100 lines
2.5 KiB
Go
100 lines
2.5 KiB
Go
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package media
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import (
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"encoding/binary"
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"os"
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)
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const SizeOfInt16 = 2
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// MediaSet represents the media and metadata associated with a single media
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// resource (for example, a YouTube video).
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type MediaSet struct {
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ID string `json:"id"`
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Source string `json:"source"`
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Bytes int64 `json:"bytes"`
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Channels int `json:"channels"`
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Frames int64 `json:"frames"`
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SampleRate int `json:"sample_rate"`
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exists bool
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}
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func (m *MediaSet) RawAudioPath() string { return fmt.Sprintf("cache/%s.raw", m.ID) }
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func (m *MediaSet) EncodedAudioPath() string { return fmt.Sprintf("cache/%s.m4a", m.ID) }
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func (m *MediaSet) VideoPath() string { return fmt.Sprintf("cache/%s.mp4", m.ID) }
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func (m *MediaSet) MetadataPath() string { return fmt.Sprintf("cache/%s.json", m.ID) }
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func (m *MediaSet) Exists() bool {
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if m.exists {
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return true
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}
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if _, err := os.Stat(m.MetadataPath()); err == nil {
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m.exists = true
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return true
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}
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return false
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}
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func (m *MediaSet) Load() error {
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metadataFile, err := os.Open(m.MetadataPath())
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if err != nil {
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return fmt.Errorf("error opening metadata file: %v", err)
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}
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defer func() { _ = metadataFile.Close() }()
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if err := json.NewDecoder(metadataFile).Decode(m); err != nil {
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return fmt.Errorf("error decoding metadata: %v", err)
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}
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return nil
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}
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func (m *MediaSet) Peaks(start, end int64, numBins int) ([][]int16, error) {
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if !m.Exists() {
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return nil, errors.New("cannot compute peaks for non-existent MediaSet")
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}
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var err error
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fptr, err := os.Open(m.RawAudioPath())
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if err != nil {
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return nil, fmt.Errorf("audio open error: %v", err)
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}
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defer fptr.Close()
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startByte := start * int64(m.Channels) * SizeOfInt16
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if _, err = fptr.Seek(startByte, io.SeekStart); err != nil {
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return nil, fmt.Errorf("audio seek error: %v", err)
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}
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numFrames := end - start
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framesPerBin := numFrames / int64(numBins)
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peaks := make([][]int16, m.Channels)
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for i := 0; i < m.Channels; i++ {
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peaks[i] = make([]int16, numBins)
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}
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samples := make([]int16, framesPerBin*int64(m.Channels))
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for binNum := 0; binNum < numBins; binNum++ {
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if err := binary.Read(fptr, binary.LittleEndian, samples); err != nil {
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return nil, fmt.Errorf("error reading samples: %v", err)
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}
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for i, samp := range samples {
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if samp < 0 {
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samp = -samp
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}
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chanIndex := i % m.Channels
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if samp > peaks[chanIndex][binNum] {
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peaks[chanIndex][binNum] = samp
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}
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}
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}
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return peaks, nil
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}
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