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