128 lines
2.6 KiB
Go
128 lines
2.6 KiB
Go
// Package media contains logic related to parsing and segmenting media
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// streams, such as MP3 streams.
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//
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// It is depended upon by the playlist package.
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package media
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import (
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"bytes"
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"io"
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"log"
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"time"
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"github.com/tcolgate/mp3"
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)
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const DefaultTargetDuration = 3 * time.Second
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type Segmenter interface {
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Segment(r io.Reader) (chan *Segment, error)
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}
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type SegmentPublisher interface {
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Publish(s *Segment) (string, error)
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}
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type Segment struct {
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duration time.Duration
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targetDuration time.Duration
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data *bytes.Buffer
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}
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// Initialize a new Segment struct. The capacity is the initial maximum capacity of the internal
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// buffer, in bytes. It should be initialized with a value greater than the expected maximum buffer size,
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// depending on the implementation.
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func NewSegment(targetDuration time.Duration, capacity int) *Segment {
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return &Segment{
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data: bytes.NewBuffer(make([]byte, 0, capacity)),
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duration: 0,
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targetDuration: targetDuration,
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}
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}
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func (s *Segment) ReadFrom(r io.Reader) (n int64, err error) {
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return s.data.ReadFrom(r)
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}
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func (s *Segment) IncrementDuration(d time.Duration) time.Duration {
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s.duration += d
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return s.duration
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}
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func (s *Segment) CanWrite(d time.Duration) bool {
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return s.targetDuration-s.duration >= d
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}
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func (s *Segment) Duration() time.Duration {
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return s.duration
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}
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func (s *Segment) Len() int {
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return s.data.Len()
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}
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type MP3Segmenter struct {
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decoder *mp3.Decoder
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}
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func (s *MP3Segmenter) Segment(r io.Reader) (chan *Segment, error) {
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c := make(chan *Segment)
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go func() {
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d := mp3.NewDecoder(r)
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var (
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v mp3.Frame
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skipped int
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)
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var (
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s *Segment
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)
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for {
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if err := d.Decode(&v, &skipped); err != nil {
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if err == io.EOF {
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break
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}
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log.Fatal(err)
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}
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if s != nil && !s.CanWrite(v.Duration()) {
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// publish the current segment, and initialize a new one.
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c <- s
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s = nil
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}
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if s == nil {
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// TODO what is a good initial capacity?
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s = NewSegment(DefaultTargetDuration, 1024)
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}
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n, err := s.ReadFrom(v.Reader())
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if err != nil {
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log.Fatal(err) // TODO: some proper error handling
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}
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if n != int64(v.Size()) {
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// TODO would this ever happen? What should IncrementDuration be called with?
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log.Fatal("unexpeced frame size, want = ", v.Size(), "got = ", n)
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}
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s.IncrementDuration(v.Duration())
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}
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}()
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return c, nil
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}
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func NewMP3Segmenter() *MP3Segmenter {
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return &MP3Segmenter{}
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}
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type FakePublisher struct{}
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func (p *FakePublisher) Publish(s *Segment) (string, error) {
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return "https://www.example.com/segment.mp3", nil
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}
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