@siteed/expo-audio-studio
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Comprehensive audio processing library for React Native and Expo with recording, analysis, visualization, and streaming capabilities across iOS, Android, and web
84 lines • 4.06 kB
JavaScript
// packages/expo-audio-stream/src/utils/writeWavHeader.ts
/**
* Writes or updates a WAV (RIFF) header based on the provided options.
*
* This function can be used in three ways:
* 1. To create a standalone WAV header (when no buffer is provided).
* 2. To create a WAV header and combine it with existing audio data (when a buffer without a header is provided).
* 3. To update an existing WAV header in the provided buffer.
*
* For streaming audio where the final size is unknown, this function sets the size fields
* to the maximum 32-bit value (0xFFFFFFFF). These can be updated later using the
* `updateWavHeaderSize` function once the final size is known.
*
* @param options - The options for creating or updating the WAV header.
* @returns An ArrayBuffer containing the WAV header, or the header combined with the provided audio data.
*
* @throws {Error} Throws an error if the provided options are invalid or if the buffer is too small.
*/
export const writeWavHeader = ({ buffer, sampleRate, numChannels, bitDepth, isFloat = bitDepth === 32, // Default to float for 32-bit
}) => {
// For 32-bit float, we use format 3, otherwise format 1 for PCM
const audioFormat = isFloat ? 3 : 1; // 3 = IEEE float, 1 = PCM
const bytesPerSample = bitDepth / 8;
const blockAlign = numChannels * bytesPerSample;
const byteRate = sampleRate * blockAlign;
// Function to write a string to the DataView
const writeString = (view, offset, string) => {
for (let i = 0; i < string.length; i++) {
view.setUint8(offset + i, string.charCodeAt(i));
}
};
// Function to write or update the header
const writeHeader = (view, dataSize = 0xffffffff) => {
// RIFF chunk descriptor
writeString(view, 0, 'RIFF'); // ChunkID
view.setUint32(4, 36 + dataSize, true); // ChunkSize: 4 + (8 + 16) + (8 + dataSize)
writeString(view, 8, 'WAVE'); // Format
// "fmt " sub-chunk
writeString(view, 12, 'fmt '); // Subchunk1ID
view.setUint32(16, 16, true); // Subchunk1Size (16 for PCM/Float)
view.setUint16(20, audioFormat, true); // AudioFormat (3 for float, 1 for PCM)
view.setUint16(22, numChannels, true); // NumChannels
view.setUint32(24, sampleRate, true); // SampleRate
view.setUint32(28, byteRate, true); // ByteRate = SampleRate * NumChannels * BitsPerSample/8
view.setUint16(32, blockAlign, true); // BlockAlign = NumChannels * BitsPerSample/8
view.setUint16(34, bitDepth, true); // BitsPerSample
// "data" sub-chunk
writeString(view, 36, 'data'); // Subchunk2ID
view.setUint32(40, dataSize, true); // Subchunk2Size = NumSamples * NumChannels * BitsPerSample/8
};
if (buffer) {
// Handle existing buffer
// Check for minimum size
if (buffer.byteLength < 44) {
throw new Error('Buffer is too small to contain a valid WAV header');
}
const view = new DataView(buffer);
// Check if the buffer already has a WAV header by looking for "RIFF" at the start
const existingHeader = view.getUint32(0, false) === 0x52494646; // "RIFF" in ASCII
if (existingHeader) {
// Update the existing header
writeHeader(view, buffer.byteLength - 44);
return buffer;
}
else {
// Create a new buffer with header + data
const newBuffer = new ArrayBuffer(44 + buffer.byteLength);
const newView = new DataView(newBuffer);
// Write header to new buffer
writeHeader(newView, buffer.byteLength);
// Copy audio data after header
new Uint8Array(newBuffer).set(new Uint8Array(buffer), 44);
return newBuffer;
}
}
else {
// Create standalone header
const headerBuffer = new ArrayBuffer(44);
const view = new DataView(headerBuffer);
writeHeader(view);
return headerBuffer;
}
};
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