H264 Tutorial

tutorial01.c

// tutorial01.c//// This tutorial was written by Stephen Dranger ([e-mail]).//// Code based on a tutorial by Martin Bohme ([e-mail])// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1// A small sample program that shows how to use libavformat and libavcodec to// read video from a file.//// Use the Makefile to build all examples.//// Run using//// tutorial01 myvideofile.mpg//// to write the first five frames from "myvideofile.mpg" to disk in PPM// format.#include <libavcodec/avcodec.h>#include <libavformat/avformat.h>#include <libswscale/swscale.h>#include <stdio.h>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 = NULL;  int             i, videoStream;  AVCodecContext  *pCodecCtx = NULL;  AVCodec         *pCodec = NULL;  AVFrame         *pFrame = NULL;   AVFrame         *pFrameRGB = NULL;  AVPacket        packet;  int             frameFinished;  int             numBytes;  uint8_t         *buffer = NULL;  AVDictionary    *optionsDict = NULL;  struct SwsContext      *sws_ctx = NULL;  if(argc < 2) {    printf("Please provide a movie file\n");    return -1;  }  // Register all formats and codecs  av_register_all();  // Open video file  if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL)!=0)    return -1; // Couldn't open file  // Retrieve stream information  if(avformat_find_stream_info(pFormatCtx, NULL)<0)    return -1; // Couldn't find stream information  // Dump information about file onto standard error  av_dump_format(pFormatCtx, 0, argv[1], 0);  // Find the first video stream  videoStream=-1;  for(i=0; i<pFormatCtx->nb_streams; i++)    if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_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_open2(pCodecCtx, pCodec, &optionsDict)<0)    return -1; // Could not open codec  // Allocate video frame  pFrame=av_frame_alloc();  // Allocate an AVFrame structure  pFrameRGB=av_frame_alloc();  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));  sws_ctx =    sws_getContext    (        pCodecCtx->width,        pCodecCtx->height,        pCodecCtx->pix_fmt,        pCodecCtx->width,        pCodecCtx->height,        PIX_FMT_RGB24,        SWS_BILINEAR,        NULL,        NULL,        NULL    );  // 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  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_video2(pCodecCtx, pFrame, &frameFinished,                &packet);      // Did we get a video frame?      if(frameFinished) {    // Convert the image from its native format to RGB        sws_scale        (            sws_ctx,            (uint8_t const * const *)pFrame->data,            pFrame->linesize,            0,            pCodecCtx->height,            pFrameRGB->data,            pFrameRGB->linesize        );    // 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  avformat_close_input(&pFormatCtx);  return 0;}