clipper/backend/media/media_set.go

132 lines
3.3 KiB
Go

package media
import (
"encoding/binary"
"encoding/json"
"errors"
"fmt"
"io"
"log"
"os"
"time"
)
const SizeOfInt16 = 2
type Audio struct {
Bytes int64 `json:"bytes"`
Channels int `json:"channels"`
// ApproxFrames is used during initial processing when a precise frame count
// cannot be determined. Prefer Frames in all other cases.
ApproxFrames int64 `json:"approx_frames"`
Frames int64 `json:"frames"`
SampleRate int `json:"sample_rate"`
}
type Video struct {
Bytes int64 `json:"bytes"`
Duration time.Duration `json:"duration"`
// not sure if this are needed any more?
ThumbnailWidth int `json:"thumbnail_width"`
ThumbnailHeight int `json:"thumbnail_height"`
}
// MediaSet represents the media and metadata associated with a single media
// resource (for example, a YouTube video).
type MediaSet struct {
Audio Audio `json:"audio"`
Video Video `json:"video"`
ID string `json:"id"`
exists bool
}
// New builds a new MediaSet with the given ID.
func NewMediaSet(id string) *MediaSet {
return &MediaSet{ID: id}
}
// TODO: pass io.Readers/Writers instead of strings.
func (m *MediaSet) RawAudioPath() string { return fmt.Sprintf("cache/%s.raw", m.ID) }
func (m *MediaSet) EncodedAudioPath() string { return fmt.Sprintf("cache/%s.m4a", m.ID) }
func (m *MediaSet) VideoPath() string { return fmt.Sprintf("cache/%s.mp4", m.ID) }
func (m *MediaSet) ThumbnailPath() string { return fmt.Sprintf("cache/%s.jpg", m.ID) }
func (m *MediaSet) MetadataPath() string { return fmt.Sprintf("cache/%s.json", m.ID) }
func (m *MediaSet) Exists() bool {
if m.ID == "" {
return false
}
if m.exists {
return true
}
if _, err := os.Stat(m.MetadataPath()); err == nil {
m.exists = true
return true
}
return false
}
func (m *MediaSet) Load() error {
if m.ID == "" {
return errors.New("error opening mediaset with blank ID")
}
metadataFile, err := os.Open(m.MetadataPath())
if err != nil {
return fmt.Errorf("error opening metadata file: %v", err)
}
defer func() { _ = metadataFile.Close() }()
if err := json.NewDecoder(metadataFile).Decode(m); err != nil {
return fmt.Errorf("error decoding metadata: %v", err)
}
return nil
}
func (m *MediaSet) Peaks(start, end int64, numBins int) ([][]int16, error) {
if !m.Exists() {
return nil, errors.New("cannot compute peaks for non-existent MediaSet")
}
var err error
fptr, err := os.Open(m.RawAudioPath())
if err != nil {
return nil, fmt.Errorf("audio open error: %v", err)
}
defer fptr.Close()
startByte := start * int64(m.Audio.Channels) * SizeOfInt16
if _, err = fptr.Seek(startByte, io.SeekStart); err != nil {
return nil, fmt.Errorf("audio seek error: %v", err)
}
numFrames := end - start
framesPerBin := numFrames / int64(numBins)
peaks := make([][]int16, m.Audio.Channels)
for i := 0; i < m.Audio.Channels; i++ {
peaks[i] = make([]int16, numBins)
}
samples := make([]int16, framesPerBin*int64(m.Audio.Channels))
for binNum := 0; binNum < numBins; binNum++ {
if err := binary.Read(fptr, binary.LittleEndian, samples); err != nil {
return nil, fmt.Errorf("error reading samples: %v", err)
}
for i, samp := range samples {
if samp < 0 {
samp = -samp
}
chanIndex := i % m.Audio.Channels
if samp > peaks[chanIndex][binNum] {
peaks[chanIndex][binNum] = samp
}
}
}
log.Println("finished generating peaks")
return peaks, nil
}