Set bitrate limits for transcoding (fixes #638) (#1135)

* Set bitrate limits for transcoding (fixes #638)

* added optimization script and test, changed stuff

* fix test, improve docs

* re-add optimize-old-videos script

* added documentation

* Don't optimize videos without valid UUID, or redundancy videos

* move getUUIDFromFilename

* fix tests?

* update torrent and file size, some more fixes/improvements

* use higher bitrate for high fps video, adjust bitrates

* add test video

* don't throw error if resolution is undefined

* generate test fixture on the fly

* use random noise video for bitrate test, add promise

* shorten test video to avoid timeout

* use existing function to optimize video

* various fixes

* increase test timeout

* limit test fixture size, add link

* test fixes

* add await

* more test fixes, add -b:v parameter

* replace ffmpeg wiki link

* fix ffmpeg params

* fix unit test

* add test fixture to .gitgnore

* add video transcoding fps model

* add missing file

1 files changed, 19 insertions, 2 deletions

diff --git a/server/helpers/ffmpeg-utils.ts b/server/helpers/ffmpeg-utils.ts
index 22bc25476..8e4471173 100644
--- a/server/helpers/ffmpeg-utils.ts
+++ b/server/helpers/ffmpeg-utils.ts
@@ -1,6 +1,6 @@
 import * as ffmpeg from 'fluent-ffmpeg'
 import { join } from 'path'
-import { VideoResolution } from '../../shared/models/videos'
+import { VideoResolution, getTargetBitrate } from '../../shared/models/videos'
 import { CONFIG, FFMPEG_NICE, VIDEO_TRANSCODING_FPS } from '../initializers'
 import { processImage } from './image-utils'
 import { logger } from './logger'
@@ -55,6 +55,16 @@ async function getVideoFileFPS (path: string) {
   return 0
 }
 
+async function getVideoFileBitrate (path: string) {
+  return new Promise<number>((res, rej) => {
+    ffmpeg.ffprobe(path, (err, metadata) => {
+      if (err) return rej(err)
+
+      return res(metadata.format.bit_rate)
+    })
+  })
+}
+
 function getDurationFromVideoFile (path: string) {
   return new Promise<number>((res, rej) => {
     ffmpeg.ffprobe(path, (err, metadata) => {
@@ -138,6 +148,12 @@ function transcode (options: TranscodeOptions) {
       command = command.withFPS(fps)
     }
 
+    // Constrained Encoding (VBV)
+    // https://slhck.info/video/2017/03/01/rate-control.html
+    // https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
+    const targetBitrate = getTargetBitrate(options.resolution, fps, VIDEO_TRANSCODING_FPS)
+    command.outputOptions([`-b:v ${ targetBitrate }`, `-maxrate ${ targetBitrate }`, `-bufsize ${ targetBitrate * 2 }`])
+
     command
       .on('error', (err, stdout, stderr) => {
         logger.error('Error in transcoding job.', { stdout, stderr })
@@ -157,7 +173,8 @@ export {
   transcode,
   getVideoFileFPS,
   computeResolutionsToTranscode,
-  audio
+  audio,
+  getVideoFileBitrate
 }
 
 // ---------------------------------------------------------------------------