From 7d91340582934e51c4ce831b18e28678f038e210 Mon Sep 17 00:00:00 2001
From: Rob Watson <rob@netflux.io>
Date: Tue, 19 Oct 2021 17:37:54 +0200
Subject: [PATCH] Reduce audio and video bitrates

---
 backend/youtube/helpers.go | 17 +++++------------
 backend/youtube/youtube.go | 12 +++++++-----
 2 files changed, 12 insertions(+), 17 deletions(-)

diff --git a/backend/youtube/helpers.go b/backend/youtube/helpers.go
index f206152..810b851 100644
--- a/backend/youtube/helpers.go
+++ b/backend/youtube/helpers.go
@@ -33,10 +33,9 @@ func FormatDebugString(format *youtubev2.Format, includeURL bool) string {
 }
 
 // SortAudio returns the provided formats ordered in descending preferred
-// order. The ideal candidate is 44.1kHz stereo audio in a webm container, with
-// the highest available bitrate.
+// order. The ideal candidate is opus-encoded stereo audio in a webm container,
+// with the lowest available bitrate.
 func SortAudio(inFormats youtubev2.FormatList) youtubev2.FormatList {
-	// TODO: sort in-place.
 	var formats youtubev2.FormatList
 	for _, format := range inFormats {
 		if format.FPS == 0 && format.AudioChannels > 0 {
@@ -50,12 +49,7 @@ func SortAudio(inFormats youtubev2.FormatList) youtubev2.FormatList {
 			isStereoI := formats[i].AudioChannels == 2
 			isStereoJ := formats[j].AudioChannels == 2
 			if isStereoI && isStereoJ {
-				is48kI := formats[i].AudioSampleRate == "48000"
-				is48kJ := formats[j].AudioSampleRate == "48000"
-				if is48kI && is48kJ {
-					return formats[i].Bitrate > formats[j].Bitrate
-				}
-				return is48kI
+				return formats[i].ContentLength < formats[j].ContentLength
 			}
 			return isStereoI
 		}
@@ -69,10 +63,9 @@ func SortAudio(inFormats youtubev2.FormatList) youtubev2.FormatList {
 // bitrate, with audio channels (needed to allow synced playback on the
 // website).
 func SortVideo(inFormats youtubev2.FormatList) youtubev2.FormatList {
-	// TODO: sort in-place.
 	var formats youtubev2.FormatList
 	for _, format := range inFormats {
-		if format.FPS > 0 && format.ContentLength > 0 && format.AudioChannels > 0 {
+		if format.FPS > 0 && format.ContentLength > 0 {
 			formats = append(formats, format)
 		}
 	}
@@ -80,7 +73,7 @@ func SortVideo(inFormats youtubev2.FormatList) youtubev2.FormatList {
 		isMP4I := strings.Contains(formats[i].MimeType, "mp4")
 		isMP4J := strings.Contains(formats[j].MimeType, "mp4")
 		if isMP4I && isMP4J {
-			return formats[i].Bitrate < formats[j].Bitrate
+			return formats[i].ContentLength < formats[j].ContentLength
 		}
 		return isMP4I
 	})
diff --git a/backend/youtube/youtube.go b/backend/youtube/youtube.go
index 204bb7b..d15c886 100644
--- a/backend/youtube/youtube.go
+++ b/backend/youtube/youtube.go
@@ -88,7 +88,7 @@ func (d *Downloader) Download(ctx context.Context, videoID string) (*media.Media
 	}()
 	go func() {
 		defer close(videoResultChan)
-		video, videoErr := d.downloadVideo(ctx, video, mediaSet.VideoPath(), mediaSet.ThumbnailPath())
+		video, videoErr := d.downloadVideo(ctx, video, mediaSet.VideoPath())
 		result := videoResult{video, videoErr}
 		videoResultChan <- result
 		wg.Done()
@@ -138,6 +138,7 @@ func (d *Downloader) downloadAudio(ctx context.Context, video *youtubev2.Video,
 	if err != nil {
 		return nil, fmt.Errorf("error fetching audio stream: %v", err)
 	}
+	reader := progressReader{Reader: stream, label: "audio", exp: int(format.ContentLength)}
 
 	rawAudioFile, err := os.Create(rawOutPath)
 	if err != nil {
@@ -148,7 +149,7 @@ func (d *Downloader) downloadAudio(ctx context.Context, video *youtubev2.Video,
 	if err != nil {
 		return nil, fmt.Errorf("error creating encoded audio file: %v", err)
 	}
-	streamReader := io.TeeReader(stream, encodedAudioFile)
+	streamReader := io.TeeReader(&reader, encodedAudioFile)
 
 	var errOut bytes.Buffer
 	cmd := exec.CommandContext(ctx, "ffmpeg", "-i", "-", "-f", rawAudioFormat, "-ar", strconv.Itoa(rawAudioSampleRate), "-acodec", rawAudioCodec, "-")
@@ -191,6 +192,7 @@ func (d *Downloader) downloadAudio(ctx context.Context, video *youtubev2.Video,
 
 type progressReader struct {
 	io.Reader
+	label      string
 	total, exp int
 }
 
@@ -198,12 +200,12 @@ func (pw *progressReader) Read(p []byte) (int, error) {
 	n, err := pw.Reader.Read(p)
 	pw.total += n
 
-	log.Printf("[ProgressReader] Read %d of %d (%.02f%%) bytes from the provided reader", pw.total, pw.exp, (float32(pw.total)/float32(pw.exp))*100.0)
+	log.Printf("[ProgressReader] [%s] Read %d of %d (%.02f%%) bytes from the provided reader", pw.label, pw.total, pw.exp, (float32(pw.total)/float32(pw.exp))*100.0)
 
 	return n, err
 }
 
-func (d *Downloader) downloadVideo(ctx context.Context, video *youtubev2.Video, outPath string, thumbnailOutPath string) (*media.Video, error) {
+func (d *Downloader) downloadVideo(ctx context.Context, video *youtubev2.Video, outPath string) (*media.Video, error) {
 	if len(video.Formats) == 0 {
 		return nil, errors.New("error selecting audio format: no format available")
 	}
@@ -219,7 +221,7 @@ func (d *Downloader) downloadVideo(ctx context.Context, video *youtubev2.Video,
 	if err != nil {
 		return nil, fmt.Errorf("error fetching video stream: %v", err)
 	}
-	reader := progressReader{Reader: stream, exp: int(format.ContentLength)}
+	reader := progressReader{Reader: stream, label: "video", exp: int(format.ContentLength)}
 
 	videoFile, err := os.Create(outPath)
 	if err != nil {