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_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[]) {
 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)
 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) {
 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)
 421
 422   command.run()
 423
 424   return command
 425 }
 426
 427 // ---------------------------------------------------------------------------
 428
 429 export {
 430   getVideoStreamCodec,
 431   getAudioStreamCodec,
 432   runLiveMuxing,
 433   convertWebPToJPG,
 434   getVideoStreamSize,
 435   getVideoFileResolution,
 436   getMetadataFromFile,
 437   getDurationFromVideoFile,
 438   runLiveTranscoding,
 439   generateImageFromVideoFile,
 440   TranscodeOptions,
 441   TranscodeOptionsType,
 442   transcode,
 443   getVideoFileFPS,
 444   computeResolutionsToTranscode,
 445   audio,
 446   getVideoFileBitrate,
 447   canDoQuickTranscode
 448 }
 449
 450 // ---------------------------------------------------------------------------
 451
 452 function addDefaultX264Params (command: ffmpeg.FfmpegCommand) {
 453   command.outputOption('-level 3.1') // 3.1 is the minimal resource allocation for our highest supported resolution
 454          .outputOption('-b_strategy 1') // NOTE: b-strategy 1 - heuristic algorithm, 16 is optimal B-frames for it
 455          .outputOption('-bf 16') // NOTE: Why 16: https://github.com/Chocobozzz/PeerTube/pull/774. b-strategy 2 -> B-frames<16
 456          .outputOption('-pix_fmt yuv420p') // allows import of source material with incompatible pixel formats (e.g. MJPEG video)
 457          .outputOption('-map_metadata -1') // strip all metadata
 458 }
 459
 460 function addDefaultLiveHLSParams (command: ffmpeg.FfmpegCommand, outPath: string) {
 461   command.outputOption('-hls_time 4')
 462   command.outputOption('-hls_list_size 15')
 463   command.outputOption('-hls_flags delete_segments')
 464   command.outputOption(`-hls_segment_filename ${join(outPath, '%v-%d.ts')}`)
 465   command.outputOption('-master_pl_name master.m3u8')
 466   command.outputOption(`-f hls`)
 467
 468   command.output(join(outPath, '%v.m3u8'))
 469 }
 470
 471 async function buildx264Command (command: ffmpeg.FfmpegCommand, options: TranscodeOptions) {
 472   let fps = await getVideoFileFPS(options.inputPath)
 473   if (
 474     // On small/medium resolutions, limit FPS
 475     options.resolution !== undefined &&
 476     options.resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
 477     fps > VIDEO_TRANSCODING_FPS.AVERAGE
 478   ) {
 479     // Get closest standard framerate by modulo: downsampling has to be done to a divisor of the nominal fps value
 480     fps = getClosestFramerateStandard(fps, 'STANDARD')
 481   }
 482
 483   command = await presetH264(command, options.inputPath, options.resolution, fps)
 484
 485   if (options.resolution !== undefined) {
 486     // '?x720' or '720x?' for example
 487     const size = options.isPortraitMode === true ? `${options.resolution}x?` : `?x${options.resolution}`
 488     command = command.size(size)
 489   }
 490
 491   if (fps) {
 492     // Hard FPS limits
 493     if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = getClosestFramerateStandard(fps, 'HD_STANDARD')
 494     else if (fps < VIDEO_TRANSCODING_FPS.MIN) fps = VIDEO_TRANSCODING_FPS.MIN
 495
 496     command = command.withFPS(fps)
 497   }
 498
 499   return command
 500 }
 501
 502 async function buildAudioMergeCommand (command: ffmpeg.FfmpegCommand, options: MergeAudioTranscodeOptions) {
 503   command = command.loop(undefined)
 504
 505   command = await presetH264VeryFast(command, options.audioPath, options.resolution)
 506
 507   command = command.input(options.audioPath)
 508                    .videoFilter('scale=trunc(iw/2)*2:trunc(ih/2)*2') // Avoid "height not divisible by 2" error
 509                    .outputOption('-tune stillimage')
 510                    .outputOption('-shortest')
 511
 512   return command
 513 }
 514
 515 function buildOnlyAudioCommand (command: ffmpeg.FfmpegCommand, options: OnlyAudioTranscodeOptions) {
 516   command = presetOnlyAudio(command)
 517
 518   return command
 519 }
 520
 521 function buildQuickTranscodeCommand (command: ffmpeg.FfmpegCommand) {
 522   command = presetCopy(command)
 523
 524   command = command.outputOption('-map_metadata -1') // strip all metadata
 525                    .outputOption('-movflags faststart')
 526
 527   return command
 528 }
 529
 530 async function buildHLSVODCommand (command: ffmpeg.FfmpegCommand, options: HLSTranscodeOptions) {
 531   const videoPath = getHLSVideoPath(options)
 532
 533   if (options.copyCodecs) command = presetCopy(command)
 534   else if (options.resolution === VideoResolution.H_NOVIDEO) command = presetOnlyAudio(command)
 535   else command = await buildx264Command(command, options)
 536
 537   command = command.outputOption('-hls_time 4')
 538                    .outputOption('-hls_list_size 0')
 539                    .outputOption('-hls_playlist_type vod')
 540                    .outputOption('-hls_segment_filename ' + videoPath)
 541                    .outputOption('-hls_segment_type fmp4')
 542                    .outputOption('-f hls')
 543                    .outputOption('-hls_flags single_file')
 544
 545   return command
 546 }
 547
 548 function getHLSVideoPath (options: HLSTranscodeOptions) {
 549   return `${dirname(options.outputPath)}/${options.hlsPlaylist.videoFilename}`
 550 }
 551
 552 async function fixHLSPlaylistIfNeeded (options: TranscodeOptions) {
 553   if (options.type !== 'hls') return
 554
 555   const fileContent = await readFile(options.outputPath)
 556
 557   const videoFileName = options.hlsPlaylist.videoFilename
 558   const videoFilePath = getHLSVideoPath(options)
 559
 560   // Fix wrong mapping with some ffmpeg versions
 561   const newContent = fileContent.toString()
 562                                 .replace(`#EXT-X-MAP:URI="${videoFilePath}",`, `#EXT-X-MAP:URI="${videoFileName}",`)
 563
 564   await writeFile(options.outputPath, newContent)
 565 }
 566
 567 /**
 568  * A slightly customised version of the 'veryfast' x264 preset
 569  *
 570  * The veryfast preset is right in the sweet spot of performance
 571  * and quality. Superfast and ultrafast will give you better
 572  * performance, but then quality is noticeably worse.
 573  */
 574 async function presetH264VeryFast (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 575   let localCommand = await presetH264(command, input, resolution, fps)
 576
 577   localCommand = localCommand.outputOption('-preset:v veryfast')
 578
 579   /*
 580   MAIN reference: https://slhck.info/video/2017/03/01/rate-control.html
 581   Our target situation is closer to a livestream than a stream,
 582   since we want to reduce as much a possible the encoding burden,
 583   although not to the point of a livestream where there is a hard
 584   constraint on the frames per second to be encoded.
 585   */
 586
 587   return localCommand
 588 }
 589
 590 /**
 591  * Standard profile, with variable bitrate audio and faststart.
 592  *
 593  * As for the audio, quality '5' is the highest and ensures 96-112kbps/channel
 594  * See https://trac.ffmpeg.org/wiki/Encode/AAC#fdk_vbr
 595  */
 596 async function presetH264 (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
 597   let localCommand = command
 598     .format('mp4')
 599     .videoCodec('libx264')
 600     .outputOption('-movflags faststart')
 601
 602   addDefaultX264Params(localCommand)
 603
 604   const parsedAudio = await audio.get(input)
 605
 606   if (!parsedAudio.audioStream) {
 607     localCommand = localCommand.noAudio()
 608   } else if ((await checkFFmpegEncoders()).get('libfdk_aac')) { // we favor VBR, if a good AAC encoder is available
 609     localCommand = localCommand
 610       .audioCodec('libfdk_aac')
 611       .audioQuality(5)
 612   } else {
 613     // we try to reduce the ceiling bitrate by making rough matches of bitrates
 614     // of course this is far from perfect, but it might save some space in the end
 615     localCommand = localCommand.audioCodec('aac')
 616
 617     const audioCodecName = parsedAudio.audioStream['codec_name']
 618
 619     if (audio.bitrate[audioCodecName]) {
 620       const bitrate = audio.bitrate[audioCodecName](parsedAudio.audioStream['bit_rate'])
 621       if (bitrate !== undefined && bitrate !== -1) localCommand = localCommand.audioBitrate(bitrate)
 622     }
 623   }
 624
 625   if (fps) {
 626     // Constrained Encoding (VBV)
 627     // https://slhck.info/video/2017/03/01/rate-control.html
 628     // https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
 629     const targetBitrate = getTargetBitrate(resolution, fps, VIDEO_TRANSCODING_FPS)
 630     localCommand = localCommand.outputOptions([ `-maxrate ${targetBitrate}`, `-bufsize ${targetBitrate * 2}` ])
 631
 632     // Keyframe interval of 2 seconds for faster seeking and resolution switching.
 633     // https://streaminglearningcenter.com/blogs/whats-the-right-keyframe-interval.html
 634     // https://superuser.com/a/908325
 635     localCommand = localCommand.outputOption(`-g ${fps * 2}`)
 636   }
 637
 638   return localCommand
 639 }
 640
 641 function presetCopy (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 642   return command
 643     .format('mp4')
 644     .videoCodec('copy')
 645     .audioCodec('copy')
 646 }
 647
 648 function presetOnlyAudio (command: ffmpeg.FfmpegCommand): ffmpeg.FfmpegCommand {
 649   return command
 650     .format('mp4')
 651     .audioCodec('copy')
 652     .noVideo()
 653 }
 654
 655 function getFFmpeg (input: string) {
 656   // We set cwd explicitly because ffmpeg appears to create temporary files when trancoding which fails in read-only file systems
 657   const command = ffmpeg(input, { niceness: FFMPEG_NICE.TRANSCODING, cwd: CONFIG.STORAGE.TMP_DIR })
 658
 659   if (CONFIG.TRANSCODING.THREADS > 0) {
 660     // If we don't set any threads ffmpeg will chose automatically
 661     command.outputOption('-threads ' + CONFIG.TRANSCODING.THREADS)
 662   }
 663
 664   return command
 665 }