clipper/backend/media/peak_progress.go

111 lines
2.6 KiB
Go

package media
import (
"bytes"
"encoding/binary"
"fmt"
"io"
)
type FetchPeaksProgress struct {
percentComplete float32
Peaks []int16
}
// fetchPeaksIterator accepts a byte stream containing little endian
// signed int16s and, given a target number of bins, emits a stream of peaks
// corresponding to each channel of the audio data.
type fetchPeaksIterator struct {
channels int
framesPerBin int
samples []int16
currPeaks []int16
currCount int
total int
progress chan FetchPeaksProgress
errorChan chan error
}
// TODO: validate inputs, debugging is confusing otherwise
func newFetchPeaksIterator(expFrames int64, channels, numBins int) *fetchPeaksIterator {
return &fetchPeaksIterator{
channels: channels,
framesPerBin: int(expFrames / int64(numBins)),
samples: make([]int16, 8_192),
currPeaks: make([]int16, channels),
progress: make(chan FetchPeaksProgress),
errorChan: make(chan error, 1),
}
}
func (w *fetchPeaksIterator) Abort(err error) {
w.errorChan <- err
}
func (w *fetchPeaksIterator) Close() error {
close(w.progress)
return nil
}
func (w *fetchPeaksIterator) Write(p []byte) (int, error) {
// expand our target slice if it is of insufficient size:
numSamples := len(p) / SizeOfInt16
if len(w.samples) < numSamples {
w.samples = append(w.samples, make([]int16, numSamples-len(w.samples))...)
}
samples := w.samples[:numSamples]
if err := binary.Read(bytes.NewReader(p), binary.LittleEndian, samples); err != nil {
return 0, fmt.Errorf("error parsing samples: %v", err)
}
for i := 0; i < len(samples); i += w.channels {
for j := 0; j < w.channels; j++ {
samp := samples[i+j]
if samp < 0 {
samp = -samp
}
if samp > w.currPeaks[j] {
w.currPeaks[j] = samp
}
}
w.currCount++
if w.currCount == w.framesPerBin {
w.nextBin()
}
}
return len(p), nil
}
func (w *fetchPeaksIterator) nextBin() {
var progress FetchPeaksProgress
// TODO: avoid an allocation?
progress.Peaks = append(progress.Peaks, w.currPeaks...)
w.progress <- progress
w.currCount = 0
// log.Printf("got peak for %d frames, which is equal to target of %d frames per bin, %d total bins processed, peaks: %+v", w.currCount, w.framesPerBin, w.total+1, w.currPeaks)
for i := 0; i < len(w.currPeaks); i++ {
w.currPeaks[i] = 0
}
w.total++
}
func (w *fetchPeaksIterator) Next() (FetchPeaksProgress, error) {
for {
select {
case progress, ok := <-w.progress:
if !ok {
return FetchPeaksProgress{}, io.EOF
}
return FetchPeaksProgress{Peaks: progress.Peaks}, nil
case err := <-w.errorChan:
return FetchPeaksProgress{}, fmt.Errorf("error waiting for progress: %v", err)
}
}
}