ESP32开发（2）esp-adf：play_mp3例程简单分析

esp-adf

此套框架提供了一种使用流、编解码器和音频处理函数等元件开发音频应用程序的方法。

该框架是通过将元件组合成管道来开发音频应用程序。如下图所示：

将MP3解码器和I2S流两个元件添加进音频管道，解码器的输入是MP3文件数据流，I2S流将解码后的音频数据输出到片外，各应用程序之间通过事件接口通信。

play_mp3_example.c

get-started / play_mp3是此框架的最基本的例程之一，使用了MP3解码器和I2S流两个元件，我们通过分析这个例程来学习这套框架的使用。
初次接触这套框架，只是大概有个思路，有错在所难免，望见谅

/*读mp3文件的回调函数*/
int mp3_music_read_cb(audio_element_handle_t el, char *buf, int len, TickType_t wait_time, void *ctx)
{
    static int mp3_pos;
    int read_size = adf_music_mp3_end - adf_music_mp3_start - mp3_pos;
    if (read_size == 0) {
        return AEL_IO_DONE;
    } else if (len < read_size) {
        read_size = len;
    }
    memcpy(buf, adf_music_mp3_start + mp3_pos, read_size);
    mp3_pos += read_size;
    return read_size;
}

void app_main(void)
{
     //定义一个音频处理管道
    audio_pipeline_handle_t pipeline;
    //因为是实现本地播放，只需定义i2s流和MP3解码两个元件
    audio_element_handle_t i2s_stream_writer, mp3_decoder;
    //关闭非必要显示
    esp_log_level_set("*", ESP_LOG_WARN);
    esp_log_level_set(TAG, ESP_LOG_INFO);
    ESP_LOGI(TAG, "[ 1 ] Start audio codec chip");
    //根据不同硬件版本进行硬件初始化
#if (CONFIG_ESP_LYRAT_V4_3_BOARD || CONFIG_ESP_LYRAT_V4_2_BOARD)
    audio_hal_codec_config_t audio_hal_codec_cfg = AUDIO_HAL_ES8388_DEFAULT();
    audio_hal_handle_t hal = audio_hal_init(&audio_hal_codec_cfg, 0);
#endif
#if (CONFIG_ESP_LYRATD_MSC_V2_1_BOARD || CONFIG_ESP_LYRATD_MSC_V2_2_BOARD)
    audio_hal_codec_config_t audio_hal_codec_cfg = AUDIO_HAL_ZL38063_DEFAULT();
    audio_hal_handle_t hal = audio_hal_init(&audio_hal_codec_cfg, 2);
#endif
	//打开解码驱动
    audio_hal_ctrl_codec(hal, AUDIO_HAL_CODEC_MODE_DECODE, AUDIO_HAL_CTRL_START);
    ESP_LOGI(TAG, "[ 2 ] Create audio pipeline, add all elements to pipeline, and subscribe pipeline event");
    //管道初始化
    audio_pipeline_cfg_t pipeline_cfg = DEFAULT_AUDIO_PIPELINE_CONFIG();
    pipeline = audio_pipeline_init(&pipeline_cfg);
    mem_assert(pipeline);//？？？
    ESP_LOGI(TAG, "[2.1] Create mp3 decoder to decode mp3 file and set custom read callback");
    //解码器初始化
    mp3_decoder_cfg_t mp3_cfg = DEFAULT_MP3_DECODER_CONFIG();
    mp3_decoder = mp3_decoder_init(&mp3_cfg);
    //设置解码回调函数
    audio_element_set_read_cb(mp3_decoder, mp3_music_read_cb, NULL);
    ESP_LOGI(TAG, "[2.2] Create i2s stream to write data to codec chip");
    //I2S流初始化
    i2s_stream_cfg_t i2s_cfg = I2S_STREAM_CFG_DEFAULT();
    i2s_cfg.type = AUDIO_STREAM_WRITER;
    i2s_cfg.i2s_config.sample_rate = 48000;
    i2s_stream_writer = i2s_stream_init(&i2s_cfg);
    ESP_LOGI(TAG, "[2.3] Register all elements to audio pipeline");
    //注册元件
    audio_pipeline_register(pipeline, mp3_decoder, "mp3");
    audio_pipeline_register(pipeline, i2s_stream_writer, "i2s");
    ESP_LOGI(TAG, "[2.4] Link it together [mp3_music_read_cb]-->mp3_decoder-->i2s_stream-->[codec_chip]");
#if (CONFIG_ESP_LYRAT_V4_3_BOARD || CONFIG_ESP_LYRAT_V4_2_BOARD)
	//连接管内元件
    audio_pipeline_link(pipeline, (const char *[]) {"mp3", "i2s"}, 2);
#endif
    /**Zl38063 does not support 44.1KHZ frequency, so resample needs to be used to convert files to other rates.
     * You can transfer to 16kHZ or 48kHZ.
     */
#if (CONFIG_ESP_LYRATD_MSC_V2_1_BOARD || CONFIG_ESP_LYRATD_MSC_V2_2_BOARD)
    rsp_filter_cfg_t rsp_cfg = DEFAULT_RESAMPLE_FILTER_CONFIG();
    rsp_cfg.src_rate = 44100;
    rsp_cfg.src_ch = 2;
    rsp_cfg.dest_rate = 48000;
    rsp_cfg.dest_ch = 2;
    rsp_cfg.type = AUDIO_CODEC_TYPE_DECODER;
    audio_element_handle_t filter = rsp_filter_init(&rsp_cfg);
    audio_pipeline_register(pipeline, filter, "filter");
    audio_pipeline_link(pipeline, (const char *[]) {"mp3", "filter", "i2s"}, 3);
#endif
    ESP_LOGI(TAG, "[ 3 ] Setup event listener");
    //音频解码事件初始化
    audio_event_iface_cfg_t evt_cfg = AUDIO_EVENT_IFACE_DEFAULT_CFG();
    audio_event_iface_handle_t evt = audio_event_iface_init(&evt_cfg);
    ESP_LOGI(TAG, "[3.1] Listening event from all elements of pipeline");
    //监听管道事件
    audio_pipeline_set_listener(pipeline, evt);
    ESP_LOGI(TAG, "[ 4 ] Start audio_pipeline");
    //运行管道
    audio_pipeline_run(pipeline);
	/*
	主循环有三个判断:
	判断1：判断事件接口是否定义成功，若成功，ret应当有效。
	判断2：判断当前是否处于解码阶段，获取解码器相关信息，并显示，然后设置i2s数据流相关参数。
	判断3：判断是否处于i2s数据流阶段，并且data已停止。退出循环。
	*/
    while (1) {
    	//获取事件消息，如果事件定义过了，就去读取事件消息
        audio_event_iface_msg_t msg;
        esp_err_t ret = audio_event_iface_listen(evt, &msg, portMAX_DELAY);
        if (ret != ESP_OK) {
            ESP_LOGE(TAG, "[ * ] Event interface error : %d", ret);
            continue;
        }
		//获取MP3解码器的的消息指针，并在其后显示相关信息
        if (msg.source_type == AUDIO_ELEMENT_TYPE_ELEMENT && msg.source == (void *) mp3_decoder
            && msg.cmd == AEL_MSG_CMD_REPORT_MUSIC_INFO) {
            audio_element_info_t music_info = {0};
            audio_element_getinfo(mp3_decoder, &music_info);
            ESP_LOGI(TAG, "[ * ] Receive music info from mp3 decoder, sample_rates=%d, bits=%d, ch=%d",
                     music_info.sample_rates, music_info.bits, music_info.channels);
			//根据上面读取到的信息，设置i2s流
            audio_element_setinfo(i2s_stream_writer, &music_info);
            /* Es8388 and es8374 use this function to set I2S and codec to the same frequency as the music file, and zl38063
             * does not need this step because the data has been resampled.*/
        #if (CONFIG_ESP_LYRAT_V4_3_BOARD || CONFIG_ESP_LYRAT_V4_2_BOARD)
        	//设置i2s流相关参数
            i2s_stream_set_clk(i2s_stream_writer, music_info.sample_rates , music_info.bits, music_info.channels);
        #endif
            continue;
        }
        /* Stop when the last pipeline element (i2s_stream_writer in this case) receives stop event */
        if (msg.source_type == AUDIO_ELEMENT_TYPE_ELEMENT && msg.source == (void *) i2s_stream_writer
            && msg.cmd == AEL_MSG_CMD_REPORT_STATUS && (int) msg.data == AEL_STATUS_STATE_STOPPED) {
            break;
        }
    }
    ESP_LOGI(TAG, "[ 5 ] Stop audio_pipeline");
    //停止运行管道
    audio_pipeline_terminate(pipeline);
	//解注册元件
    audio_pipeline_unregister(pipeline, mp3_decoder);
    audio_pipeline_unregister(pipeline, i2s_stream_writer);
	//移除监听
    /* Terminate the pipeline before removing the listener */
    audio_pipeline_remove_listener(pipeline);
    /* Make sure audio_pipeline_remove_listener is called before destroying event_iface */
    //打断事件
    audio_event_iface_destroy(evt);
    /* Release all resources */
    //再次解注册元件？？？
    audio_pipeline_unregister(pipeline, i2s_stream_writer);
    audio_pipeline_unregister(pipeline, mp3_decoder);
#if (CONFIG_ESP_LYRATD_MSC_V2_1_BOARD || CONFIG_ESP_LYRATD_MSC_V2_2_BOARD)
	//解注册滤波器
    audio_pipeline_unregister(pipeline, filter);
    //解定义滤波器
    audio_element_deinit(filter);
#endif
	//解定义管道
    audio_pipeline_deinit(pipeline);
    //解定义元件
    audio_element_deinit(i2s_stream_writer);
    audio_element_deinit(mp3_decoder);
}