ffmpeg入门之 Tutorial01 分类： ffmpeg-SDL-VLC-Live555 2013-08-22 17:54 495人阅读评论(0) 收藏

#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 %d %d 255 ", 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;
static int sws_flags = SWS_BICUBIC;
struct SwsContext *img_convert_ctx;
AVPicture pict;
argc = 2;
argv[1] = "d:\temp\test.264";
if(argc < 2) {
    printf("Please provide a movie file ");
    return -1;
}
// /*注册所有可用的格式和编解码器*/
av_register_all();

// Open video file /*以输入方式打开一个媒体文件,也即源文件,
codecs并没有打开,只读取了文件的头信息*/
if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0)
    return -1; // Couldn't open file

// Retrieve stream information
/*通过读取媒体文件的中的包来获取媒体文件中的流信息,对于没有头信息的文件如(mpeg)是非常有用的,

// 该函数通常重算类似mpeg-2帧模式的真实帧率,该函数并未改变逻辑文件的position.
*/
if(av_find_stream_info(pFormatCtx)<0)
return -1; // Couldn't find stream information

// Dump information about file onto standard error
//该函数的作用就是检查下初始化过程中设置的参数是否符合规范

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 < 0)
{
      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);
/*通过code ID查找一个已经注册的音视频编码器,查找编码器之前,必须先调用av_register_all注册所有支持的编码器
音视频编码器保存在一个链表中,查找过程中,函数从头到尾遍历链表,通过比较编码器的ID来查找

*/
if(pCodec==NULL) {
fprintf(stderr, "Unsupported codec! ");
return -1; // Codec not found
}
// Open codec
//使用给定的AVCodec初始化AVCodecContext

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

    #if 0
     // Convert the image into YUV format that SDL uses
     img_convert(&pict, PIX_FMT_YUV420P,
         (AVPicture *)pFrame, pCodecCtx->pix_fmt,
       pCodecCtx->width, pCodecCtx->height);
    #else
      /*   img_convert(&pict, dst_pix_fmt,
      (AVPicture *)pFrame, is->video_st->codec->pix_fmt,
      is->video_st->codec->width, is->video_st->codec->height);
      */

        img_convert_ctx = sws_getContext( pCodecCtx->width,
               pCodecCtx->height,
               pCodecCtx->pix_fmt,
               pCodecCtx->width,
               pCodecCtx->height,
               PIX_FMT_YUV420P,
               sws_flags, NULL, NULL, NULL);

        sws_scale(img_convert_ctx,(const uint8_t* const*)pFrame->data,pFrame->linesize,0,pCodecCtx->height,pFrameRGB->data,pFrameRGB->linesize);
        sws_freeContext(img_convert_ctx);
    #endif

     // Save the frame to disk
     if((++i<=100)&&(i>95))
       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;
}

ffmpeg入门之 Tutorial01 分类： ffmpeg-SDL-VLC-Live555 2013-08-22 17:54 495人阅读 评论(0) 收藏

ffmpeg入门之 Tutorial01 分类： ffmpeg-SDL-VLC-Live555 2013-08-22 17:54 495人阅读评论(0) 收藏