clipper/backend/media/get_audio.go

package media

import (
	"bytes"
	"context"
	"encoding/binary"
	"fmt"
	"io"
	"math"
	"os/exec"
	"strconv"
	"sync"

	"git.netflux.io/rob/clipper/config"
	"git.netflux.io/rob/clipper/generated/store"
	"go.uber.org/zap"
)

type GetPeaksProgress struct {
	PercentComplete float32
	Peaks           []int16
	URL             string
}

type GetPeaksProgressReader interface {
	Next() (GetPeaksProgress, error)
	Close(string) error
}

// audioGetter manages getting and processing audio from Youtube.
type audioGetter struct {
	store     Store
	youtube   YoutubeClient
	fileStore FileStore
	config    config.Config
	logger    *zap.SugaredLogger
}

// newAudioGetter returns a new audioGetter.
func newAudioGetter(store Store, youtube YoutubeClient, fileStore FileStore, config config.Config, logger *zap.SugaredLogger) *audioGetter {
	return &audioGetter{
		store:     store,
		youtube:   youtube,
		fileStore: fileStore,
		config:    config,
		logger:    logger,
	}
}

// GetAudio gets the audio, processes it and uploads it to a file store. It
// returns a GetAudioProgressReader that can be used to poll progress reports
// and audio peaks.
//
// TODO: accept domain object instead
func (g *audioGetter) GetAudio(ctx context.Context, mediaSet store.MediaSet, numBins int) (GetPeaksProgressReader, error) {
	video, err := g.youtube.GetVideoContext(ctx, mediaSet.YoutubeID)
	if err != nil {
		return nil, fmt.Errorf("error fetching video: %v", err)
	}

	format := video.Formats.FindByItag(int(mediaSet.AudioYoutubeItag))
	if format == nil {
		return nil, fmt.Errorf("error finding itag: %v", err)
	}

	stream, _, err := g.youtube.GetStreamContext(ctx, video, format)
	if err != nil {
		return nil, fmt.Errorf("error fetching stream: %v", err)
	}

	audioProgressReader, err := newGetPeaksProgressReader(mediaSet.AudioFramesApprox, int(mediaSet.AudioChannels), numBins)
	if err != nil {
		return nil, fmt.Errorf("error building progress reader: %v", err)
	}

	s := &audioGetterState{
		audioGetter:            g,
		getPeaksProgressReader: audioProgressReader,
	}
	go s.getAudio(ctx, stream, mediaSet)

	return s, nil
}

// audioGetterState represents the state of an individual audio fetch.
type audioGetterState struct {
	*audioGetter
	*getPeaksProgressReader
}

func (s *audioGetterState) getAudio(ctx context.Context, r io.ReadCloser, mediaSet store.MediaSet) {
	streamWithProgress := newLogProgressReader(r, "audio", mediaSet.AudioContentLength, s.logger)
	pr, pw := io.Pipe()
	teeReader := io.TeeReader(streamWithProgress, pw)

	var stdErr bytes.Buffer
	cmd := exec.CommandContext(ctx, "ffmpeg", "-hide_banner", "-loglevel", "error", "-i", "-", "-f", rawAudioFormat, "-ar", strconv.Itoa(rawAudioSampleRate), "-acodec", rawAudioCodec, "-")
	cmd.Stdin = teeReader
	cmd.Stderr = &stdErr
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		s.CloseWithError(fmt.Errorf("error getting stdout: %v", err))
		return
	}
	if err = cmd.Start(); err != nil {
		s.CloseWithError(fmt.Errorf("error starting command: %v, output: %s", err, stdErr.String()))
		return
	}

	var presignedAudioURL string
	var wg sync.WaitGroup
	wg.Add(2)

	// Upload the encoded audio.
	// TODO: fix error shadowing in these two goroutines.
	go func() {
		defer wg.Done()

		// TODO: use mediaSet func to fetch key
		key := fmt.Sprintf("media_sets/%s/audio.opus", mediaSet.ID)

		_, encErr := s.fileStore.PutObject(ctx, key, pr, "audio/opus")
		if encErr != nil {
			s.CloseWithError(fmt.Errorf("error uploading encoded audio: %v", encErr))
			return
		}

		presignedAudioURL, err = s.fileStore.GetURL(ctx, key)
		if err != nil {
			s.CloseWithError(fmt.Errorf("error generating presigned URL: %v", err))
		}

		if _, err = s.store.SetEncodedAudioUploaded(ctx, store.SetEncodedAudioUploadedParams{
			ID:                mediaSet.ID,
			AudioEncodedS3Key: sqlString(key),
		}); err != nil {
			s.CloseWithError(fmt.Errorf("error setting encoded audio uploaded: %v", err))
		}
	}()

	// Upload the raw audio.
	go func() {
		defer wg.Done()

		// TODO: use mediaSet func to fetch key
		key := fmt.Sprintf("media_sets/%s/audio.raw", mediaSet.ID)

		teeReader := io.TeeReader(stdout, s)
		bytesUploaded, rawErr := s.fileStore.PutObject(ctx, key, teeReader, rawAudioMimeType)
		if rawErr != nil {
			s.CloseWithError(fmt.Errorf("error uploading raw audio: %v", rawErr))
			return
		}

		if _, err = s.store.SetRawAudioUploaded(ctx, store.SetRawAudioUploadedParams{
			ID:            mediaSet.ID,
			AudioRawS3Key: sqlString(key),
			AudioFrames:   sqlInt64(bytesUploaded / SizeOfInt16 / int64(mediaSet.AudioChannels)),
		}); err != nil {
			s.CloseWithError(fmt.Errorf("error setting raw audio uploaded: %v", err))
		}
	}()

	if err = cmd.Wait(); err != nil {
		// TODO: cancel other goroutines (e.g. video fetch) if an error occurs here.
		s.CloseWithError(fmt.Errorf("error waiting for command: %v, output: %s", err, stdErr.String()))
		return
	}

	// Close the pipe sending encoded audio to be uploaded, this ensures the
	// uploader reading from the pipe will receive io.EOF and complete
	// successfully.
	pw.Close()

	// Wait for the uploaders to complete.
	wg.Wait()

	// Finally, close the progress reader so that the subsequent call to Next()
	// returns the presigned URL and io.EOF.
	s.Close(presignedAudioURL)
}

// getPeaksProgressReader 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 getPeaksProgressReader struct {
	framesExpected int64
	channels       int
	framesPerBin   int

	samples         []int16
	currPeaks       []int16
	currCount       int
	framesProcessed int64
	url             string
	progress        chan GetPeaksProgress
	errorChan       chan error
}

func newGetPeaksProgressReader(framesExpected int64, channels, numBins int) (*getPeaksProgressReader, error) {
	if framesExpected <= 0 || channels <= 0 || numBins <= 0 {
		return nil, fmt.Errorf("error creating audio progress reader (framesExpected = %d, channels = %d, numBins = %d)", framesExpected, channels, numBins)
	}

	return &getPeaksProgressReader{
		channels:       channels,
		framesExpected: framesExpected,
		framesPerBin:   int(math.Ceil(float64(framesExpected) / float64(numBins))),
		samples:        make([]int16, 8_192),
		currPeaks:      make([]int16, channels),
		progress:       make(chan GetPeaksProgress),
		errorChan:      make(chan error, 1),
	}, nil
}

func (w *getPeaksProgressReader) CloseWithError(err error) {
	w.errorChan <- err
}

// Close cloes the reader and returns the provided URL to the calling code.
func (w *getPeaksProgressReader) Close(url string) error {
	w.url = url
	close(w.progress)
	return nil
}

func (w *getPeaksProgressReader) Next() (GetPeaksProgress, error) {
	for {
		select {
		case progress, ok := <-w.progress:
			if !ok {
				return GetPeaksProgress{Peaks: w.currPeaks, PercentComplete: w.percentComplete(), URL: w.url}, io.EOF
			}
			return progress, nil
		case err := <-w.errorChan:
			return GetPeaksProgress{}, fmt.Errorf("error waiting for progress: %v", err)
		}
	}
}

func (w *getPeaksProgressReader) 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()
		}
	}

	w.framesProcessed += int64(len(samples) / w.channels)

	return len(p), nil
}

func (w *getPeaksProgressReader) percentComplete() float32 {
	return (float32(w.framesProcessed) / float32(w.framesExpected)) * 100.0
}

func (w *getPeaksProgressReader) nextBin() {
	var progress GetPeaksProgress
	progress.Peaks = append(progress.Peaks, w.currPeaks...)
	progress.PercentComplete = w.percentComplete()

	w.progress <- progress

	w.currCount = 0
	for i := 0; i < len(w.currPeaks); i++ {
		w.currPeaks[i] = 0
	}
}