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pcm: changed location to codec

This commit is contained in:
Trek H 2019-04-09 15:42:44 +09:30
parent 2d15e98445
commit f597a04289
2 changed files with 263 additions and 0 deletions
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145
codec/pcm/pcm.go Normal file
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/*
NAME
pcm.go
DESCRIPTION
pcm.go contains functions for processing pcm.
AUTHOR
Trek Hopton <trek@ausocean.org>
LICENSE
pcm.go is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
It is free software: you can redistribute it and/or modify them
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
It is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License in gpl.txt.
If not, see [GNU licenses](http://www.gnu.org/licenses).
*/
package pcm
import (
"encoding/binary"
"fmt"
"github.com/yobert/alsa"
)
// Resample takes an alsa.Buffer (b) and resamples the pcm audio data to 'rate' Hz and returns the resulting pcm.
// If an error occurs, an error will be returned along with the original b's data.
// Notes:
// - Currently only downsampling is implemented and b's rate must be divisible by 'rate' or an error will occur.
// - If the number of bytes in b.Data is not divisible by the decimation factor (ratioFrom), the remaining bytes will
// not be included in the result. Eg. input of length 480002 downsampling 6:1 will result in output length 80000.
func Resample(b alsa.Buffer, rate int) ([]byte, error) {
fromRate := b.Format.Rate
if fromRate == rate {
return b.Data, nil
} else if fromRate < 0 {
return nil, fmt.Errorf("Unable to convert from: %v Hz", fromRate)
} else if rate < 0 {
return nil, fmt.Errorf("Unable to convert to: %v Hz", rate)
}
// The number of bytes in a sample.
var sampleLen int
switch b.Format.SampleFormat {
case alsa.S32_LE:
sampleLen = 4 * b.Format.Channels
case alsa.S16_LE:
sampleLen = 2 * b.Format.Channels
default:
return nil, fmt.Errorf("Unhandled ALSA format: %v", b.Format.SampleFormat)
}
inPcmLen := len(b.Data)
// Calculate sample rate ratio ratioFrom:ratioTo.
rateGcd := gcd(rate, fromRate)
ratioFrom := fromRate / rateGcd
ratioTo := rate / rateGcd
// ratioTo = 1 is the only number that will result in an even sampling.
if ratioTo != 1 {
return nil, fmt.Errorf("unhandled from:to rate ratio %v:%v: 'to' must be 1", ratioFrom, ratioTo)
}
newLen := inPcmLen / ratioFrom
result := make([]byte, 0, newLen)
// For each new sample to be generated, loop through the respective 'ratioFrom' samples in 'b.Data' to add them
// up and average them. The result is the new sample.
bAvg := make([]byte, sampleLen)
for i := 0; i < newLen/sampleLen; i++ {
var sum int
for j := 0; j < ratioFrom; j++ {
switch b.Format.SampleFormat {
case alsa.S32_LE:
sum += int(int32(binary.LittleEndian.Uint32(b.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
case alsa.S16_LE:
sum += int(int16(binary.LittleEndian.Uint16(b.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
}
}
avg := sum / ratioFrom
switch b.Format.SampleFormat {
case alsa.S32_LE:
binary.LittleEndian.PutUint32(bAvg, uint32(avg))
case alsa.S16_LE:
binary.LittleEndian.PutUint16(bAvg, uint16(avg))
}
result = append(result, bAvg...)
}
return result, nil
}
// StereoToMono returns raw mono audio data generated from only the left channel from
// the given stereo recording (ALSA buffer)
// if an error occurs, an error will be returned along with the original stereo data.
func StereoToMono(b alsa.Buffer) ([]byte, error) {
if b.Format.Channels == 1 {
return b.Data, nil
} else if b.Format.Channels != 2 {
return nil, fmt.Errorf("Audio is not stereo or mono, it has %v channels", b.Format.Channels)
}
var stereoSampleBytes int
switch b.Format.SampleFormat {
case alsa.S32_LE:
stereoSampleBytes = 8
case alsa.S16_LE:
stereoSampleBytes = 4
default:
return nil, fmt.Errorf("Unhandled ALSA format %v", b.Format.SampleFormat)
}
recLength := len(b.Data)
mono := make([]byte, recLength/2)
// Convert to mono: for each byte in the stereo recording, if it's in the first half of a stereo sample
// (left channel), add it to the new mono audio data.
var inc int
for i := 0; i < recLength; i++ {
if i%stereoSampleBytes < stereoSampleBytes/2 {
mono[inc] = b.Data[i]
inc++
}
}
return mono, nil
}
// gcd is used for calculating the greatest common divisor of two positive integers, a and b.
// assumes given a and b are positive.
func gcd(a, b int) int {
for b != 0 {
a, b = b, a%b
}
return a
}

118
codec/pcm/pcm_test.go Normal file
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/*
NAME
pcm_test.go
DESCRIPTION
pcm_test.go contains functions for testing the pcm package.
AUTHOR
Trek Hopton <trek@ausocean.org>
LICENSE
pcm_test.go is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
It is free software: you can redistribute it and/or modify them
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
It is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License in gpl.txt.
If not, see [GNU licenses](http://www.gnu.org/licenses).
*/
package pcm
import (
"bytes"
"io/ioutil"
"log"
"testing"
"github.com/yobert/alsa"
)
// TestResample tests the Resample function using a pcm file that contains audio of a freq. sweep.
// The output of the Resample function is compared with a file containing the expected result.
func TestResample(t *testing.T) {
inPath := "../../../test/test-data/av/input/sweep_400Hz_20000Hz_-3dBFS_5s_48khz.pcm"
expPath := "../../../test/test-data/av/output/sweep_400Hz_20000Hz_resampled_48to8kHz.pcm"
// Read input pcm.
inPcm, err := ioutil.ReadFile(inPath)
if err != nil {
log.Fatal(err)
}
format := alsa.BufferFormat{
Channels: 1,
Rate: 48000,
SampleFormat: alsa.S16_LE,
}
buf := alsa.Buffer{
Format: format,
Data: inPcm,
}
// Resample pcm.
resampled, err := Resample(buf, 8000)
if err != nil {
log.Fatal(err)
}
// Read expected resampled pcm.
exp, err := ioutil.ReadFile(expPath)
if err != nil {
log.Fatal(err)
}
// Compare result with expected.
if !bytes.Equal(resampled, exp) {
t.Error("Resampled data does not match expected result.")
}
}
// TestStereoToMono tests the StereoToMono function using a pcm file that contains stereo audio.
// The output of the StereoToMono function is compared with a file containing the expected mono audio.
func TestStereoToMono(t *testing.T) {
inPath := "../../../test/test-data/av/input/stereo_DTMF_tones.pcm"
expPath := "../../../test/test-data/av/output/mono_DTMF_tones.pcm"
// Read input pcm.
inPcm, err := ioutil.ReadFile(inPath)
if err != nil {
log.Fatal(err)
}
format := alsa.BufferFormat{
Channels: 2,
Rate: 44100,
SampleFormat: alsa.S16_LE,
}
buf := alsa.Buffer{
Format: format,
Data: inPcm,
}
// Convert audio.
mono, err := StereoToMono(buf)
if err != nil {
log.Fatal(err)
}
// Read expected mono pcm.
exp, err := ioutil.ReadFile(expPath)
if err != nil {
log.Fatal(err)
}
// Compare result with expected.
if !bytes.Equal(mono, exp) {
t.Error("Converted data does not match expected result.")
}
}