENT = (sdl.SDL_USEREVENT + 2)var thread_exit ffcommon.FInt = 0
var ispush = truefunc sfp_refresh_thread(opaque ffcommon.FVoidP) uintptr {// thread_exit = 0for thread_exit == 0 {var event sdl.SDL_Eventevent.Type = SFM_REFRESH_EVENTif ispush {event.SDL_PushEvent()ispush = false}sdl.SDL_Delay(40)}fmt.Println("sfp_refresh_thread 发送退出事件")// thread_exit = 0//Breakvar event sdl.SDL_Eventevent.Type = SFM_BREAK_EVENTevent.SDL_PushEvent()return 0
}// Show Dshow Device
func show_dshow_device() {pFormatCtx := libavformat.AvformatAllocContext()var options *libavutil.AVDictionarylibavutil.AvDictSet(&options, "list_devices", "true", 0)iformat := libavformat.AvFindInputFormat("dshow")fmt.Printf("========Device Info=============\n")libavformat.AvformatOpenInput(&pFormatCtx, "video=dummy", iformat, &options)fmt.Printf("================================\n")
}// Show AVFoundation Device
func show_avfoundation_device() {pFormatCtx := libavformat.AvformatAllocContext()var options *libavutil.AVDictionarylibavutil.AvDictSet(&options, "list_devices", "true", 0)iformat := libavformat.AvFindInputFormat("avfoundation")fmt.Printf("==AVFoundation Device Info===\n")libavformat.AvformatOpenInput(&pFormatCtx, "", iformat, &options)fmt.Printf("=============================\n")
}func main0() (ret ffcommon.FInt) {var pFormatCtx *libavformat.AVFormatContextvar i, videoindex ffcommon.FIntvar pCodecCtx *libavcodec.AVCodecContextvar pCodec *libavcodec.AVCodecvar ifmt *libavformat.AVInputFormatlibavformat.AvRegisterAll()libavformat.AvformatNetworkInit()pFormatCtx = libavformat.AvformatAllocContext()//Open File//char filepath[]="src01_480x272_22.h265";//avformat_open_input(&pFormatCtx,filepath,NULL,NULL)//Register Devicelibavdevice.AvdeviceRegisterAll()/解码器部分////打开摄像头ifmt = libavformat.AvFindInputFormat("dshow")var options *libavutil.AVDictionary// libavutil.AvDictSet(&options, "probesize", "100000000", 0)// libavutil.AvDictSet(&options, "rtbufsize", "100000000", 0)if libavformat.AvformatOpenInput(&pFormatCtx, "video=Full HD webcam", ifmt, &options) < 0 {fmt.Printf("Cannot open camera.\n")return}if pFormatCtx.AvformatFindStreamInfo(nil) < 0 {fmt.Println("Couldn't find stream information.")return -1}videoindex = -1for i = 0; i < int32(pFormatCtx.NbStreams); i++ {if pFormatCtx.GetStream(uint32(i)).Codec.CodecType == libavutil.AVMEDIA_TYPE_VIDEO {videoindex = ibreak}}if videoindex == -1 {fmt.Printf("Didn't find a video stream.\n")return -1}pCodecCtxPara := pFormatCtx.GetStream(uint32(videoindex)).CodecparpCodec = libavcodec.AvcodecFindDecoder(pCodecCtxPara.CodecId)if pCodec == nil {fmt.Printf("Codec not found.\n")return -1}pCodecCtx = pCodec.AvcodecAllocContext3()if pCodecCtx == nil {fmt.Printf("Cannot alloc valid decode codec context.\n")return}if pCodecCtx.AvcodecParametersToContext(pCodecCtxPara) < 0 {fmt.Printf("Cannot initialize parameters.\n")return}if pCodecCtx.AvcodecOpen2(pCodec, nil) < 0 {fmt.Printf("Could not open codec.\n")return -1}var pFrame, pFrameYUV *libavutil.AVFramepFrame = libavutil.AvFrameAlloc()pFrameYUV = libavutil.AvFrameAlloc()//unsigned char *out_buffer=(unsigned char *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));//avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);out_buffer := (*byte)(unsafe.Pointer(libavutil.AvMalloc(uint64(libavcodec.AvpictureGetSize(int32(libavutil.AV_PIX_FMT_YUV420P), pCodecCtx.Width, pCodecCtx.Height)))))((*libavcodec.AVPicture)(unsafe.Pointer(pFrameYUV))).AvpictureFill(out_buffer, libavutil.AV_PIX_FMT_YUV420P, pCodecCtx.Width, pCodecCtx.Height)//SDL----------------------------// if sdl.SDL_Init(sdl.SDL_INIT_VIDEO|sdl.SDL_INIT_AUDIO|sdl.SDL_INIT_TIMER) != 0 {if sdl.SDL_Init(sdl.SDL_INIT_VIDEO) != 0 {fmt.Printf("Could not initialize SDL - %s\n", sdl.SDL_GetError())return -1}var screen_w, screen_h ffcommon.FInt = 640, 360// var mode *sdl.SDL_DisplayMode = new(sdl.SDL_DisplayMode)// if sdl.SDL_GetCurrentDisplayMode(0, mode) != 0 {// 	fmt.Printf("SDL: could not get current display mode - exiting:%s\n", sdl.SDL_GetError())// 	return -1// }//Half of the Desktop's width and height.screen_w = pCodecCtx.Widthscreen_h = pCodecCtx.Heightwindow := sdl.SDL_CreateWindow("Simplest FFmpeg Read Camera", sdl.SDL_WINDOWPOS_UNDEFINED, sdl.SDL_WINDOWPOS_UNDEFINED, screen_w, screen_h, 0)if window == nil {fmt.Printf("SDL: could not create window - exiting:%s\n", sdl.SDL_GetError())return -1}window.SDL_ShowWindow()time.Sleep(2 * time.Second)defer window.SDL_DestroyWindow()renderer := window.SDL_CreateRenderer(-1, 0)if renderer == nil {fmt.Printf("SDL: could not create renderer - exiting:%s\n", sdl.SDL_GetError())return -1}defer renderer.SDL_DestroyRenderer()texture := renderer.SDL_CreateTexture(sdl.SDL_PIXELFORMAT_YV12,sdl.SDL_TEXTUREACCESS_STREAMING,pCodecCtx.Width,pCodecCtx.Height)defer texture.SDL_DestroyTexture()var rect sdl.SDL_Rectrect.X = 0rect.Y = 0rect.W = screen_wrect.H = screen_hvar rect2 sdl.SDL_Rectrect2.X = 0rect2.Y = 0rect2.W = pCodecCtx.Widthrect2.H = pCodecCtx.Height//SDL End------------------------// var got_picture ffcommon.FInt//AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket));packet := &libavcodec.AVPacket{}var fp_yuv *os.Fileif OUTPUT_YUV420P != 0 {fp_yuv, _ = os.Create("output.yuv")}var img_convert_ctx *libswscale.SwsContextimg_convert_ctx = libswscale.SwsGetContext(pCodecCtx.Width, pCodecCtx.Height, pCodecCtx.PixFmt, pCodecCtx.Width, pCodecCtx.Height, libavutil.AV_PIX_FMT_YUV420P, libswscale.SWS_BICUBIC, nil, nil, nil)//------------------------------//video_tid := sdl.SDL_CreateThread(sfp_refresh_thread, nil)//go sfp_refresh_thread(uintptr(0))//sdl.SDL_CreateThread(sfp_refresh_thread, "", uintptr(0))//Event Loopvar event sdl.SDL_Eventfor {//Waitispush = trueevent.SDL_WaitEvent()if event.Type == SFM_REFRESH_EVENT {//------------------------------if pFormatCtx.AvReadFrame(packet) >= 0 {if int32(packet.StreamIndex) == videoindex {if pCodecCtx.AvcodecSendPacket(packet) < 0 {packet.AvPacketUnref()continue}ret = pCodecCtx.AvcodecReceiveFrame(pFrame)if ret < 0 {fmt.Printf("Decode Error.\n")return -1}if ret >= 0 {// if got_picture != 0 {img_convert_ctx.SwsScale((**byte)(unsafe.Pointer(&pFrame.Data)), (*int32)(unsafe.Pointer(&pFrame.Linesize)), 0, uint32(pCodecCtx.Height), (**byte)(unsafe.Pointer(&pFrameYUV.Data)), (*int32)(unsafe.Pointer(&pFrameYUV.Linesize)))if OUTPUT_YUV420P != 0 {y_size := pCodecCtx.Width * pCodecCtx.Heightfp_yuv.Write(ffcommon.ByteSliceFromByteP(pFrameYUV.Data[0], int(y_size)))   //Yfp_yuv.Write(ffcommon.ByteSliceFromByteP(pFrameYUV.Data[1], int(y_size)/4)) //Ufp_yuv.Write(ffcommon.ByteSliceFromByteP(pFrameYUV.Data[2], int(y_size)/4)) //V}texture.SDL_UpdateYUVTexture(&rect2,pFrameYUV.Data[0], pFrameYUV.Linesize[0],pFrameYUV.Data[1], pFrameYUV.Linesize[1],pFrameYUV.Data[2], pFrameYUV.Linesize[2])renderer.SDL_RenderClear()renderer.SDL_RenderCopy(texture, nil, &rect)renderer.SDL_RenderPresent()}}packet.AvFreePacket()} else {//Exit Threadthread_exit = 1fmt.Println("main 准备退出 1")}} else if event.Type == sdl.SDL_QUIT {thread_exit = 1fmt.Println("main 准备退出 2")} else if event.Type == SFM_BREAK_EVENT {fmt.Println("退出循环 3")break}}img_convert_ctx.SwsFreeContext()if OUTPUT_YUV420P != 0 {fp_yuv.Close()}sdl.SDL_Quit()libavutil.AvFree(uintptr(unsafe.Pointer(out_buffer)))libavutil.AvFree(uintptr(unsafe.Pointer(pFrame)))libavutil.AvFree(uintptr(unsafe.Pointer(pFrameYUV)))pCodecCtx.AvcodecClose()libavformat.AvformatCloseInput(&pFormatCtx)return 0
}func main() {os.Setenv("Path", os.Getenv("Path")+";./lib/windows/ffmpeg")ffcommon.SetAvutilPath("./lib/windows/ffmpeg/avutil-56.dll")ffcommon.SetAvcodecPath("./lib/windows/ffmpeg/avcodec-58.dll")ffcommon.SetAvdevicePath("./lib/windows/ffmpeg/avdevice-58.dll")ffcommon.SetAvfilterPath("./lib/windows/ffmpeg/avfilter-56.dll")ffcommon.SetAvformatPath("./lib/windows/ffmpeg/avformat-58.dll")ffcommon.SetAvpostprocPath("./lib/windows/ffmpeg/postproc-55.dll")ffcommon.SetAvswresamplePath("./lib/windows/ffmpeg/swresample-3.dll")ffcommon.SetAvswscalePath("./lib/windows/ffmpeg/swscale-5.dll")sdlcommon.SetSDL2Path("./lib/windows/sdl/SDL2.0.16.dll")genDir := "./out"_, err := os.Stat(genDir)if err != nil {if os.IsNotExist(err) {os.Mkdir(genDir, 0777) //  Everyone can read write and execute}}// go func() {// 	time.Sleep(1000)// 	exec.Command("./lib/ffplay.exe", "rtmp://localhost/publishlive/livestream").Output()// 	if err != nil {// 		fmt.Println("play err = ", err)// 	}// }()main0()
}