void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) { FILE *pFile; char szFilename[32]; int y; // Open file sprintf(szFilename, "frame%d.ppm", iFrame); pFile=fopen(szFilename, "wb"); if(pFile==NULL) return; // Write header fprintf(pFile, "P6\n%d %d\n255\n", width, height); // Write pixel data for(y=0; y fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile); // Close file fclose(pFile); }
int main(int argc, char *argv[]) { AVFormatContext *pFormatCtx; int i, videoStream; AVCodecContext *pCodecCtx; AVCodec *pCodec; AVFrame *pFrame; AVFrame *pFrameRGB; AVPacket packet; int frameFinished; int numBytes; uint8_t *buffer; if(argc < 2) { printf("Please provide a movie file\n"); return -1; } // Register all formats and codecs ######################################## [1] ######################################## av_register_all(); // Open video file ######################################## [2] ######################################## if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0) return -1; // Couldn't open file // Retrieve stream information ######################################## [3] ######################################## if(av_find_stream_info(pFormatCtx)<0) return -1; // Couldn't find stream information // Dump information about file onto standard error dump_format(pFormatCtx, 0, argv[1], 0); // Find the first video stream videoStream=-1; for(i=0; inb_streams; i++) if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO) { videoStream=i; break; } if(videoStream==-1) return -1; // Didn't find a video stream // Get a pointer to the codec context for the video stream pCodecCtx=pFormatCtx->streams[videoStream]->codec; // Find the decoder for the video stream pCodec=avcodec_find_decoder(pCodecCtx->codec_id); if(pCodec==NULL) { fprintf(stderr, "Unsupported codec!\n"); return -1; // Codec not found } // Open codec if(avcodec_open(pCodecCtx, pCodec)<0) return -1; // Could not open codec // Allocate video frame pFrame=avcodec_alloc_frame(); // Allocate an AVFrame structure pFrameRGB=avcodec_alloc_frame(); if(pFrameRGB==NULL) return -1; // Determine required buffer size and allocate buffer numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t)); // Assign appropriate parts of buffer to image planes in pFrameRGB // Note that pFrameRGB is an AVFrame, but AVFrame is a superset // of AVPicture avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); // Read frames and save first five frames to disk ######################################## [4] ######################################## i=0; while(av_read_frame(pFormatCtx, &packet)>=0) { // Is this a packet from the video stream? if(packet.stream_index==videoStream) { // Decode video frame avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, packet.data, packet.size); // Did we get a video frame? if(frameFinished) { // Convert the image from its native format to RGB img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24, (AVPicture*)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height); // Save the frame to disk if(++i<=5) SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i); } } // Free the packet that was allocated by av_read_frame av_free_packet(&packet); } // Free the RGB image av_free(buffer); av_free(pFrameRGB); // Free the YUV frame av_free(pFrame); // Close the codec avcodec_close(pCodecCtx); // Close the video file av_close_input_file(pFormatCtx); return 0; }
[2]:先说说里面的AVFormatContext *pFormatCtx结构，字面意思理解AVFormatContext 就是关于AVFormat(其实就是我们上面说的Container格式)的所处的Context(场景)，自 然是保存Container信息的总控结构了，后面你也可以看到，基本上所有的信息，都可 以从它出发而获取到 我们来看看av_open_input_file()都做了些什么： [libavformat/utils.c] int av_open_input_file(AVFormatContext **ic_ptr, const char *filename, AVInputFormat *fmt, int buf_size, AVFormatParameters *ap) { ...... if (!fmt) { /* guess format if no file can be opened */ fmt = av_probe_input_format(pd, 0); }
