tutorial01.c

ffmpeg开发指南

// tutorial01.c
// 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
//
// gcc -o tutorial01 tutorial01.c -lavutil -lavformat -lavcodec -lz
//
// to build (assuming libavformat and libavcodec are correctly installed
// your system).
//
// Run using
//
// tutorial01 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>

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;
  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
  av_register_all();
  
  // Open video file
  if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0)
    return -1; // Couldn't open file
  
  // Retrieve stream information
  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; i<pFormatCtx->nb_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
  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;
}