学步园

参考http://m.oschina.net/blog/56616调通了ffmpeg例程

gcc test_decode_frames.c  -I/usr/local/include -lavcodec -lavformat -lswscale -lavutil

#include <stdlib.h>
#include <stdio.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>

static void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame)
{
    FILE *pFile;
    char szFilename[32];
    int y;

    sprintf(szFilename, "frame%d.ppm", iFrame);
    pFile = fopen(szFilename, "wb");
    if (!pFile)
        return;
    fprintf(pFile, "P6\n%d %d\n255\n", width, height);

    for (y = 0; y < height; y++)
        fwrite(pFrame->data[0] + y * pFrame->linesize[0], 1, width * 3, pFile);

    fclose(pFile);
}


int main(int argc, char* argv[])
{
    AVFormatContext *pFormatCtx = NULL;
    int             i           = 0;
    int             videoStream = 0;
    AVCodecContext  *pCodecCtx  = 0;
    AVCodec         *pCodec     = NULL;
    AVFrame         *pFrame     = 0;
    AVFrame         *pFrameRGB  = NULL;
    AVPacket        packet;
    int             gotPic      = 0;
    int             bytesUsed   = 0;
    int             numBytes    = 0;
    uint8_t         *buffer     = NULL;

    // 注册所有 muxer/demuxer, encoder/decoder
    av_register_all();

    // 打开一个文件, 读文件头
    if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0)
        return -1;

    // 获取文件中的流信息
    if (avformat_find_stream_info(pFormatCtx, NULL ) < 0)
        return -1;

    // 输出文件信息到终端
    av_dump_format(pFormatCtx, -1, argv[1], 0);

    // 找到第一个视频流
    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;

    // 打开解码器
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL)
        return -1;
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
        return -1;

    // 申请帧缓存
    pFrame = avcodec_alloc_frame();
    if (pFrame == NULL)
        return -1;
    pFrameRGB = avcodec_alloc_frame();
    if (pFrameRGB == NULL)
        return -1;

    numBytes = avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
                                  pCodecCtx->height);
    buffer = av_malloc(numBytes);
    avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
                   pCodecCtx->width, pCodecCtx->height);

    // 读取帧数据==>解码==>色彩空间转换==>保存PPM文件
    i = 0;
    while (av_read_frame(pFormatCtx, &packet) >= 0)
    {
        if (packet.stream_index == videoStream)
        {
            gotPic = 0;
            bytesUsed = 0;
            bytesUsed = avcodec_decode_video2(pCodecCtx, pFrame, &gotPic, &packet);

            if (gotPic &&  (bytesUsed > 0))
            {
                struct SwsContext *img_convert_ctx = NULL;
                img_convert_ctx = sws_getCachedContext(img_convert_ctx, pCodecCtx->width,
                                                       pCodecCtx->height, pCodecCtx->pix_fmt,
                                                       pCodecCtx->width, pCodecCtx->height,
                                                       PIX_FMT_RGB24, SWS_BICUBIC,
                                                       NULL, NULL, NULL);
                if (!img_convert_ctx)
                {
                    fprintf(stderr, "Cannot initialize sws conversion context\n");
                    exit(1);
                }
                sws_scale(img_convert_ctx, (const uint8_t * const*)pFrame->data,
                          pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data,
                          pFrameRGB->linesize);
                if (i++ < 50)
                    SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);
            }
        }
    }

    av_free(buffer);
    av_free(pFrameRGB);
    av_free(pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;

}