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pcm: simplified and improved efficiency of code.

This commit is contained in:
Trek H 2019-03-26 15:43:11 +10:30
parent 72f0b009fe
commit 9a9a38dbe1
3 changed files with 45 additions and 54 deletions
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72
audio/pcm/pcm.go
View File

@ -33,62 +33,62 @@ import (
"github.com/yobert/alsa"
)
// Resample takes an alsa.Buffer (fromBuf) and resamples the pcm audio data to 'toRate' Hz and returns the resulting pcm.
// If an error occurs, an error will be returned along with the original fromBuf's data.
// 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 fromBuf's rate must be divisible by toRate or an error will occur.
// - If the number of bytes in fromBuf.Data is not divisible by the decimation factor (ratioFrom), the remaining bytes will
// - 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(fromBuf alsa.Buffer, toRate int) ([]byte, error) {
fromRate := fromBuf.Format.Rate
if fromRate == toRate {
return fromBuf.Data, nil
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 fromBuf.Data, fmt.Errorf("Unable to convert from: %v Hz", fromRate)
} else if toRate < 0 {
return fromBuf.Data, fmt.Errorf("Unable to convert to: %v Hz", toRate)
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 fromBuf.Format.SampleFormat {
switch b.Format.SampleFormat {
case alsa.S32_LE:
sampleLen = 4 * fromBuf.Format.Channels
sampleLen = 4 * b.Format.Channels
case alsa.S16_LE:
sampleLen = 2 * fromBuf.Format.Channels
sampleLen = 2 * b.Format.Channels
default:
return fromBuf.Data, fmt.Errorf("Unhandled ALSA format: %v", fromBuf.Format.SampleFormat)
return nil, fmt.Errorf("Unhandled ALSA format: %v", b.Format.SampleFormat)
}
inPcmLen := len(fromBuf.Data)
inPcmLen := len(b.Data)
// Calculate sample rate ratio ratioFrom:ratioTo.
rateGcd := gcd(toRate, fromRate)
rateGcd := gcd(rate, fromRate)
ratioFrom := fromRate / rateGcd
ratioTo := toRate / rateGcd
ratioTo := rate / rateGcd
// ratioTo = 1 is the only number that will result in an even sampling.
if ratioTo != 1 {
return fromBuf.Data, fmt.Errorf("%v:%v is an unhandled from:to rate ratio. must be n:1 for some rate n", ratioFrom, ratioTo)
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 'fromBuf.Data' to add them
// 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 fromBuf.Format.SampleFormat {
switch b.Format.SampleFormat {
case alsa.S32_LE:
sum += int(int32(binary.LittleEndian.Uint32(fromBuf.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
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(fromBuf.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
sum += int(int16(binary.LittleEndian.Uint16(b.Data[(i*ratioFrom*sampleLen)+(j*sampleLen) : (i*ratioFrom*sampleLen)+((j+1)*sampleLen)])))
}
}
avg := sum / ratioFrom
bAvg := make([]byte, sampleLen)
switch fromBuf.Format.SampleFormat {
switch b.Format.SampleFormat {
case alsa.S32_LE:
binary.LittleEndian.PutUint32(bAvg, uint32(avg))
case alsa.S16_LE:
@ -102,24 +102,24 @@ func Resample(fromBuf alsa.Buffer, toRate int) ([]byte, error) {
// 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(stereoBuf alsa.Buffer) ([]byte, error) {
if stereoBuf.Format.Channels == 1 {
return stereoBuf.Data, nil
} else if stereoBuf.Format.Channels != 2 {
return stereoBuf.Data, fmt.Errorf("Audio is not stereo or mono, it has %v channels", stereoBuf.Format.Channels)
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 stereoBuf.Format.SampleFormat {
switch b.Format.SampleFormat {
case alsa.S32_LE:
stereoSampleBytes = 8
case alsa.S16_LE:
stereoSampleBytes = 4
default:
return stereoBuf.Data, fmt.Errorf("Unhandled ALSA format %v", stereoBuf.Format.SampleFormat)
return nil, fmt.Errorf("Unhandled ALSA format %v", b.Format.SampleFormat)
}
recLength := len(stereoBuf.Data)
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
@ -127,7 +127,7 @@ func StereoToMono(stereoBuf alsa.Buffer) ([]byte, error) {
var inc int
for i := 0; i < recLength; i++ {
if i%stereoSampleBytes < stereoSampleBytes/2 {
mono[inc] = stereoBuf.Data[i]
mono[inc] = b.Data[i]
inc++
}
}
@ -138,8 +138,8 @@ func StereoToMono(stereoBuf alsa.Buffer) ([]byte, error) {
// 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 {
if b != 0 {
return gcd(b, a%b)
for b != 0 {
a, b = b, a%b
}
return a
}

18
exp/pcm/resample/resample.go
View File

@ -39,18 +39,12 @@ import (
// This program accepts an input pcm file and outputs a resampled pcm file.
// Input and output file names, to and from sample rates, channels and sample format can be specified as arguments.
func main() {
var inPath string
var outPath string
var from int
var to int
var channels int
var sf string
flag.StringVar(&inPath, "in", "data.pcm", "file path of input data")
flag.StringVar(&outPath, "out", "resampled.pcm", "file path of output")
flag.IntVar(&from, "from", 48000, "sample rate of input file")
flag.IntVar(&to, "to", 8000, "sample rate of output file")
flag.IntVar(&channels, "ch", 1, "number of channels in input file")
flag.StringVar(&sf, "sf", "S16_LE", "sample format of input audio, eg. S16_LE")
var inPath = *flag.String("in", "data.pcm", "file path of input data")
var outPath = *flag.String("out", "resampled.pcm", "file path of output")
var from = *flag.Int("from", 48000, "sample rate of input file")
var to = *flag.Int("to", 8000, "sample rate of output file")
var channels = *flag.Int("ch", 1, "number of channels in input file")
var sf = *flag.String("sf", "S16_LE", "sample format of input audio, eg. S16_LE")
flag.Parse()
// Read pcm.

9
exp/pcm/stereo-to-mono/stereo-to-mono.go
View File

@ -39,12 +39,9 @@ import (
// This program accepts an input pcm file and outputs a resampled pcm file.
// Input and output file names, to and from sample rates, channels and sample format can be specified as arguments.
func main() {
var inPath string
var outPath string
var sf string
flag.StringVar(&inPath, "in", "data.pcm", "file path of input data")
flag.StringVar(&outPath, "out", "mono.pcm", "file path of output")
flag.StringVar(&sf, "sf", "S16_LE", "sample format of input audio, eg. S16_LE")
var inPath = *flag.String("in", "data.pcm", "file path of input data")
var outPath = *flag.String("out", "mono.pcm", "file path of output")
var sf = *flag.String("sf", "S16_LE", "sample format of input audio, eg. S16_LE")
flag.Parse()
// Read pcm.