ffmpeg使用例程

// avcodec_sample.cpp // A small sample program that shows how to use libavformat and libavcodec to // read video from a file. // // Use // // g++ -o avcodec_sample avcodec_sample.cpp -lavformat -lavcodec -lz // // to build (assuming libavformat and libavcodec are correctly installed on // your system). // // Run using // // avcodec_sample myvideofile.mpg // // to write the first five frames from “myvideofile.mpg” to disk in PPM // format. #include <avcodec.h> #include <avformat.h> #include <stdio.h> bool GetNextFrame(AVFormatContext *pFormatCtx, AVCodecContext *pCodecCtx, int videoStream, AVFrame *pFrame) { static AVPacket packet; static int bytesRemaining=0; static uint8_t *rawData; static bool fFirstTime=true; int bytesDecoded; int frameFinished; // First time were called, set packet.data to NULL to indicate it // doesnt have to be freed if(fFirstTime) { fFirstTime=false; packet.data=NULL; } // Decode packets until we have decoded a complete frame while(true) { // Work on the current packet until we have decoded all of it while(bytesRemaining > 0) { // Decode the next chunk of data bytesDecoded=avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, rawData, bytesRemaining); // Was there an error? if(bytesDecoded < 0) { fprintf(stderr, “Error while decoding frame\n”); return false; } bytesRemaining-=bytesDecoded; rawData+=bytesDecoded; // Did we finish the current frame? Then we can return if(frameFinished) return true; } // Read the next packet, skipping all packets that arent for this // stream do { // Free old packet if(packet.data!=NULL) av_free_packet(&packet); // Read new packet if(av_read_packet(pFormatCtx, &packet)<0) goto loop_exit; } while(packet.stream_index!=videoStream); bytesRemaining=packet.size; rawData=packet.data; } loop_exit: // Decode the rest of the last frame bytesDecoded=avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, rawData, bytesRemaining); // Free last packet if(packet.data!=NULL) av_free_packet(&packet); return frameFinished!=0; } 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<height; 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; int numBytes; uint8_t *buffer; // Register all formats and codecs av_register_all(); // Open video file if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0) return -1; // Couldnt open file // Retrieve stream information if(av_find_stream_info(pFormatCtx)<0) return -1; // Couldnt find stream information // Dump information about file onto standard error dump_format(pFormatCtx, 0, argv[1], false); // Find the first video stream videoStream=-1; for(i=0; i<pFormatCtx->nb_streams; i++) if(pFormatCtx->streams[i]->codec.codec_type==CODEC_TYPE_VIDEO) { videoStream=i; break; } if(videoStream==-1) return -1; // Didnt 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) return -1; // Codec not found // Inform the codec that we can handle truncated bitstreams — i.e., // bitstreams where frame boundaries can fall in the middle of packets if(pCodec->capabilities & CODEC_CAP_TRUNCATED) pCodecCtx->flags|=CODEC_FLAG_TRUNCATED; // Open codec if(avcodec_open(pCodecCtx, pCodec)<0) return -1; // Could not open codec // Hack to correct wrong frame rates that seem to be generated by some // codecs if(pCodecCtx->frame_rate>1000 && pCodecCtx->frame_rate_base==1) pCodecCtx->frame_rate_base=1000; // 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=new uint8_t[numBytes]; // Assign appropriate parts of buffer to image planes in pFrameRGB avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); // Read frames and save first five frames to disk i=0; while(GetNextFrame(pFormatCtx, pCodecCtx, videoStream, pFrame)) { 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 RGB image delete [] 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; }