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(h264bsfc);
#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