Android 音视频深入 十二 FFmpeg视频替换声音（附源码下载）

项目地址，求star
https://github.com/979451341/AudioVideoStudyCodeTwo/tree/master/FFmpeg%E7%BB%99%E8%A7%86%E9%A2%91%E6%8D%A2%E5%A3%B0%E9%9F%B3

一个视频有三个流，视频流，音频流，字幕流，我将视频A的视频流拿出来，将音乐B的音频流拿出来，合在一起成新的视频

还是老规矩直接说c代码如何运行

注册组件，打开并获得MP4文件和MP3文件的信息

av_register_all();
//Input
if ((ret = avformat_open_input(&ifmt_ctx_v, in_filename_v, 0, 0)) < 0) {//打开输入的视频文件
    LOGE( "Could not open input file.");
    goto end;
}
if ((ret = avformat_find_stream_info(ifmt_ctx_v, 0)) < 0) {//获取视频文件信息
    LOGE( "Failed to retrieve input stream information");
    goto end;
}

if ((ret = avformat_open_input(&ifmt_ctx_a, in_filename_a, 0, 0)) < 0) {//打开输入的音频文件
    LOGE( "Could not open input file.");
    goto end;
}
if ((ret = avformat_find_stream_info(ifmt_ctx_a, 0)) < 0) {//获取音频文件信息
    LOGE( "Failed to retrieve input stream information");
    goto end;
}

创建输出文件

 //Output
avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);//初始化输出码流的AVFormatContext。
if (!ofmt_ctx) {
    LOGE( "Could not create output context\n");
    ret = AVERROR_UNKNOWN;
    return -1;
}
ofmt = ofmt_ctx->oformat;

获取MP4的视频流和MP3的音频流

//从输入的AVStream中获取一个输出的out_stream
for (i = 0; i < ifmt_ctx_v->nb_streams; i++) {
    //Create output AVStream according to input AVStream
    if(ifmt_ctx_v->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
        AVStream *in_stream = ifmt_ctx_v->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);//创建流通道AVStream
        videoindex_v=i;
        if (!out_stream) {
            LOGE( "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            break;
        }
        videoindex_out=out_stream->index;
        //Copy the settings of AVCodecContext
        if (avcodec_copy_context(out_stream->codec, in_stream->codec) < 0) {
            LOGE( "Failed to copy context from input to output stream codec context\n");
            break;
        }
        out_stream->codec->codec_tag = 0;
        if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
            out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
        break;
    }
}

for (i = 0; i < ifmt_ctx_a->nb_streams; i++) {
    //Create output AVStream according to input AVStream
    if(ifmt_ctx_a->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO){
        AVStream *in_stream = ifmt_ctx_a->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
        audioindex_a=i;
        if (!out_stream) {
            LOGE( "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }
        audioindex_out=out_stream->index;
        //Copy the settings of AVCodecContext
        if (avcodec_copy_context(out_stream->codec, in_stream->codec) < 0) {
            LOGE( "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;

        break;
    }
}

获取输出文件的信息并打开输出文件，获得输出流

LOGE("==========Output Information==========\n");
av_dump_format(ofmt_ctx, 0, out_filename, 1);
LOGE("======================================\n");
//Open output file
if (!(ofmt->flags & AVFMT_NOFILE)) {
    if (avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE) < 0) {//打开输出文件。
        LOGE( "Could not open output file '%s'", out_filename);
        return -1;
    }
}
//Write file header
if (avformat_write_header(ofmt_ctx, NULL) < 0) {
    LOGE( "Error occurred when opening output file\n");
    return -1;
}

接下来就是边解码边编码了，这个解码是解码视频流和音频流，这个两个流解码速度需要保持一致
这个通过双方时间轴来判断，然后就将解码的数据编码放入输出文件

    //Get an AVPacket .   av_compare_ts是比较时间戳用的。通过该函数可以决定该写入视频还是音频。
    if(av_compare_ts(cur_pts_v,ifmt_ctx_v->streams[videoindex_v]->time_base,cur_pts_a,ifmt_ctx_a->streams[audioindex_a]->time_base) <= 0)

开始是先解码视频，放入cur_pts_v

        if(av_read_frame(ifmt_ctx, &pkt) >= 0){
            do{
                in_stream  = ifmt_ctx->streams[pkt.stream_index];
                out_stream = ofmt_ctx->streams[stream_index];

                if(pkt.stream_index==videoindex_v){
                    //FIX：No PTS (Example: Raw H.264) H.264裸流没有PTS，因此必须手动写入PTS
                    //Simple Write PTS
                    if(pkt.pts==AV_NOPTS_VALUE){
                        //Write PTS
                        AVRational time_base1=in_stream->time_base;
                        //Duration between 2 frames (us)
                        int64_t calc_duration=(double)AV_TIME_BASE/av_q2d(in_stream->r_frame_rate);
                        //Parameters
                        pkt.pts=(double)(frame_index*calc_duration)/(double)(av_q2d(time_base1)*AV_TIME_BASE);
                        pkt.dts=pkt.pts;
                        pkt.duration=(double)calc_duration/(double)(av_q2d(time_base1)*AV_TIME_BASE);
                        frame_index++;
                    }

                    cur_pts_v=pkt.pts;
                    break;
                }
            }while(av_read_frame(ifmt_ctx, &pkt) >= 0);
        }

接着是解码音频放入cur_pts_a

        if(av_read_frame(ifmt_ctx, &pkt) >= 0){
            do{
                in_stream  = ifmt_ctx->streams[pkt.stream_index];
                out_stream = ofmt_ctx->streams[stream_index];

                if(pkt.stream_index==audioindex_a){

                    //FIX：No PTS
                    //Simple Write PTS
                    if(pkt.pts==AV_NOPTS_VALUE){
                        //Write PTS
                        AVRational time_base1=in_stream->time_base;
                        //Duration between 2 frames (us)
                        int64_t calc_duration=(double)AV_TIME_BASE/av_q2d(in_stream->r_frame_rate);
                        //Parameters
                        pkt.pts=(double)(frame_index*calc_duration)/(double)(av_q2d(time_base1)*AV_TIME_BASE);
                        pkt.dts=pkt.pts;
                        pkt.duration=(double)calc_duration/(double)(av_q2d(time_base1)*AV_TIME_BASE);
                        frame_index++;
                    }
                    cur_pts_a=pkt.pts;

                    break;
                }
            }while(av_read_frame(ifmt_ctx, &pkt) >= 0);
        }else{
            break;
        }

然后就是将之前解码的数据编码放入输出文件，释放这个pkt

    //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;
    pkt.stream_index=stream_index;
    LOGE("Write 1 Packet. size:%5d\tpts:%lld\n",pkt.size,pkt.pts);
    //Write AVPacket 音频或视频裸流
    if (av_interleaved_write_frame(ofmt_ctx, &pkt) < 0) {
        LOGE( "Error muxing packet\n");
        break;
    }

av_free_packet(&pkt);

通过不断地循环，解码一下视频流，解码一下音频流，编码放入输出文件，这三个步骤不断循环完成合成视频

完成输出视频，并释放资源

//Write file trailer
av_write_trailer(ofmt_ctx);

#if USE_H264BSF
av_bitstream_filter_close(h364bsfc);
#endif
#if USE_AACBSF
av_bitstream_filter_close(aacbsfc);
#endif

end:
avformat_close_input(&ifmt_ctx_v);
avformat_close_input(&ifmt_ctx_a);
/* 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) {
    LOGE( "Error occurred.\n");
    return -1;
}

下一次依旧与音频有关系