Calculating Ogg Audio Duration in Go: A Step-by-Step Guide

func getOggDurationMs(reader io.Reader) (int64, error) {
    // Read the entire Ogg file into a byte slice
    data, err := io.ReadAll(reader)
    if err != nil {
        return 0, fmt.Errorf("error reading Ogg file: %w", err)
    }

    // Search for the "OggS" signature and calculate the length
    var length int64
    for i := len(data) - 14; i >= 0 && length == 0; i-- {
        if data[i] == 'O' && data[i+1] == 'g' && data[i+2] == 'g' && data[i+3] == 'S' {
            length = int64(readLittleEndianInt(data[i+6 : i+14]))
        }
    }

    // Search for the "vorbis" signature and calculate the rate
    var rate int64
    for i := 0; i < len(data)-14 && rate == 0; i++ {
        if data[i] == 'v' && data[i+1] == 'o' && data[i+2] == 'r' && data[i+3] == 'b' && data[i+4] == 'i' && data[i+5] == 's' {
            rate = int64(readLittleEndianInt(data[i+11 : i+15]))
        }
    }

    if length == 0 || rate == 0 {
        return 0, fmt.Errorf("could not find necessary information in Ogg file")
    }

    durationMs := length * 1000 / rate
    return durationMs, nil
}

func readLittleEndianInt(data []byte) int64 {
    return int64(uint32(data[0]) | uint32(data[1])<<8 | uint32(data[2])<<16 | uint32(data[3])<<24)
}