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