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
 389   for (let i = 0; i < resolutions.length; i++) {
 390     const resolution = resolutions[i]
 391
 392     command.outputOption(`-map [vout${resolution}]`)
 393     command.outputOption(`-c:v:${i} libx264`)
 394     command.outputOption(`-b:v:${i} ${getTargetBitrate(resolution, liveFPS, VIDEO_TRANSCODING_FPS)}`)
 395
 396     command.outputOption(`-map a:0`)
 397     command.outputOption(`-c:a:${i} aac`)
 398
 399     varStreamMap.push(`v:${i},a:${i}`)
 400   }
 401
 402   addDefaultLiveHLSParams(command, outPath, deleteSegments)
 403
 404   command.outputOption('-var_stream_map', varStreamMap.join(' '))
 405
 406   command.run()
 407
 408   return command
 409 }
 410
 411 function runLiveMuxing (rtmpUrl: string, outPath: string, deleteSegments: boolean) {
 412   const command = getFFmpeg(rtmpUrl)
 413   command.inputOption('-fflags nobuffer')
 414
 415   command.outputOption('-c:v copy')
 416   command.outputOption('-c:a copy')
 417   command.outputOption('-map 0:a?')
 418   command.outputOption('-map 0:v?')
 419
 420   addDefaultLiveHLSParams(command, outPath, deleteSegments)
 421
 422   command.run()
 423
 424   return command
 425 }
 426
 427 async function hlsPlaylistToFragmentedMP4 (hlsDirectory: string, segmentFiles: string[], outputPath: string) {
 428   const concatFile = 'concat.txt'
 429   const concatFilePath = join(hlsDirectory, concatFile)
 430   const content = segmentFiles.map(f => 'file ' + f)
 431                               .join('\n')
 432
 433   await writeFile(concatFilePath, content + '\n')
 434
 435   const command = getFFmpeg(concatFilePath)
 436   command.inputOption('-safe 0')
 437   command.inputOption('-f concat')
 438
 439   command.outputOption('-c copy')
 440   command.output(outputPath)
 441
 442   command.run()
 443
 444   function cleaner () {
 445     remove(concatFile)
 446     .catch(err => logger.error('Cannot remove concat file in %s.', hlsDirectory, { err }))
 447   }
 448
 449   return new Promise<string>((res, rej) => {
 450     command.on('error', err => {
 451       cleaner()
 452
 453       rej(err)
 454     })
 455
 456     command.on('end', () => {
 457       cleaner()
 458
 459       res()
 460     })
 461   })
 462 }
 463
 464 // ---------------------------------------------------------------------------
 465
 466 export {
 467   getVideoStreamCodec,
 468   getAudioStreamCodec,
 469   runLiveMuxing,
 470   convertWebPToJPG,
 471   getVideoStreamSize,
 472   getVideoFileResolution,
 473   getMetadataFromFile,
 474   getDurationFromVideoFile,
 475   runLiveTranscoding,
 476   generateImageFromVideoFile,
 477   TranscodeOptions,
 478   TranscodeOptionsType,
 479   transcode,
 480   getVideoFileFPS,
 481   computeResolutionsToTranscode,
 482   audio,
 483   hlsPlaylistToFragmentedMP4,
 484   getVideoFileBitrate,
 485   canDoQuickTranscode
 486 }
 487
 488 // ---------------------------------------------------------------------------
 489
 490 function addDefaultX264Params (command: ffmpeg.FfmpegCommand) {
 491   command.outputOption('-level 3.1') // 3.1 is the minimal resource allocation for our highest supported resolution
 492          .outputOption('-b_strategy 1') // NOTE: b-strategy 1 - heuristic algorithm, 16 is optimal B-frames for it
 493          .outputOption('-bf 16') // NOTE: Why 16: https://github.com/Chocobozzz/PeerTube/pull/774. b-strategy 2 -> B-frames<16
 494          .outputOption('-pix_fmt yuv420p') // allows import of source material with incompatible pixel formats (e.g. MJPEG video)
 495          .outputOption('-map_metadata -1') // strip all metadata
 496 }
 497
 498 function addDefaultLiveHLSParams (command: ffmpeg.FfmpegCommand, outPath: string, deleteSegments: boolean) {
 499   command.outputOption('-hls_time ' + VIDEO_LIVE.SEGMENT_TIME)
 500   command.outputOption('-hls_list_size ' + VIDEO_LIVE.SEGMENTS_LIST_SIZE)
 501
 502   if (deleteSegments === true) {
 503     command.outputOption('-hls_flags delete_segments')
 504   }
 505
 506   command.outputOption(`-hls_segment_filename ${join(outPath, '%v-%d.ts')}`)
 507   command.outputOption('-master_pl_name master.m3u8')
 508   command.outputOption(`-f hls`)
 509
 510   command.output(join(outPath, '%v.m3u8'))
 511 }
 512
 513 async function buildx264Command (command: ffmpeg.FfmpegCommand, options: TranscodeOptions) {
 514   let fps = await getVideoFileFPS(options.inputPath)
 515   if (
 516     // On small/medium resolutions, limit FPS
 517     options.resolution !== undefined &&
 518     options.resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
 519     fps > VIDEO_TRANSCODING_FPS.AVERAGE
 520   ) {
 521     // Get closest standard framerate by modulo: downsampling has to be done to a divisor of the nominal fps value
 522     fps = getClosestFramerateStandard(fps, 'STANDARD')
 523   }
 524
 525   command = await presetH264(command, options.inputPath, options.resolution, fps)
 526
 527   if (options.resolution !== undefined) {
 528     // '?x720' or '720x?' for example
 529     const size = options.isPortraitMode === true ? `${options.resolution}x?` : `?x${options.resolution}`
 530     command = command.size(size)
 531   }
 532
 533   if (fps) {
 534     // Hard FPS limits
 535     if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = getClosestFramerateStandard(fps, 'HD_STANDARD')
 536     else if (fps < VIDEO_TRANSCODING_FPS.MIN) fps = VIDEO_TRANSCODING_FPS.MIN
 537
 538     command = command.withFPS(fps)
 539   }
 540
 541   return command
 542 }
 543
 544 async function buildAudioMergeCommand (command: ffmpeg.FfmpegCommand, options: MergeAudioTranscodeOptions) {
 545   command = command.loop(undefined)
 546
 547   command = await presetH264VeryFast(command, options.audioPath, options.resolution)
 548
 549   command = command.input(options.audioPath)
 550                    .videoFilter('scale=trunc(iw/2)*2:trunc(ih/2)*2') // Avoid "height not divisible by 2" error
 551                    .outputOption('-tune stillimage')
 552                    .outputOption('-shortest')
 553
 554   return command
 555 }
 556
 557 function buildOnlyAudioCommand (command: ffmpeg.FfmpegCommand, options: OnlyAudioTranscodeOptions) {
 558   command = presetOnlyAudio(command)
 559
 560   return command
 561 }
 562
 563 function buildQuickTranscodeCommand (command: ffmpeg.FfmpegCommand) {
 564   command = presetCopy(command)
 565
 566   command = command.outputOption('-map_metadata -1') // strip all metadata
 567                    .outputOption('-movflags faststart')
 568
 569   return command
 570 }
 571
 572 async function buildHLSVODCommand (command: ffmpeg.FfmpegCommand, options: HLSTranscodeOptions) {
 573   const videoPath = getHLSVideoPath(options)
 574
 575   if (options.copyCodecs) command = presetCopy(command)
 576   else if (options.resolution === VideoResolution.H_NOVIDEO) command = presetOnlyAudio(command)
 577   else command = await buildx264Command(command, options)
 578
 579   command = command.outputOption('-hls_time 4')
 580                    .outputOption('-hls_list_size 0')
 581                    .outputOption('-hls_playlist_type vod')
 582                    .outputOption('-hls_segment_filename ' + videoPath)
 583                    .outputOption('-hls_segment_type fmp4')
 584                    .outputOption('-f hls')
 585                    .outputOption('-hls_flags single_file')
 586
 587   return command
 588 }
 589
 590 function getHLSVideoPath (options: HLSTranscodeOptions) {
 591   return `${dirname(options.outputPath)}/${options.hlsPlaylist.videoFilename}`
 592 }
 593
 594 async function fixHLSPlaylistIfNeeded (options: TranscodeOptions) {
 595   if (options.type !== 'hls') return
 596
 597   const fileContent = await readFile(options.outputPath)
 598
 599   const videoFileName = options.hlsPlaylist.videoFilename
 600   const videoFilePath = getHLSVideoPath(options)
 601
 602   // Fix wrong mapping with some ffmpeg versions
 603   const newContent = fileContent.toString()
 604                                 .replace(`#EXT-X-MAP:URI="${videoFilePath}",`, `#EXT-X-MAP:URI="${videoFileName}",`)
 605
 606   await writeFile(options.outputPath, newContent)
 607 }
 608
 609 /**
 610  * A slightly customised version of the 'veryfast' x264 preset
 611  *
 612  * The veryfast preset is right in the sweet spot of performance
 613  * and quality. Superfast and ultrafast will give you better
 614  * performance, but then quality is noticeably worse.
 615  */
 616 async function presetH264VeryFast (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 617   let localCommand = await presetH264(command, input, resolution, fps)
 618
 619   localCommand = localCommand.outputOption('-preset:v veryfast')
 620
 621   /*
 622   MAIN reference: https://slhck.info/video/2017/03/01/rate-control.html
 623   Our target situation is closer to a livestream than a stream,
 624   since we want to reduce as much a possible the encoding burden,
 625   although not to the point of a livestream where there is a hard
 626   constraint on the frames per second to be encoded.
 627   */
 628
 629   return localCommand
 630 }
 631
 632 /**
 633  * Standard profile, with variable bitrate audio and faststart.
 634  *
 635  * As for the audio, quality '5' is the highest and ensures 96-112kbps/channel
 636  * See https://trac.ffmpeg.org/wiki/Encode/AAC#fdk_vbr
 637  */
 638 async function presetH264 (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 639   let localCommand = command
 640     .format('mp4')
 641     .videoCodec('libx264')
 642     .outputOption('-movflags faststart')
 643
 644   addDefaultX264Params(localCommand)
 645
 646   const parsedAudio = await audio.get(input)
 647
 648   if (!parsedAudio.audioStream) {
 649     localCommand = localCommand.noAudio()
 650   } else if ((await checkFFmpegEncoders()).get('libfdk_aac')) { // we favor VBR, if a good AAC encoder is available
 651     localCommand = localCommand
 652       .audioCodec('libfdk_aac')
 653       .audioQuality(5)
 654   } else {
 655     // we try to reduce the ceiling bitrate by making rough matches of bitrates
 656     // of course this is far from perfect, but it might save some space in the end
 657     localCommand = localCommand.audioCodec('aac')
 658
 659     const audioCodecName = parsedAudio.audioStream['codec_name']
 660
 661     if (audio.bitrate[audioCodecName]) {
 662       const bitrate = audio.bitrate[audioCodecName](parsedAudio.audioStream['bit_rate'])
 663       if (bitrate !== undefined && bitrate !== -1) localCommand = localCommand.audioBitrate(bitrate)
 664     }
 665   }
 666
 667   if (fps) {
 668     // Constrained Encoding (VBV)
 669     // https://slhck.info/video/2017/03/01/rate-control.html
 670     // https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
 671     const targetBitrate = getTargetBitrate(resolution, fps, VIDEO_TRANSCODING_FPS)
 672     localCommand = localCommand.outputOptions([ `-maxrate ${targetBitrate}`, `-bufsize ${targetBitrate * 2}` ])
 673
 674     // Keyframe interval of 2 seconds for faster seeking and resolution switching.
 675     // https://streaminglearningcenter.com/blogs/whats-the-right-keyframe-interval.html
 676     // https://superuser.com/a/908325
 677     localCommand = localCommand.outputOption(`-g ${fps * 2}`)
 678   }
 679
 680   return localCommand
 681 }
 682
 683 function presetCopy (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 684   return command
 685     .format('mp4')
 686     .videoCodec('copy')
 687     .audioCodec('copy')
 688 }
 689
 690 function presetOnlyAudio (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 691   return command
 692     .format('mp4')
 693     .audioCodec('copy')
 694     .noVideo()
 695 }
 696
 697 function getFFmpeg (input: string) {
 698   // We set cwd explicitly because ffmpeg appears to create temporary files when trancoding which fails in read-only file systems
 699   const command = ffmpeg(input, { niceness: FFMPEG_NICE.TRANSCODING, cwd: CONFIG.STORAGE.TMP_DIR })
 700
 701   if (CONFIG.TRANSCODING.THREADS > 0) {
 702     // If we don't set any threads ffmpeg will chose automatically
 703     command.outputOption('-threads ' + CONFIG.TRANSCODING.THREADS)
 704   }
 705
 706   return command
 707 }