Android 音視頻深入 十二 FFmpeg視頻替換聲音（附源碼下載）

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項目地址，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

一個視頻有三個流，視頻流，音頻流，字幕流，我將視頻A的視頻流拿出來，將音樂B的音頻流拿出來，合在一起成新的視頻

還是老規矩直接說c代碼如何運行

註冊組件，開啟並獲得MP4檔案和MP3檔案的資訊

av_register_all();//Inputif ((ret = avformat_open_input(&ifmt_ctx_v, in_filename_v, 0, 0)) < 0) {//開啟輸入的視頻檔案    LOGE( "Could not open input file.");    goto end;}if ((ret = avformat_find_stream_info(ifmt_ctx_v, 0)) < 0) {//擷取視頻檔案資訊    LOGE( "Failed to retrieve input stream information");    goto end;}if ((ret = avformat_open_input(&ifmt_ctx_a, in_filename_a, 0, 0)) < 0) {//開啟輸入的音頻檔案    LOGE( "Could not open input file.");    goto end;}if ((ret = avformat_find_stream_info(ifmt_ctx_a, 0)) < 0) {//擷取音頻檔案資訊    LOGE( "Failed to retrieve input stream information");    goto end;}

建立輸出檔案

 //Outputavformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);//初始化輸出碼流的AVFormatContext。if (!ofmt_ctx) {    LOGE( "Could not create output context\n");    ret = AVERROR_UNKNOWN;    return -1;}ofmt = ofmt_ctx->oformat;

擷取MP4的視頻流和MP3的音頻流

//從輸入的AVStream中擷取一個輸出的out_streamfor (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);//建立流通道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;    }}

擷取輸出檔案的資訊並開啟輸出檔案，獲得輸出資料流

LOGE("==========Output Information==========\n");av_dump_format(ofmt_ctx, 0, out_filename, 1);LOGE("======================================\n");//Open output fileif (!(ofmt->flags & AVFMT_NOFILE)) {    if (avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE) < 0) {//開啟輸出檔案。        LOGE( "Could not open output file ‘%s‘", out_filename);        return -1;    }}//Write file headerif (avformat_write_header(ofmt_ctx, NULL) < 0) {    LOGE( "Error occurred when opening output file\n");    return -1;}

接下來就是邊解碼邊編碼了，這個解碼是解碼視頻流和音頻流，這個兩個流解碼速度需要保持一致
這個通過雙方時間軸來判斷，然後就將解碼的資料編碼放入輸出檔案

    //Get an AVPacket .   av_compare_ts是比較時間戳記用的。通過該函數可以決定該寫入視頻還是音頻。    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)

開始是先解碼視頻，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裸流沒有PTS，因此必須手動寫入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);        }

接著是解碼音頻放入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;        }

然後就是將之前解碼的資料編碼放入輸出檔案，釋放這個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 音頻或視頻裸流    if (av_interleaved_write_frame(ofmt_ctx, &pkt) < 0) {        LOGE( "Error muxing packet\n");        break;    }

av_free_packet(&pkt);

通過不斷地迴圈，解碼一下視頻流，解碼一下音頻流，編碼放入輸出檔案，這三個步驟不斷迴圈完成合成視頻

完成輸出視頻，並釋放資源

//Write file trailerav_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;}

下一次依舊與音頻有關係

Android 音視頻深入 十二 FFmpeg視頻替換聲音（附源碼下載）