Esp32 things (VIII): music playing function of function development

     This article does not discuss online music playing , If the whole system only has the function of online music playing , There should be no problem with system resources . At the same time, it can also support a variety of audio CODEC. 

    For local audio file playback , because ESP32 Chip systems usually have limited storage and memory resources , If there is no plug-in SRAM, Only 512KB Available memory , For example, our project only has 512KB Of memory , and 4MB Of Flash, For projects like this , If audio playback is required , Then we must consider ：

     How files are stored ？ Is there enough memory ？ Obviously, the compressed audio file will be smaller , however Codec More memory is required for decoding , Whether the system memory can meet the requirements . This project was initially preserved mp3 File format , With Bluetooth enabled , Bluetooth consumes a lot of memory , There is little memory left in the system , however mp3 The decoder used in decoding needs to consume about ten K Of memory , Memory is tight , Later, due to our audio resources   less , Just swap space for memory , Just use wav File format , The audio is not compressed , Direct read file write I2S.

1、mp3 Play

use mad decoder . You can find many videos on the Internet mp3 Example , I won't enumerate the code here .

2、Raw wav File playback

/* read 4 bytes of data from wav file */

int read4bytes(uint8_t *pos, uint32_t *chunkId){

  memcpy((uint8_t *)chunkId, pos, sizeof(uint32_t));

  return sizeof(uint32_t);

}

/* these are function to process wav file */

int readRiff(uint8_t *pos, wavRiff_t *wavRiff){

  memcpy((uint8_t *)wavRiff, pos, sizeof(wavRiff_t));

  return sizeof(wavRiff_t);

}

int readProps(uint8_t *pos, wavProperties_t *wavProps){

  memcpy((uint8_t *)wavProps, pos, sizeof(wavProperties_t));

  return sizeof(wavProperties_t);

}

void play_wav_files(uint8_t *fstart, uint8_t *fend)

{

    //uint8_t *pos = fstart;

    //renderer_start();

    uint8_t *pos = fstart;

    //renderer_zero_dma_buffer();

    /*int n = 0;

    headerState_t state = HEADER_RIFF;

    wavProperties_t wavProps;

    while (pos < fend) {

        switch(state){

            case HEADER_RIFF: {

                wavRiff_t wavRiff;

                n = readRiff(pos, &wavRiff);

                if(n == sizeof(wavRiff_t)){

                    if(wavRiff.chunkID == CCCC('R', 'I', 'F', 'F') && wavRiff.format == CCCC('W', 'A', 'V', 'E')){

                        state = HEADER_FMT;

                        ESP_LOGI(TAG, "HEADER_RIFF");

                    }

                }

                pos += n;

                break;

            }

            case HEADER_FMT:

                n = readProps(pos, &wavProps);

                if(n == sizeof(wavProperties_t)){

                    state = HEADER_DATA;

                }

                pos += n;

                break;

            case HEADER_DATA:{

                uint32_t chunkId, chunkSize;

                n = read4bytes(pos, &chunkId);

                if(n == 4){

                    if(chunkId == CCCC('d', 'a', 't', 'a')){

                        ESP_LOGI(TAG, "HEADER_DATA");

                    }

                }

                pos += n;

                n = read4bytes(pos, &chunkSize);

                if(n == 4){

                    ESP_LOGI(TAG, "prepare data");

                    state = DATA;

                }

                pos += n;

                wav_buffer_fmt.sample_rate = wavProps.sampleRate;

                wav_buffer_fmt.num_channels = wavProps.numChannels;

                break;*/

                /* after processing wav file, it is time to process music data */

             }

            case DATA:{

                char data[2];

                memcpy(data, pos , 2);

                pos += 2;

                render_samples(data, 2, &wav_buffer_fmt);

                if(fend - pos < 2 ) {

                    ESP_LOGE(TAG, "<<<<<<<<<<<<<<<< Invalid file len <<<<<<<<<<<<<<<");

                    pos = fend;

                }

                break;

            }

        }

    }

    renderer_zero_dma_buffer();

}