mirror of https://bitbucket.org/ausocean/av.git
pcm: changed location to codec
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Trek H
parent
2d15e98445
commit
f597a04289
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/*
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NAME
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pcm.go
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DESCRIPTION
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pcm.go contains functions for processing pcm.
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AUTHOR
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Trek Hopton <trek@ausocean.org>
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LICENSE
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pcm.go is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License in gpl.txt.
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If not, see [GNU licenses](http://www.gnu.org/licenses).
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*/
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package pcm
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import (
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"encoding/binary"
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"fmt"
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"github.com/yobert/alsa"
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)
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// Resample takes an alsa.Buffer (b) and resamples the pcm audio data to 'rate' Hz and returns the resulting pcm.
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// If an error occurs, an error will be returned along with the original b's data.
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// Notes:
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// - Currently only downsampling is implemented and b's rate must be divisible by 'rate' or an error will occur.
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// - If the number of bytes in b.Data is not divisible by the decimation factor (ratioFrom), the remaining bytes will
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// not be included in the result. Eg. input of length 480002 downsampling 6:1 will result in output length 80000.
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func Resample(b alsa.Buffer, rate int) ([]byte, error) {
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fromRate := b.Format.Rate
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if fromRate == rate {
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return b.Data, nil
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} else if fromRate < 0 {
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return nil, fmt.Errorf("Unable to convert from: %v Hz", fromRate)
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} else if rate < 0 {
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return nil, fmt.Errorf("Unable to convert to: %v Hz", rate)
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}
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// The number of bytes in a sample.
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var sampleLen int
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switch b.Format.SampleFormat {
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case alsa.S32_LE:
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sampleLen = 4 * b.Format.Channels
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case alsa.S16_LE:
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sampleLen = 2 * b.Format.Channels
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default:
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return nil, fmt.Errorf("Unhandled ALSA format: %v", b.Format.SampleFormat)
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}
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inPcmLen := len(b.Data)
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// Calculate sample rate ratio ratioFrom:ratioTo.
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rateGcd := gcd(rate, fromRate)
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ratioFrom := fromRate / rateGcd
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ratioTo := rate / rateGcd
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// ratioTo = 1 is the only number that will result in an even sampling.
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if ratioTo != 1 {
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return nil, fmt.Errorf("unhandled from:to rate ratio %v:%v: 'to' must be 1", ratioFrom, ratioTo)
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}
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newLen := inPcmLen / ratioFrom
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result := make([]byte, 0, newLen)
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// For each new sample to be generated, loop through the respective 'ratioFrom' samples in 'b.Data' to add them
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// up and average them. The result is the new sample.
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bAvg := make([]byte, sampleLen)
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for i := 0; i < newLen/sampleLen; i++ {
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var sum int
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for j := 0; j < ratioFrom; j++ {
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switch b.Format.SampleFormat {
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case alsa.S32_LE:
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sum += int(int32(binary.LittleEndian.Uint32(b.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
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case alsa.S16_LE:
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sum += int(int16(binary.LittleEndian.Uint16(b.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
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}
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}
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avg := sum / ratioFrom
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switch b.Format.SampleFormat {
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case alsa.S32_LE:
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binary.LittleEndian.PutUint32(bAvg, uint32(avg))
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case alsa.S16_LE:
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binary.LittleEndian.PutUint16(bAvg, uint16(avg))
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}
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result = append(result, bAvg...)
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}
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return result, nil
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}
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// StereoToMono returns raw mono audio data generated from only the left channel from
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// the given stereo recording (ALSA buffer)
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// if an error occurs, an error will be returned along with the original stereo data.
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func StereoToMono(b alsa.Buffer) ([]byte, error) {
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if b.Format.Channels == 1 {
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return b.Data, nil
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} else if b.Format.Channels != 2 {
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return nil, fmt.Errorf("Audio is not stereo or mono, it has %v channels", b.Format.Channels)
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}
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var stereoSampleBytes int
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switch b.Format.SampleFormat {
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case alsa.S32_LE:
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stereoSampleBytes = 8
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case alsa.S16_LE:
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stereoSampleBytes = 4
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default:
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return nil, fmt.Errorf("Unhandled ALSA format %v", b.Format.SampleFormat)
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}
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recLength := len(b.Data)
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mono := make([]byte, recLength/2)
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// Convert to mono: for each byte in the stereo recording, if it's in the first half of a stereo sample
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// (left channel), add it to the new mono audio data.
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var inc int
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for i := 0; i < recLength; i++ {
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if i%stereoSampleBytes < stereoSampleBytes/2 {
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mono[inc] = b.Data[i]
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inc++
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}
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}
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return mono, nil
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}
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// gcd is used for calculating the greatest common divisor of two positive integers, a and b.
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// assumes given a and b are positive.
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func gcd(a, b int) int {
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for b != 0 {
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a, b = b, a%b
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}
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return a
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}
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@ -0,0 +1,118 @@
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/*
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NAME
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pcm_test.go
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DESCRIPTION
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pcm_test.go contains functions for testing the pcm package.
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AUTHOR
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Trek Hopton <trek@ausocean.org>
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LICENSE
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pcm_test.go is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License in gpl.txt.
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If not, see [GNU licenses](http://www.gnu.org/licenses).
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*/
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package pcm
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import (
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"bytes"
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"io/ioutil"
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"log"
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"testing"
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"github.com/yobert/alsa"
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)
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// TestResample tests the Resample function using a pcm file that contains audio of a freq. sweep.
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// The output of the Resample function is compared with a file containing the expected result.
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func TestResample(t *testing.T) {
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inPath := "../../../test/test-data/av/input/sweep_400Hz_20000Hz_-3dBFS_5s_48khz.pcm"
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expPath := "../../../test/test-data/av/output/sweep_400Hz_20000Hz_resampled_48to8kHz.pcm"
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// Read input pcm.
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inPcm, err := ioutil.ReadFile(inPath)
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if err != nil {
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log.Fatal(err)
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}
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format := alsa.BufferFormat{
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Channels: 1,
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Rate: 48000,
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SampleFormat: alsa.S16_LE,
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}
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buf := alsa.Buffer{
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Format: format,
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Data: inPcm,
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}
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// Resample pcm.
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resampled, err := Resample(buf, 8000)
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if err != nil {
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log.Fatal(err)
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}
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// Read expected resampled pcm.
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exp, err := ioutil.ReadFile(expPath)
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if err != nil {
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log.Fatal(err)
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}
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// Compare result with expected.
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if !bytes.Equal(resampled, exp) {
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t.Error("Resampled data does not match expected result.")
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}
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}
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// TestStereoToMono tests the StereoToMono function using a pcm file that contains stereo audio.
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// The output of the StereoToMono function is compared with a file containing the expected mono audio.
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func TestStereoToMono(t *testing.T) {
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inPath := "../../../test/test-data/av/input/stereo_DTMF_tones.pcm"
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expPath := "../../../test/test-data/av/output/mono_DTMF_tones.pcm"
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// Read input pcm.
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inPcm, err := ioutil.ReadFile(inPath)
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if err != nil {
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log.Fatal(err)
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}
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format := alsa.BufferFormat{
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Channels: 2,
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Rate: 44100,
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SampleFormat: alsa.S16_LE,
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}
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buf := alsa.Buffer{
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Format: format,
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Data: inPcm,
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}
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// Convert audio.
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mono, err := StereoToMono(buf)
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if err != nil {
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log.Fatal(err)
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}
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// Read expected mono pcm.
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exp, err := ioutil.ReadFile(expPath)
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if err != nil {
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log.Fatal(err)
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}
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// Compare result with expected.
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if !bytes.Equal(mono, exp) {
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t.Error("Converted data does not match expected result.")
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}
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}
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