基于FFMPEG的音频编码器

悠悠 2022-06-17 12:06 368阅读 0赞

## 编码模块 ##

借鉴雷霄骅的PCM编码为AAC。  
url: [http://blog.csdn.net/leixiaohua1020/article/details/25430449][http_blog.csdn.net_leixiaohua1020_article_details_25430449]

编码模块是编码存放在FIFO中的数据，然后udp输出，具体的数据流向图如下：  
![这里写图片描述][SouthEast]  
编码模块数据流向图  
编码前，为32位双声道48KHz的PCM数据，因为ffmpeg MP2编码器所支持的PCM数据为16位，所以需要PCM重采样。  
   
编码单独为一个线程，具体的程序流程图如下。图中蓝色背景为实际输出数据函数，浅绿色为编码函数，棕色为PCM重采样函数。  
![这里写图片描述][SouthEast 1]  
![这里写图片描述][SouthEast 2]

简单介绍下流程中各函数意义：  
av\_register\_all()：注册FFmpeg所有编解码器。  
avformat\_ network\_init()：注册FFmpeg所有网络协议。（如果没有，不能udp、rtmp等输出）  
avformat\_alloc\_output\_context2()：初始化输出码流的AVFormatContext。  
avio\_open()：打开输出文件。  
av\_new\_stream()：创建输出码流的AVStream。  
avcodec\_find\_encoder()：查找编码器。  
avcodec\_open2()：打开编码器。  
avformat\_write\_header()：写文件头（对于某些没有文件头的封装格式，不需要此函数。比如说MPEG2TS）。  
swr\_convert ()：PCM重采样。即将frame\_buf的原始数据PCM重采样后，写到AVFrame.data中去。  
avcodec\_encode\_audio2()：编码音频。即将AVFrame（存储PCM采样数据）编码为AVPacket（存储AAC，MP3等格式的码流数据）。  
av\_write\_frame()：将编码后的视频码流写入文件。  
av\_write\_trailer()：写文件尾（对于某些没有文件头的封装格式，不需要此函数。比如说MPEG2TS）。

代码实现如下：

struct SwrContext *swr_config_coder(struct SwrContext *s)
    {
        if(NULL == s)
        {
            s = swr_alloc();
        }
        s = swr_alloc_set_opts(s,         // we're allocating a new context
                AV_CH_LAYOUT_STEREO,    // out_ch_layout
                AV_SAMPLE_FMT_S16,      // out_sample_fmt
                SWR_SAMPLE_RATE,        // out_sample_rate
                AV_CH_LAYOUT_STEREO,    // in_ch_layout
                AV_SAMPLE_FMT_S32,      // in_sample_fmt
                SWR_SAMPLE_RATE,        // in_sample_rate
                0,                      // log_offset
                NULL);                  // log_ctx
        swr_init(s);
    
        return s;
    }
    
    
    int flush_encoder(AVFormatContext *fmt_ctx,unsigned int stream_index)
    {
        int ret;
        int got_frame;
        AVPacket enc_pkt;
        if (!(fmt_ctx->streams[stream_index]->codec->codec->capabilities &
            CODEC_CAP_DELAY))
            return 0;
        while (1)
        {
            enc_pkt.data = NULL;
            enc_pkt.size = 0;
            av_init_packet(&enc_pkt);
            ret = avcodec_encode_audio2 (fmt_ctx->streams[stream_index]->codec, &enc_pkt,
                NULL, &got_frame);
            av_frame_free(NULL);
            if (ret < 0)
                break;
            if (!got_frame){
                ret=0;
                break;
            }
            printf("Flush Encoder: Succeed to encode 1 frame!\tsize:%5d\n",enc_pkt.size);
            /* mux encoded frame */
            ret = av_write_frame(fmt_ctx, &enc_pkt);
            if (ret < 0)
                break;
        }
        return ret;
    }
    
    void * Coder_Thread(void * arg)
    {
        UDP_Lock();
        //define use struct
        AVFormatContext* pFormatCtx = NULL;
        AVOutputFormat* fmt = NULL;
        AVStream* audio_st = NULL;
        AVCodecContext* pCodecCtx = NULL;
        AVCodec* pCodec = NULL;
        SwrContext* swr_ctx = NULL;                 //pcm转换结构体
    
        uint8_t* frame_buf[SWR_CH_MAX];
        AVPacket pkt;
        AVFrame* pFrame = NULL;
    
        int got_frame=0;
        int dst_nb_samples;
        int ret=0;
        int size=0;
    
        //int64_t now_time = 0;
        //int64_t last_time = 0;
    
    #ifdef DEBUG_CODER_FIFO
        int pipe_fd;
        int open_mode = O_RDONLY;
    
        if (access(CODER_FIFO_NAME, F_OK) == -1)
        {
            ret = mkfifo(CODER_FIFO_NAME, 0777);
            if (ret != 0)
            {
                DEBUG_LOG("Could not create fifo %s\n", CODER_FIFO_NAME);
            }
        }
    
        pipe_fd = open(CODER_FIFO_NAME, open_mode);
        if(pipe_fd == -1)
        {
            DEBUG_LOG("Cannot open FIFO");
            return NULL;
        }
    #endif
    
        char out_file[32];
        ST_PEBROCASTOUTPUT stPE_BrocastOutput;
        PARAMS_GetBroadCastOutput(&stPE_BrocastOutput);
        snprintf(out_file, 32, "udp://%d.%d.%d.%d:%d",
                stPE_BrocastOutput.u8BroadCastIpAddr[0],
                stPE_BrocastOutput.u8BroadCastIpAddr[1],
                stPE_BrocastOutput.u8BroadCastIpAddr[2],
                stPE_BrocastOutput.u8BroadCastIpAddr[3],
                stPE_BrocastOutput.u8BroadCasDesttPort);
        DEBUG_LOG("udp_url : %s", out_file);
    
    #ifdef DEBUG_CODER_PCM
        //fixme tset swrpcmout
        FILE *pout_file = NULL;
        int data_size;
        pout_file = fopen("S16.pcm", "wb");
    #endif
    
        //ser config
        swr_ctx = swr_config_coder(swr_ctx);
        if(swr_ctx == NULL)
        {
            DEBUG_LOG("swr_ctx config fail!");
            return NULL;
        }
    
        av_register_all();
        avformat_network_init();
    
        //Method 1.
        //pFormatCtx = avformat_alloc_context();
        //fmt = av_guess_format(NULL, out_file, NULL);
        //pFormatCtx->oformat = fmt;
    
    
        //Method 2.
        avformat_alloc_output_context2(&pFormatCtx, NULL, "mpegts", out_file);
        if(!pFormatCtx)
        {
            DEBUG_LOG("Could not create output context\n");
            return NULL ;
        }
        fmt = pFormatCtx->oformat;
    
        //Open output URL
        if (avio_open(&pFormatCtx->pb, out_file, AVIO_FLAG_WRITE) < 0)
        {
            DEBUG_LOG("Failed to open output file!\n");
            return NULL;
        }
    
        audio_st = avformat_new_stream(pFormatCtx, NULL);
        if (audio_st == NULL)
        {
            return NULL ;
        }
    
        //set codec param
        pCodecCtx = audio_st->codec;
        pCodecCtx->codec_id = fmt->audio_codec;
        pCodecCtx->codec_type = AVMEDIA_TYPE_AUDIO;
        pCodecCtx->sample_fmt = AV_SAMPLE_FMT_S16;
        pCodecCtx->sample_rate= 48000;
        pCodecCtx->channel_layout = AV_CH_LAYOUT_STEREO;
        pCodecCtx->channels = av_get_channel_layout_nb_channels(pCodecCtx->channel_layout);
        //fixme
        //pCodecCtx->bit_rate = 64000;
    
        //Show some information
        //av_dump_format(pFormatCtx, 0, out_file, 1);
    
        //open encoder
        pCodec = avcodec_find_encoder(pCodecCtx->codec_id);
        if (!pCodec){
            DEBUG_LOG("Can not find encoder!\n");
            return NULL ;
        }
        if (avcodec_open2(pCodecCtx, pCodec,NULL) < 0){
            DEBUG_LOG("Failed to open encoder!\n");
            return NULL ;
        }
    
        //new frame
        pFrame = av_frame_alloc();
        pFrame->nb_samples = pCodecCtx->frame_size;
        pFrame->format = pCodecCtx->sample_fmt;
    
        //size maybe nums bytes of 1 fram
        size = av_samples_get_buffer_size(NULL, pCodecCtx->channels,pCodecCtx->frame_size,AV_SAMPLE_FMT_S32, 1);
        // 初始化buffer
        frame_buf[0] = av_malloc(size);
        if(frame_buf[0] == NULL)
        {
            DEBUG_LOG("frame_buf[0] malloc fail.");
            return NULL;
        }
    
        //Write Header
        ret = avformat_write_header(pFormatCtx, NULL);
        if (ret < 0)
        {
            DEBUG_LOG( "Error occurred when opening output file\n");
            return NULL;
        }
        av_new_packet(&pkt, size);
        while(1)
        {
            memset(frame_buf[0], 0, size);
            read(pipe_fd, frame_buf[0], size);
    
    #ifdef DEBUG_CODER_PCM
            //fixme test out32pcm
            fwrite(frame_buf[0], 1, size, pout_file);
    #endif
    
            //alloc fram->data
            av_freep(&pFrame->data[0]);
            ret = av_samples_alloc(pFrame->data, &pFrame->linesize[0],
                av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO), pFrame->nb_samples, AV_SAMPLE_FMT_FLTP, 0);
            if(ret < 0)
            {
                DEBUG_LOG("alloc samples error!");
                break;
            }
            //convert pcm
            dst_nb_samples = swr_convert(swr_ctx, pFrame->data, pFrame->nb_samples,
                (const uint8_t **)frame_buf, pFrame->nb_samples);
            if( dst_nb_samples < 0)
            {
                DEBUG_LOG("Convert pcm error!");
                break;
            }
    
    #ifdef DEBUG_CODER_PCM
            //DEBUG_LOG("#####size of pcm :%x", sizeof(pFrame->data[0]));
            //fixme test outpcm
            //data_size = av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO) * dst_nb_samples * av_get_bytes_per_sample(AV_SAMPLE_FMT_S16);
            //fwrite(pFrame->data[0], 1, data_size, pout_file);
    #endif
    
            //Encode
            got_frame = 0;
            ret = avcodec_encode_audio2(pCodecCtx, &pkt, pFrame, &got_frame);
            if(ret < 0)
            {
                DEBUG_LOG("Failed to encode!\n");
                return NULL ;
            }
    
            if (got_frame==1)
            {
                pkt.stream_index = audio_st->index;
    
                ret = av_interleaved_write_frame(pFormatCtx, &pkt);
                if(ret < 0)
                {
                    DEBUG_LOG("write pkt error");
                    break;
                }
                av_free_packet(&pkt);
            }
    
            if(g_coderEnd == true)
            {
                DEBUG_LOG("End coder thread");
                g_coderEnd = false;
                break;
            }
    
        }
    
        //Flush Encoder
        ret = flush_encoder(pFormatCtx,0);
        if (ret < 0) {
            DEBUG_LOG("Flushing encoder failed\n");
            return NULL ;
        }
    
    
        //Write Trailer
        av_write_trailer(pFormatCtx);
    
        //Clean
        close(pipe_fd);
        if (audio_st)
        {
            avcodec_close(audio_st->codec);
            av_free(pFrame);
            av_free(frame_buf[0]);
        }
        avio_close(pFormatCtx->pb);
        avformat_free_context(pFormatCtx);
    
    #ifdef DEBUG_CODER_PCM
        fclose(pout_file);
    #endif
    
        DEBUG_LOG("Exit coder thread");
        g_coder_thread = 0;
        UDP_UnLock();
        return NULL ;
    }

[http_blog.csdn.net_leixiaohua1020_article_details_25430449]: http://blog.csdn.net/leixiaohua1020/article/details/25430449
[SouthEast]: /images/20220617/24977b94b23246a19cb712ba664b70cb.png
[SouthEast 1]: /images/20220617/270553da330f4a38852d6851a987313b.png
[SouthEast 2]: /images/20220617/9ea2d0a996264acebdffa5a1462c8d36.png