Add transcoding module comments

2 files changed, 37 insertions, 11 deletions

diff --git a/server/lib/video-transcoding-profiles.ts b/server/lib/video-transcoding-profiles.ts
index 91a5c65f2..03c26f236 100644
--- a/server/lib/video-transcoding-profiles.ts
+++ b/server/lib/video-transcoding-profiles.ts
@@ -1,11 +1,22 @@
+import { logger } from '@server/helpers/logger'
 import { getTargetBitrate } from '../../shared/models/videos'
 import { AvailableEncoders, buildStreamSuffix, EncoderOptionsBuilder } from '../helpers/ffmpeg-utils'
-import { ffprobePromise, getAudioStream, getMaxAudioBitrate, getVideoFileBitrate, getVideoStreamFromFile } from '../helpers/ffprobe-utils'
+import {
+  canDoQuickAudioTranscode,
+  ffprobePromise,
+  getAudioStream,
+  getMaxAudioBitrate,
+  getVideoFileBitrate,
+  getVideoStreamFromFile
+} from '../helpers/ffprobe-utils'
 import { VIDEO_TRANSCODING_FPS } from '../initializers/constants'
 
-// ---------------------------------------------------------------------------
-// Available encoders profiles
-// ---------------------------------------------------------------------------
+/**
+ *
+ * Available encoders and profiles for the transcoding jobs
+ * These functions are used by ffmpeg-utils that will get the encoders and options depending on the chosen profile
+ *
+ */
 
 // Resources:
 //  * https://slhck.info/video/2017/03/01/rate-control.html
@@ -27,7 +38,8 @@ const defaultX264VODOptionsBuilder: EncoderOptionsBuilder = async ({ input, reso
 
   return {
     outputOptions: [
-      `-maxrate ${targetBitrate}`, `-bufsize ${targetBitrate * 2}`
+      `-maxrate ${targetBitrate}`,
+      `-bufsize ${targetBitrate * 2}`
     ]
   }
 }
@@ -45,7 +57,14 @@ const defaultX264LiveOptionsBuilder: EncoderOptionsBuilder = async ({ resolution
 }
 
 const defaultAACOptionsBuilder: EncoderOptionsBuilder = async ({ input, streamNum }) => {
-  const parsedAudio = await getAudioStream(input)
+  const probe = await ffprobePromise(input)
+
+  if (await canDoQuickAudioTranscode(input, probe)) {
+    logger.debug('Copy audio stream %s by AAC encoder.', input)
+    return { copy: true, outputOptions: [] }
+  }
+
+  const parsedAudio = await getAudioStream(input, probe)
 
   // We try to reduce the ceiling bitrate by making rough matches of bitrates
   // Of course this is far from perfect, but it might save some space in the end
@@ -54,11 +73,13 @@ const defaultAACOptionsBuilder: EncoderOptionsBuilder = async ({ input, streamNu
 
   const bitrate = getMaxAudioBitrate(audioCodecName, parsedAudio.bitrate)
 
+  logger.debug('Calculating audio bitrate of %s by AAC encoder.', input, { bitrate: parsedAudio.bitrate, audioCodecName })
+
   if (bitrate !== undefined && bitrate !== -1) {
     return { outputOptions: [ buildStreamSuffix('-b:a', streamNum), bitrate + 'k' ] }
   }
 
-  return { copy: true, outputOptions: [] }
+  return { outputOptions: [ ] }
 }
 
 const defaultLibFDKAACVODOptionsBuilder: EncoderOptionsBuilder = ({ streamNum }) => {
diff --git a/server/lib/video-transcoding.ts b/server/lib/video-transcoding.ts
index aaad219dd..e022f2a68 100644
--- a/server/lib/video-transcoding.ts
+++ b/server/lib/video-transcoding.ts
@@ -16,8 +16,13 @@ import { generateVideoStreamingPlaylistName, getVideoFilename, getVideoFilePath
 import { availableEncoders } from './video-transcoding-profiles'
 
 /**
- * Optimize the original video file and replace it. The resolution is not changed.
+ *
+ * Functions that run transcoding functions, update the database, cleanup files, create torrent files...
+ * Mainly called by the job queue
+ *
  */
+
+// Optimize the original video file and replace it. The resolution is not changed.
 async function optimizeOriginalVideofile (video: MVideoWithFile, inputVideoFileArg?: MVideoFile) {
   const transcodeDirectory = CONFIG.STORAGE.TMP_DIR
   const newExtname = '.mp4'
@@ -62,9 +67,7 @@ async function optimizeOriginalVideofile (video: MVideoWithFile, inputVideoFileA
   }
 }
 
-/**
- * Transcode the original video file to a lower resolution.
- */
+// Transcode the original video file to a lower resolution.
 async function transcodeNewResolution (video: MVideoWithFile, resolution: VideoResolution, isPortrait: boolean) {
   const transcodeDirectory = CONFIG.STORAGE.TMP_DIR
   const extname = '.mp4'
@@ -110,6 +113,7 @@ async function transcodeNewResolution (video: MVideoWithFile, resolution: VideoR
   return onVideoFileTranscoding(video, newVideoFile, videoTranscodedPath, videoOutputPath)
 }
 
+// Merge an image with an audio file to create a video
 async function mergeAudioVideofile (video: MVideoWithAllFiles, resolution: VideoResolution) {
   const transcodeDirectory = CONFIG.STORAGE.TMP_DIR
   const newExtname = '.mp4'
@@ -159,6 +163,7 @@ async function mergeAudioVideofile (video: MVideoWithAllFiles, resolution: Video
   return onVideoFileTranscoding(video, inputVideoFile, videoTranscodedPath, videoOutputPath)
 }
 
+// Generate an HLS playlist from an input file, and update the master playlist
 async function generateHlsPlaylist (options: {
   video: MVideoWithFile
   videoInputPath: string