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[], fps, 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   command.outputOption('-b_strategy 1')
 379   command.outputOption('-bf 16')
 380   command.outputOption('-preset superfast')
 381   command.outputOption('-level 3.1')
 382   command.outputOption('-map_metadata -1')
 383   command.outputOption('-pix_fmt yuv420p')
 384   command.outputOption('-max_muxing_queue_size 1024')
 385   command.outputOption('-g ' + (fps * 2))
 386
 387   for (let i = 0; i < resolutions.length; i++) {
 388     const resolution = resolutions[i]
 389
 390     command.outputOption(`-map [vout${resolution}]`)
 391     command.outputOption(`-c:v:${i} libx264`)
 392     command.outputOption(`-b:v:${i} ${getTargetBitrate(resolution, fps, VIDEO_TRANSCODING_FPS)}`)
 393
 394     command.outputOption(`-map a:0`)
 395     command.outputOption(`-c:a:${i} aac`)
 396
 397     varStreamMap.push(`v:${i},a:${i}`)
 398   }
 399
 400   addDefaultLiveHLSParams(command, outPath, deleteSegments)
 401
 402   command.outputOption('-var_stream_map', varStreamMap.join(' '))
 403
 404   command.run()
 405
 406   return command
 407 }
 408
 409 function runLiveMuxing (rtmpUrl: string, outPath: string, deleteSegments: boolean) {
 410   const command = getFFmpeg(rtmpUrl)
 411   command.inputOption('-fflags nobuffer')
 412
 413   command.outputOption('-c:v copy')
 414   command.outputOption('-c:a copy')
 415   command.outputOption('-map 0:a?')
 416   command.outputOption('-map 0:v?')
 417
 418   addDefaultLiveHLSParams(command, outPath, deleteSegments)
 419
 420   command.run()
 421
 422   return command
 423 }
 424
 425 async function hlsPlaylistToFragmentedMP4 (hlsDirectory: string, segmentFiles: string[], outputPath: string) {
 426   const concatFile = 'concat.txt'
 427   const concatFilePath = join(hlsDirectory, concatFile)
 428   const content = segmentFiles.map(f => 'file ' + f)
 429                               .join('\n')
 430
 431   await writeFile(concatFilePath, content + '\n')
 432
 433   const command = getFFmpeg(concatFilePath)
 434   command.inputOption('-safe 0')
 435   command.inputOption('-f concat')
 436
 437   command.outputOption('-c copy')
 438   command.output(outputPath)
 439
 440   command.run()
 441
 442   function cleaner () {
 443     remove(concatFilePath)
 444       .catch(err => logger.error('Cannot remove concat file in %s.', hlsDirectory, { err }))
 445   }
 446
 447   return new Promise<string>((res, rej) => {
 448     command.on('error', err => {
 449       cleaner()
 450
 451       rej(err)
 452     })
 453
 454     command.on('end', () => {
 455       cleaner()
 456
 457       res()
 458     })
 459   })
 460 }
 461
 462 // ---------------------------------------------------------------------------
 463
 464 export {
 465   getVideoStreamCodec,
 466   getAudioStreamCodec,
 467   runLiveMuxing,
 468   convertWebPToJPG,
 469   getVideoStreamSize,
 470   getVideoFileResolution,
 471   getMetadataFromFile,
 472   getDurationFromVideoFile,
 473   runLiveTranscoding,
 474   generateImageFromVideoFile,
 475   TranscodeOptions,
 476   TranscodeOptionsType,
 477   transcode,
 478   getVideoFileFPS,
 479   computeResolutionsToTranscode,
 480   audio,
 481   hlsPlaylistToFragmentedMP4,
 482   getVideoFileBitrate,
 483   canDoQuickTranscode
 484 }
 485
 486 // ---------------------------------------------------------------------------
 487
 488 function addDefaultX264Params (command: ffmpeg.FfmpegCommand) {
 489   command.outputOption('-level 3.1') // 3.1 is the minimal resource allocation for our highest supported resolution
 490          .outputOption('-b_strategy 1') // NOTE: b-strategy 1 - heuristic algorithm, 16 is optimal B-frames for it
 491          .outputOption('-bf 16') // NOTE: Why 16: https://github.com/Chocobozzz/PeerTube/pull/774. b-strategy 2 -> B-frames<16
 492          .outputOption('-pix_fmt yuv420p') // allows import of source material with incompatible pixel formats (e.g. MJPEG video)
 493          .outputOption('-map_metadata -1') // strip all metadata
 494 }
 495
 496 function addDefaultLiveHLSParams (command: ffmpeg.FfmpegCommand, outPath: string, deleteSegments: boolean) {
 497   command.outputOption('-hls_time ' + VIDEO_LIVE.SEGMENT_TIME_SECONDS)
 498   command.outputOption('-hls_list_size ' + VIDEO_LIVE.SEGMENTS_LIST_SIZE)
 499
 500   if (deleteSegments === true) {
 501     command.outputOption('-hls_flags delete_segments')
 502   }
 503
 504   command.outputOption(`-hls_segment_filename ${join(outPath, '%v-%d.ts')}`)
 505   command.outputOption('-master_pl_name master.m3u8')
 506   command.outputOption(`-f hls`)
 507
 508   command.output(join(outPath, '%v.m3u8'))
 509 }
 510
 511 async function buildx264Command (command: ffmpeg.FfmpegCommand, options: TranscodeOptions) {
 512   let fps = await getVideoFileFPS(options.inputPath)
 513   if (
 514     // On small/medium resolutions, limit FPS
 515     options.resolution !== undefined &&
 516     options.resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
 517     fps > VIDEO_TRANSCODING_FPS.AVERAGE
 518   ) {
 519     // Get closest standard framerate by modulo: downsampling has to be done to a divisor of the nominal fps value
 520     fps = getClosestFramerateStandard(fps, 'STANDARD')
 521   }
 522
 523   command = await presetH264(command, options.inputPath, options.resolution, fps)
 524
 525   if (options.resolution !== undefined) {
 526     // '?x720' or '720x?' for example
 527     const size = options.isPortraitMode === true ? `${options.resolution}x?` : `?x${options.resolution}`
 528     command = command.size(size)
 529   }
 530
 531   if (fps) {
 532     // Hard FPS limits
 533     if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = getClosestFramerateStandard(fps, 'HD_STANDARD')
 534     else if (fps < VIDEO_TRANSCODING_FPS.MIN) fps = VIDEO_TRANSCODING_FPS.MIN
 535
 536     command = command.withFPS(fps)
 537   }
 538
 539   return command
 540 }
 541
 542 async function buildAudioMergeCommand (command: ffmpeg.FfmpegCommand, options: MergeAudioTranscodeOptions) {
 543   command = command.loop(undefined)
 544
 545   command = await presetH264VeryFast(command, options.audioPath, options.resolution)
 546
 547   command = command.input(options.audioPath)
 548                    .videoFilter('scale=trunc(iw/2)*2:trunc(ih/2)*2') // Avoid "height not divisible by 2" error
 549                    .outputOption('-tune stillimage')
 550                    .outputOption('-shortest')
 551
 552   return command
 553 }
 554
 555 function buildOnlyAudioCommand (command: ffmpeg.FfmpegCommand, options: OnlyAudioTranscodeOptions) {
 556   command = presetOnlyAudio(command)
 557
 558   return command
 559 }
 560
 561 function buildQuickTranscodeCommand (command: ffmpeg.FfmpegCommand) {
 562   command = presetCopy(command)
 563
 564   command = command.outputOption('-map_metadata -1') // strip all metadata
 565                    .outputOption('-movflags faststart')
 566
 567   return command
 568 }
 569
 570 async function buildHLSVODCommand (command: ffmpeg.FfmpegCommand, options: HLSTranscodeOptions) {
 571   const videoPath = getHLSVideoPath(options)
 572
 573   if (options.copyCodecs) command = presetCopy(command)
 574   else if (options.resolution === VideoResolution.H_NOVIDEO) command = presetOnlyAudio(command)
 575   else command = await buildx264Command(command, options)
 576
 577   command = command.outputOption('-hls_time 4')
 578                    .outputOption('-hls_list_size 0')
 579                    .outputOption('-hls_playlist_type vod')
 580                    .outputOption('-hls_segment_filename ' + videoPath)
 581                    .outputOption('-hls_segment_type fmp4')
 582                    .outputOption('-f hls')
 583                    .outputOption('-hls_flags single_file')
 584
 585   return command
 586 }
 587
 588 function getHLSVideoPath (options: HLSTranscodeOptions) {
 589   return `${dirname(options.outputPath)}/${options.hlsPlaylist.videoFilename}`
 590 }
 591
 592 async function fixHLSPlaylistIfNeeded (options: TranscodeOptions) {
 593   if (options.type !== 'hls') return
 594
 595   const fileContent = await readFile(options.outputPath)
 596
 597   const videoFileName = options.hlsPlaylist.videoFilename
 598   const videoFilePath = getHLSVideoPath(options)
 599
 600   // Fix wrong mapping with some ffmpeg versions
 601   const newContent = fileContent.toString()
 602                                 .replace(`#EXT-X-MAP:URI="${videoFilePath}",`, `#EXT-X-MAP:URI="${videoFileName}",`)
 603
 604   await writeFile(options.outputPath, newContent)
 605 }
 606
 607 /**
 608  * A slightly customised version of the 'veryfast' x264 preset
 609  *
 610  * The veryfast preset is right in the sweet spot of performance
 611  * and quality. Superfast and ultrafast will give you better
 612  * performance, but then quality is noticeably worse.
 613  */
 614 async function presetH264VeryFast (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 615   let localCommand = await presetH264(command, input, resolution, fps)
 616
 617   localCommand = localCommand.outputOption('-preset:v veryfast')
 618
 619   /*
 620   MAIN reference: https://slhck.info/video/2017/03/01/rate-control.html
 621   Our target situation is closer to a livestream than a stream,
 622   since we want to reduce as much a possible the encoding burden,
 623   although not to the point of a livestream where there is a hard
 624   constraint on the frames per second to be encoded.
 625   */
 626
 627   return localCommand
 628 }
 629
 630 /**
 631  * Standard profile, with variable bitrate audio and faststart.
 632  *
 633  * As for the audio, quality '5' is the highest and ensures 96-112kbps/channel
 634  * See https://trac.ffmpeg.org/wiki/Encode/AAC#fdk_vbr
 635  */
 636 async function presetH264 (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 637   let localCommand = command
 638     .format('mp4')
 639     .videoCodec('libx264')
 640     .outputOption('-movflags faststart')
 641
 642   addDefaultX264Params(localCommand)
 643
 644   const parsedAudio = await audio.get(input)
 645
 646   if (!parsedAudio.audioStream) {
 647     localCommand = localCommand.noAudio()
 648   } else if ((await checkFFmpegEncoders()).get('libfdk_aac')) { // we favor VBR, if a good AAC encoder is available
 649     localCommand = localCommand
 650       .audioCodec('libfdk_aac')
 651       .audioQuality(5)
 652   } else {
 653     // we try to reduce the ceiling bitrate by making rough matches of bitrates
 654     // of course this is far from perfect, but it might save some space in the end
 655     localCommand = localCommand.audioCodec('aac')
 656
 657     const audioCodecName = parsedAudio.audioStream['codec_name']
 658
 659     if (audio.bitrate[audioCodecName]) {
 660       const bitrate = audio.bitrate[audioCodecName](parsedAudio.audioStream['bit_rate'])
 661       if (bitrate !== undefined && bitrate !== -1) localCommand = localCommand.audioBitrate(bitrate)
 662     }
 663   }
 664
 665   if (fps) {
 666     // Constrained Encoding (VBV)
 667     // https://slhck.info/video/2017/03/01/rate-control.html
 668     // https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
 669     const targetBitrate = getTargetBitrate(resolution, fps, VIDEO_TRANSCODING_FPS)
 670     localCommand = localCommand.outputOptions([ `-maxrate ${targetBitrate}`, `-bufsize ${targetBitrate * 2}` ])
 671
 672     // Keyframe interval of 2 seconds for faster seeking and resolution switching.
 673     // https://streaminglearningcenter.com/blogs/whats-the-right-keyframe-interval.html
 674     // https://superuser.com/a/908325
 675     localCommand = localCommand.outputOption(`-g ${fps * 2}`)
 676   }
 677
 678   return localCommand
 679 }
 680
 681 function presetCopy (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 682   return command
 683     .format('mp4')
 684     .videoCodec('copy')
 685     .audioCodec('copy')
 686 }
 687
 688 function presetOnlyAudio (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 689   return command
 690     .format('mp4')
 691     .audioCodec('copy')
 692     .noVideo()
 693 }
 694
 695 function getFFmpeg (input: string) {
 696   // We set cwd explicitly because ffmpeg appears to create temporary files when trancoding which fails in read-only file systems
 697   const command = ffmpeg(input, { niceness: FFMPEG_NICE.TRANSCODING, cwd: CONFIG.STORAGE.TMP_DIR })
 698
 699   if (CONFIG.TRANSCODING.THREADS > 0) {
 700     // If we don't set any threads ffmpeg will chose automatically
 701     command.outputOption('-threads ' + CONFIG.TRANSCODING.THREADS)
 702   }
 703
 704   return command
 705 }