下面贴上代码，代码是从FFmpeg的例子改编的，平台是VC2010。

/*
 *最简单的基于FFmpeg的封装格式转换器
 *Simplest FFmpeg Remuxer
 *
 *雷霄骅 Lei Xiaohua
 *leixiaohua1020@126.com
 *中国传媒大学/数字电视技术
 *Communication University of China / Digital TV Technology
 *http://blog.csdn.net/leixiaohua1020
 *
 *本程序实现了视频封装格式之间的转换。
 *需要注意的是本程序并不改变视音频的编码格式。
 *
 * This software converts a media file from one container format
 * to another container format without encoding/decoding video files.
 */
 
#include "stdafx.h"
 
extern "C"
{
#include "libavformat/avformat.h"
};
 
 
int _tmain(int argc, _TCHAR* argv[])
{
    AVOutputFormat *ofmt = NULL;
    //输入对应一个AVFormatContext，输出对应一个AVFormatContext
    //（Input AVFormatContext and Output AVFormatContext）
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    const char *in_filename, *out_filename;
    int ret, i;
    if (argc < 3) {
        printf("usage: %s input output\n"
            "Remux a media file with libavformat and libavcodec.\n"
            "The output format is guessed according to the file extension.\n"
            "Modified by Lei Xiaohua, leixiaohua1020@126.com\n"
            "Communication University of China / Digital TV Technology\n"
            "http://blog.csdn.net/leixiaohua1020", argv[0]);
        return 1;
    }
    in_filename  = argv[1];//输入文件名（Input file URL）
    out_filename = argv[2];//输出文件名（Output file URL）
    av_register_all();
    //输入（Input）
    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
        printf( "Could not open input file.");
        goto end;
    }
    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        printf( "Failed to retrieve input stream information");
        goto end;
    }
    av_dump_format(ifmt_ctx, 0, in_filename, 0);
    //输出（Output）
    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        printf( "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }
    ofmt = ofmt_ctx->oformat;
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        //根据输入流创建输出流（Create output AVStream according to input AVStream）
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
        if (!out_stream) {
            printf( "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }
        //复制AVCodecContext的设置（Copy the settings of AVCodecContext）
        ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
        if (ret < 0) {
            printf( "Failed to copy context from input to output stream codec context\n");
            goto end;
        }
        out_stream->codec->codec_tag = 0;
        if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
            out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
    }
    //输出一下格式------------------
    av_dump_format(ofmt_ctx, 0, out_filename, 1);
    //打开输出文件（Open output file）
    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            printf( "Could not open output file ‘%s‘", out_filename);
            goto end;
        }
    }
    //写文件头（Write file header）
    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        printf( "Error occurred when opening output file\n");
        goto end;
    }
    int frame_index=0;
    while (1) {
        AVStream *in_stream, *out_stream;
        //获取一个AVPacket（Get an AVPacket）
        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;
        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];
        /* copy packet */
        //转换PTS/DTS（Convert PTS/DTS）
        pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
        pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
        pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
        //写入（Write）
        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            printf( "Error muxing packet\n");
            break;
        }
        printf("Write %8d frames to output file\n",frame_index);
        av_free_packet(&pkt);
        frame_index++;
    }
    //写文件尾（Write file trailer）
    av_write_trailer(ofmt_ctx);
end:
    avformat_close_input(&ifmt_ctx);
    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_close(ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);
    if (ret < 0 && ret != AVERROR_EOF) {
        printf( "Error occurred.\n");
        return -1;
    }
    return 0;
}

 

完整工程下载地址：

http://download.csdn.net/detail/leixiaohua1020/7323491