server/helpers/ffmpeg-utils.ts

   1 import * as ffmpeg from 'fluent-ffmpeg'
   2 import { readFile, remove, writeFile } from 'fs-extra'
   3 import { dirname, join } from 'path'
   4 import { VideoFileMetadata } from '@shared/models/videos/video-file-metadata'
   5 import { getMaxBitrate, getTargetBitrate, VideoResolution } from '../../shared/models/videos'
   6 import { checkFFmpegEncoders } from '../initializers/checker-before-init'
   7 import { CONFIG } from '../initializers/config'
   8 import { FFMPEG_NICE, VIDEO_LIVE, VIDEO_TRANSCODING_FPS } from '../initializers/constants'
   9 import { processImage } from './image-utils'
  10 import { logger } from './logger'
  11
  12 /**
  13  * A toolbox to play with audio
  14  */
  15 namespace audio {
  16   export const get = (videoPath: string) => {
  17     // without position, ffprobe considers the last input only
  18     // we make it consider the first input only
  19     // if you pass a file path to pos, then ffprobe acts on that file directly
  20     return new Promise<{ absolutePath: string, audioStream?: any }>((res, rej) => {
  21
  22       function parseFfprobe (err: any, data: ffmpeg.FfprobeData) {
  23         if (err) return rej(err)
  24
  25         if ('streams' in data) {
  26           const audioStream = data.streams.find(stream => stream['codec_type'] === 'audio')
  27           if (audioStream) {
  28             return res({
  29               absolutePath: data.format.filename,
  30               audioStream
  31             })
  32           }
  33         }
  34
  35         return res({ absolutePath: data.format.filename })
  36       }
  37
  38       return ffmpeg.ffprobe(videoPath, parseFfprobe)
  39     })
  40   }
  41
  42   export namespace bitrate {
  43     const baseKbitrate = 384
  44
  45     const toBits = (kbits: number) => kbits * 8000
  46
  47     export const aac = (bitrate: number): number => {
  48       switch (true) {
  49         case bitrate > toBits(baseKbitrate):
  50           return baseKbitrate
  51
  52         default:
  53           return -1 // we interpret it as a signal to copy the audio stream as is
  54       }
  55     }
  56
  57     export const mp3 = (bitrate: number): number => {
  58       /*
  59       a 192kbit/sec mp3 doesn't hold as much information as a 192kbit/sec aac.
  60       That's why, when using aac, we can go to lower kbit/sec. The equivalences
  61       made here are not made to be accurate, especially with good mp3 encoders.
  62       */
  63       switch (true) {
  64         case bitrate <= toBits(192):
  65           return 128
  66
  67         case bitrate <= toBits(384):
  68           return 256
  69
  70         default:
  71           return baseKbitrate
  72       }
  73     }
  74   }
  75 }
  76
  77 function computeResolutionsToTranscode (videoFileResolution: number, type: 'vod' | 'live') {
  78   const configResolutions = type === 'vod'
  79     ? CONFIG.TRANSCODING.RESOLUTIONS
  80     : CONFIG.LIVE.TRANSCODING.RESOLUTIONS
  81
  82   const resolutionsEnabled: number[] = []
  83
  84   // Put in the order we want to proceed jobs
  85   const resolutions = [
  86     VideoResolution.H_NOVIDEO,
  87     VideoResolution.H_480P,
  88     VideoResolution.H_360P,
  89     VideoResolution.H_720P,
  90     VideoResolution.H_240P,
  91     VideoResolution.H_1080P,
  92     VideoResolution.H_4K
  93   ]
  94
  95   for (const resolution of resolutions) {
  96     if (configResolutions[resolution + 'p'] === true && videoFileResolution > resolution) {
  97       resolutionsEnabled.push(resolution)
  98     }
  99   }
 100
 101   return resolutionsEnabled
 102 }
 103
 104 async function getVideoStreamSize (path: string) {
 105   const videoStream = await getVideoStreamFromFile(path)
 106
 107   return videoStream === null
 108     ? { width: 0, height: 0 }
 109     : { width: videoStream.width, height: videoStream.height }
 110 }
 111
 112 async function getVideoStreamCodec (path: string) {
 113   const videoStream = await getVideoStreamFromFile(path)
 114
 115   if (!videoStream) return ''
 116
 117   const videoCodec = videoStream.codec_tag_string
 118
 119   const baseProfileMatrix = {
 120     High: '6400',
 121     Main: '4D40',
 122     Baseline: '42E0'
 123   }
 124
 125   let baseProfile = baseProfileMatrix[videoStream.profile]
 126   if (!baseProfile) {
 127     logger.warn('Cannot get video profile codec of %s.', path, { videoStream })
 128     baseProfile = baseProfileMatrix['High'] // Fallback
 129   }
 130
 131   let level = videoStream.level.toString(16)
 132   if (level.length === 1) level = `0${level}`
 133
 134   return `${videoCodec}.${baseProfile}${level}`
 135 }
 136
 137 async function getAudioStreamCodec (path: string) {
 138   const { audioStream } = await audio.get(path)
 139
 140   if (!audioStream) return ''
 141
 142   const audioCodec = audioStream.codec_name
 143   if (audioCodec === 'aac') return 'mp4a.40.2'
 144
 145   logger.warn('Cannot get audio codec of %s.', path, { audioStream })
 146
 147   return 'mp4a.40.2' // Fallback
 148 }
 149
 150 async function getVideoFileResolution (path: string) {
 151   const size = await getVideoStreamSize(path)
 152
 153   return {
 154     videoFileResolution: Math.min(size.height, size.width),
 155     isPortraitMode: size.height > size.width
 156   }
 157 }
 158
 159 async function getVideoFileFPS (path: string) {
 160   const videoStream = await getVideoStreamFromFile(path)
 161   if (videoStream === null) return 0
 162
 163   for (const key of [ 'avg_frame_rate', 'r_frame_rate' ]) {
 164     const valuesText: string = videoStream[key]
 165     if (!valuesText) continue
 166
 167     const [ frames, seconds ] = valuesText.split('/')
 168     if (!frames || !seconds) continue
 169
 170     const result = parseInt(frames, 10) / parseInt(seconds, 10)
 171     if (result > 0) return Math.round(result)
 172   }
 173
 174   return 0
 175 }
 176
 177 async function getMetadataFromFile <T> (path: string, cb = metadata => metadata) {
 178   return new Promise<T>((res, rej) => {
 179     ffmpeg.ffprobe(path, (err, metadata) => {
 180       if (err) return rej(err)
 181
 182       return res(cb(new VideoFileMetadata(metadata)))
 183     })
 184   })
 185 }
 186
 187 async function getVideoFileBitrate (path: string) {
 188   return getMetadataFromFile<number>(path, metadata => metadata.format.bit_rate)
 189 }
 190
 191 function getDurationFromVideoFile (path: string) {
 192   return getMetadataFromFile<number>(path, metadata => Math.floor(metadata.format.duration))
 193 }
 194
 195 function getVideoStreamFromFile (path: string) {
 196   return getMetadataFromFile<any>(path, metadata => metadata.streams.find(s => s.codec_type === 'video') || null)
 197 }
 198
 199 async function generateImageFromVideoFile (fromPath: string, folder: string, imageName: string, size: { width: number, height: number }) {
 200   const pendingImageName = 'pending-' + imageName
 201
 202   const options = {
 203     filename: pendingImageName,
 204     count: 1,
 205     folder
 206   }
 207
 208   const pendingImagePath = join(folder, pendingImageName)
 209
 210   try {
 211     await new Promise<string>((res, rej) => {
 212       ffmpeg(fromPath, { niceness: FFMPEG_NICE.THUMBNAIL })
 213         .on('error', rej)
 214         .on('end', () => res(imageName))
 215         .thumbnail(options)
 216     })
 217
 218     const destination = join(folder, imageName)
 219     await processImage(pendingImagePath, destination, size)
 220   } catch (err) {
 221     logger.error('Cannot generate image from video %s.', fromPath, { err })
 222
 223     try {
 224       await remove(pendingImagePath)
 225     } catch (err) {
 226       logger.debug('Cannot remove pending image path after generation error.', { err })
 227     }
 228   }
 229 }
 230
 231 type TranscodeOptionsType = 'hls' | 'quick-transcode' | 'video' | 'merge-audio' | 'only-audio'
 232
 233 interface BaseTranscodeOptions {
 234   type: TranscodeOptionsType
 235   inputPath: string
 236   outputPath: string
 237   resolution: VideoResolution
 238   isPortraitMode?: boolean
 239 }
 240
 241 interface HLSTranscodeOptions extends BaseTranscodeOptions {
 242   type: 'hls'
 243   copyCodecs: boolean
 244   hlsPlaylist: {
 245     videoFilename: string
 246   }
 247 }
 248
 249 interface QuickTranscodeOptions extends BaseTranscodeOptions {
 250   type: 'quick-transcode'
 251 }
 252
 253 interface VideoTranscodeOptions extends BaseTranscodeOptions {
 254   type: 'video'
 255 }
 256
 257 interface MergeAudioTranscodeOptions extends BaseTranscodeOptions {
 258   type: 'merge-audio'
 259   audioPath: string
 260 }
 261
 262 interface OnlyAudioTranscodeOptions extends BaseTranscodeOptions {
 263   type: 'only-audio'
 264 }
 265
 266 type TranscodeOptions =
 267   HLSTranscodeOptions
 268   | VideoTranscodeOptions
 269   | MergeAudioTranscodeOptions
 270   | OnlyAudioTranscodeOptions
 271   | QuickTranscodeOptions
 272
 273 function transcode (options: TranscodeOptions) {
 274   return new Promise<void>(async (res, rej) => {
 275     try {
 276       let command = getFFmpeg(options.inputPath)
 277         .output(options.outputPath)
 278
 279       if (options.type === 'quick-transcode') {
 280         command = buildQuickTranscodeCommand(command)
 281       } else if (options.type === 'hls') {
 282         command = await buildHLSVODCommand(command, options)
 283       } else if (options.type === 'merge-audio') {
 284         command = await buildAudioMergeCommand(command, options)
 285       } else if (options.type === 'only-audio') {
 286         command = buildOnlyAudioCommand(command, options)
 287       } else {
 288         command = await buildx264Command(command, options)
 289       }
 290
 291       command
 292         .on('error', (err, stdout, stderr) => {
 293           logger.error('Error in transcoding job.', { stdout, stderr })
 294           return rej(err)
 295         })
 296         .on('end', () => {
 297           return fixHLSPlaylistIfNeeded(options)
 298             .then(() => res())
 299             .catch(err => rej(err))
 300         })
 301         .run()
 302     } catch (err) {
 303       return rej(err)
 304     }
 305   })
 306 }
 307
 308 async function canDoQuickTranscode (path: string): Promise<boolean> {
 309   // NOTE: This could be optimized by running ffprobe only once (but it runs fast anyway)
 310   const videoStream = await getVideoStreamFromFile(path)
 311   const parsedAudio = await audio.get(path)
 312   const fps = await getVideoFileFPS(path)
 313   const bitRate = await getVideoFileBitrate(path)
 314   const resolution = await getVideoFileResolution(path)
 315
 316   // check video params
 317   if (videoStream == null) return false
 318   if (videoStream['codec_name'] !== 'h264') return false
 319   if (videoStream['pix_fmt'] !== 'yuv420p') return false
 320   if (fps < VIDEO_TRANSCODING_FPS.MIN || fps > VIDEO_TRANSCODING_FPS.MAX) return false
 321   if (bitRate > getMaxBitrate(resolution.videoFileResolution, fps, VIDEO_TRANSCODING_FPS)) return false
 322
 323   // check audio params (if audio stream exists)
 324   if (parsedAudio.audioStream) {
 325     if (parsedAudio.audioStream['codec_name'] !== 'aac') return false
 326
 327     const maxAudioBitrate = audio.bitrate['aac'](parsedAudio.audioStream['bit_rate'])
 328     if (maxAudioBitrate !== -1 && parsedAudio.audioStream['bit_rate'] > maxAudioBitrate) return false
 329   }
 330
 331   return true
 332 }
 333
 334 function getClosestFramerateStandard (fps: number, type: 'HD_STANDARD' | 'STANDARD'): number {
 335   return VIDEO_TRANSCODING_FPS[type].slice(0)
 336                                     .sort((a, b) => fps % a - fps % b)[0]
 337 }
 338
 339 function convertWebPToJPG (path: string, destination: string): Promise<void> {
 340   return new Promise<void>(async (res, rej) => {
 341     try {
 342       const command = ffmpeg(path).output(destination)
 343
 344       command.on('error', (err, stdout, stderr) => {
 345         logger.error('Error in ffmpeg webp convert process.', { stdout, stderr })
 346         return rej(err)
 347       })
 348       .on('end', () => res())
 349       .run()
 350     } catch (err) {
 351       return rej(err)
 352     }
 353   })
 354 }
 355
 356 function runLiveTranscoding (rtmpUrl: string, outPath: string, resolutions: number[], deleteSegments: boolean) {
 357   const command = getFFmpeg(rtmpUrl)
 358   command.inputOption('-fflags nobuffer')
 359
 360   const varStreamMap: string[] = []
 361
 362   command.complexFilter([
 363     {
 364       inputs: '[v:0]',
 365       filter: 'split',
 366       options: resolutions.length,
 367       outputs: resolutions.map(r => `vtemp${r}`)
 368     },
 369
 370     ...resolutions.map(r => ({
 371       inputs: `vtemp${r}`,
 372       filter: 'scale',
 373       options: `w=-2:h=${r}`,
 374       outputs: `vout${r}`
 375     }))
 376   ])
 377
 378   const liveFPS = VIDEO_TRANSCODING_FPS.AVERAGE
 379
 380   command.withFps(liveFPS)
 381
 382   command.outputOption('-b_strategy 1')
 383   command.outputOption('-bf 16')
 384   command.outputOption('-preset superfast')
 385   command.outputOption('-level 3.1')
 386   command.outputOption('-map_metadata -1')
 387   command.outputOption('-pix_fmt yuv420p')
 388   command.outputOption('-max_muxing_queue_size 1024')
 389
 390   for (let i = 0; i < resolutions.length; i++) {
 391     const resolution = resolutions[i]
 392
 393     command.outputOption(`-map [vout${resolution}]`)
 394     command.outputOption(`-c:v:${i} libx264`)
 395     command.outputOption(`-b:v:${i} ${getTargetBitrate(resolution, liveFPS, VIDEO_TRANSCODING_FPS)}`)
 396
 397     command.outputOption(`-map a:0`)
 398     command.outputOption(`-c:a:${i} aac`)
 399
 400     varStreamMap.push(`v:${i},a:${i}`)
 401   }
 402
 403   addDefaultLiveHLSParams(command, outPath, deleteSegments)
 404
 405   command.outputOption('-var_stream_map', varStreamMap.join(' '))
 406
 407   command.run()
 408
 409   return command
 410 }
 411
 412 function runLiveMuxing (rtmpUrl: string, outPath: string, deleteSegments: boolean) {
 413   const command = getFFmpeg(rtmpUrl)
 414   command.inputOption('-fflags nobuffer')
 415
 416   command.outputOption('-c:v copy')
 417   command.outputOption('-c:a copy')
 418   command.outputOption('-map 0:a?')
 419   command.outputOption('-map 0:v?')
 420
 421   addDefaultLiveHLSParams(command, outPath, deleteSegments)
 422
 423   command.run()
 424
 425   return command
 426 }
 427
 428 async function hlsPlaylistToFragmentedMP4 (hlsDirectory: string, segmentFiles: string[], outputPath: string) {
 429   const concatFile = 'concat.txt'
 430   const concatFilePath = join(hlsDirectory, concatFile)
 431   const content = segmentFiles.map(f => 'file ' + f)
 432                               .join('\n')
 433
 434   await writeFile(concatFilePath, content + '\n')
 435
 436   const command = getFFmpeg(concatFilePath)
 437   command.inputOption('-safe 0')
 438   command.inputOption('-f concat')
 439
 440   command.outputOption('-c copy')
 441   command.output(outputPath)
 442
 443   command.run()
 444
 445   function cleaner () {
 446     remove(concatFile)
 447     .catch(err => logger.error('Cannot remove concat file in %s.', hlsDirectory, { err }))
 448   }
 449
 450   return new Promise<string>((res, rej) => {
 451     command.on('error', err => {
 452       cleaner()
 453
 454       rej(err)
 455     })
 456
 457     command.on('end', () => {
 458       cleaner()
 459
 460       res()
 461     })
 462   })
 463 }
 464
 465 // ---------------------------------------------------------------------------
 466
 467 export {
 468   getVideoStreamCodec,
 469   getAudioStreamCodec,
 470   runLiveMuxing,
 471   convertWebPToJPG,
 472   getVideoStreamSize,
 473   getVideoFileResolution,
 474   getMetadataFromFile,
 475   getDurationFromVideoFile,
 476   runLiveTranscoding,
 477   generateImageFromVideoFile,
 478   TranscodeOptions,
 479   TranscodeOptionsType,
 480   transcode,
 481   getVideoFileFPS,
 482   computeResolutionsToTranscode,
 483   audio,
 484   hlsPlaylistToFragmentedMP4,
 485   getVideoFileBitrate,
 486   canDoQuickTranscode
 487 }
 488
 489 // ---------------------------------------------------------------------------
 490
 491 function addDefaultX264Params (command: ffmpeg.FfmpegCommand) {
 492   command.outputOption('-level 3.1') // 3.1 is the minimal resource allocation for our highest supported resolution
 493          .outputOption('-b_strategy 1') // NOTE: b-strategy 1 - heuristic algorithm, 16 is optimal B-frames for it
 494          .outputOption('-bf 16') // NOTE: Why 16: https://github.com/Chocobozzz/PeerTube/pull/774. b-strategy 2 -> B-frames<16
 495          .outputOption('-pix_fmt yuv420p') // allows import of source material with incompatible pixel formats (e.g. MJPEG video)
 496          .outputOption('-map_metadata -1') // strip all metadata
 497 }
 498
 499 function addDefaultLiveHLSParams (command: ffmpeg.FfmpegCommand, outPath: string, deleteSegments: boolean) {
 500   command.outputOption('-hls_time ' + VIDEO_LIVE.SEGMENT_TIME)
 501   command.outputOption('-hls_list_size ' + VIDEO_LIVE.SEGMENTS_LIST_SIZE)
 502
 503   if (deleteSegments === true) {
 504     command.outputOption('-hls_flags delete_segments')
 505   }
 506
 507   command.outputOption(`-hls_segment_filename ${join(outPath, '%v-%d.ts')}`)
 508   command.outputOption('-master_pl_name master.m3u8')
 509   command.outputOption(`-f hls`)
 510
 511   command.output(join(outPath, '%v.m3u8'))
 512 }
 513
 514 async function buildx264Command (command: ffmpeg.FfmpegCommand, options: TranscodeOptions) {
 515   let fps = await getVideoFileFPS(options.inputPath)
 516   if (
 517     // On small/medium resolutions, limit FPS
 518     options.resolution !== undefined &&
 519     options.resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
 520     fps > VIDEO_TRANSCODING_FPS.AVERAGE
 521   ) {
 522     // Get closest standard framerate by modulo: downsampling has to be done to a divisor of the nominal fps value
 523     fps = getClosestFramerateStandard(fps, 'STANDARD')
 524   }
 525
 526   command = await presetH264(command, options.inputPath, options.resolution, fps)
 527
 528   if (options.resolution !== undefined) {
 529     // '?x720' or '720x?' for example
 530     const size = options.isPortraitMode === true ? `${options.resolution}x?` : `?x${options.resolution}`
 531     command = command.size(size)
 532   }
 533
 534   if (fps) {
 535     // Hard FPS limits
 536     if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = getClosestFramerateStandard(fps, 'HD_STANDARD')
 537     else if (fps < VIDEO_TRANSCODING_FPS.MIN) fps = VIDEO_TRANSCODING_FPS.MIN
 538
 539     command = command.withFPS(fps)
 540   }
 541
 542   return command
 543 }
 544
 545 async function buildAudioMergeCommand (command: ffmpeg.FfmpegCommand, options: MergeAudioTranscodeOptions) {
 546   command = command.loop(undefined)
 547
 548   command = await presetH264VeryFast(command, options.audioPath, options.resolution)
 549
 550   command = command.input(options.audioPath)
 551                    .videoFilter('scale=trunc(iw/2)*2:trunc(ih/2)*2') // Avoid "height not divisible by 2" error
 552                    .outputOption('-tune stillimage')
 553                    .outputOption('-shortest')
 554
 555   return command
 556 }
 557
 558 function buildOnlyAudioCommand (command: ffmpeg.FfmpegCommand, options: OnlyAudioTranscodeOptions) {
 559   command = presetOnlyAudio(command)
 560
 561   return command
 562 }
 563
 564 function buildQuickTranscodeCommand (command: ffmpeg.FfmpegCommand) {
 565   command = presetCopy(command)
 566
 567   command = command.outputOption('-map_metadata -1') // strip all metadata
 568                    .outputOption('-movflags faststart')
 569
 570   return command
 571 }
 572
 573 async function buildHLSVODCommand (command: ffmpeg.FfmpegCommand, options: HLSTranscodeOptions) {
 574   const videoPath = getHLSVideoPath(options)
 575
 576   if (options.copyCodecs) command = presetCopy(command)
 577   else if (options.resolution === VideoResolution.H_NOVIDEO) command = presetOnlyAudio(command)
 578   else command = await buildx264Command(command, options)
 579
 580   command = command.outputOption('-hls_time 4')
 581                    .outputOption('-hls_list_size 0')
 582                    .outputOption('-hls_playlist_type vod')
 583                    .outputOption('-hls_segment_filename ' + videoPath)
 584                    .outputOption('-hls_segment_type fmp4')
 585                    .outputOption('-f hls')
 586                    .outputOption('-hls_flags single_file')
 587
 588   return command
 589 }
 590
 591 function getHLSVideoPath (options: HLSTranscodeOptions) {
 592   return `${dirname(options.outputPath)}/${options.hlsPlaylist.videoFilename}`
 593 }
 594
 595 async function fixHLSPlaylistIfNeeded (options: TranscodeOptions) {
 596   if (options.type !== 'hls') return
 597
 598   const fileContent = await readFile(options.outputPath)
 599
 600   const videoFileName = options.hlsPlaylist.videoFilename
 601   const videoFilePath = getHLSVideoPath(options)
 602
 603   // Fix wrong mapping with some ffmpeg versions
 604   const newContent = fileContent.toString()
 605                                 .replace(`#EXT-X-MAP:URI="${videoFilePath}",`, `#EXT-X-MAP:URI="${videoFileName}",`)
 606
 607   await writeFile(options.outputPath, newContent)
 608 }
 609
 610 /**
 611  * A slightly customised version of the 'veryfast' x264 preset
 612  *
 613  * The veryfast preset is right in the sweet spot of performance
 614  * and quality. Superfast and ultrafast will give you better
 615  * performance, but then quality is noticeably worse.
 616  */
 617 async function presetH264VeryFast (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 618   let localCommand = await presetH264(command, input, resolution, fps)
 619
 620   localCommand = localCommand.outputOption('-preset:v veryfast')
 621
 622   /*
 623   MAIN reference: https://slhck.info/video/2017/03/01/rate-control.html
 624   Our target situation is closer to a livestream than a stream,
 625   since we want to reduce as much a possible the encoding burden,
 626   although not to the point of a livestream where there is a hard
 627   constraint on the frames per second to be encoded.
 628   */
 629
 630   return localCommand
 631 }
 632
 633 /**
 634  * Standard profile, with variable bitrate audio and faststart.
 635  *
 636  * As for the audio, quality '5' is the highest and ensures 96-112kbps/channel
 637  * See https://trac.ffmpeg.org/wiki/Encode/AAC#fdk_vbr
 638  */
 639 async function presetH264 (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 640   let localCommand = command
 641     .format('mp4')
 642     .videoCodec('libx264')
 643     .outputOption('-movflags faststart')
 644
 645   addDefaultX264Params(localCommand)
 646
 647   const parsedAudio = await audio.get(input)
 648
 649   if (!parsedAudio.audioStream) {
 650     localCommand = localCommand.noAudio()
 651   } else if ((await checkFFmpegEncoders()).get('libfdk_aac')) { // we favor VBR, if a good AAC encoder is available
 652     localCommand = localCommand
 653       .audioCodec('libfdk_aac')
 654       .audioQuality(5)
 655   } else {
 656     // we try to reduce the ceiling bitrate by making rough matches of bitrates
 657     // of course this is far from perfect, but it might save some space in the end
 658     localCommand = localCommand.audioCodec('aac')
 659
 660     const audioCodecName = parsedAudio.audioStream['codec_name']
 661
 662     if (audio.bitrate[audioCodecName]) {
 663       const bitrate = audio.bitrate[audioCodecName](parsedAudio.audioStream['bit_rate'])
 664       if (bitrate !== undefined && bitrate !== -1) localCommand = localCommand.audioBitrate(bitrate)
 665     }
 666   }
 667
 668   if (fps) {
 669     // Constrained Encoding (VBV)
 670     // https://slhck.info/video/2017/03/01/rate-control.html
 671     // https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
 672     const targetBitrate = getTargetBitrate(resolution, fps, VIDEO_TRANSCODING_FPS)
 673     localCommand = localCommand.outputOptions([ `-maxrate ${targetBitrate}`, `-bufsize ${targetBitrate * 2}` ])
 674
 675     // Keyframe interval of 2 seconds for faster seeking and resolution switching.
 676     // https://streaminglearningcenter.com/blogs/whats-the-right-keyframe-interval.html
 677     // https://superuser.com/a/908325
 678     localCommand = localCommand.outputOption(`-g ${fps * 2}`)
 679   }
 680
 681   return localCommand
 682 }
 683
 684 function presetCopy (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 685   return command
 686     .format('mp4')
 687     .videoCodec('copy')
 688     .audioCodec('copy')
 689 }
 690
 691 function presetOnlyAudio (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 692   return command
 693     .format('mp4')
 694     .audioCodec('copy')
 695     .noVideo()
 696 }
 697
 698 function getFFmpeg (input: string) {
 699   // We set cwd explicitly because ffmpeg appears to create temporary files when trancoding which fails in read-only file systems
 700   const command = ffmpeg(input, { niceness: FFMPEG_NICE.TRANSCODING, cwd: CONFIG.STORAGE.TMP_DIR })
 701
 702   if (CONFIG.TRANSCODING.THREADS > 0) {
 703     // If we don't set any threads ffmpeg will chose automatically
 704     command.outputOption('-threads ' + CONFIG.TRANSCODING.THREADS)
 705   }
 706
 707   return command
 708 }