server/helpers/ffmpeg/framerate.ts

   1 import { VIDEO_TRANSCODING_FPS } from '@server/initializers/constants'
   2 import { VideoResolution } from '@shared/models'
   3
   4 export function computeOutputFPS (options: {
   5   inputFPS: number
   6   resolution: VideoResolution
   7 }) {
   8   const { resolution } = options
   9
  10   let fps = options.inputFPS
  11
  12   if (
  13     // On small/medium resolutions, limit FPS
  14     resolution !== undefined &&
  15     resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
  16     fps > VIDEO_TRANSCODING_FPS.AVERAGE
  17   ) {
  18     // Get closest standard framerate by modulo: downsampling has to be done to a divisor of the nominal fps value
  19     fps = getClosestFramerateStandard({ fps, type: 'STANDARD' })
  20   }
  21
  22   // Hard FPS limits
  23   if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = getClosestFramerateStandard({ fps, type: 'HD_STANDARD' })
  24
  25   if (fps < VIDEO_TRANSCODING_FPS.MIN) {
  26     throw new Error(`Cannot compute FPS because ${fps} is lower than our minimum value ${VIDEO_TRANSCODING_FPS.MIN}`)
  27   }
  28
  29   return fps
  30 }
  31
  32 // ---------------------------------------------------------------------------
  33 // Private
  34 // ---------------------------------------------------------------------------
  35
  36 function getClosestFramerateStandard (options: {
  37   fps: number
  38   type: 'HD_STANDARD' | 'STANDARD'
  39 }) {
  40   const { fps, type } = options
  41
  42   return VIDEO_TRANSCODING_FPS[type].slice(0)
  43                                     .sort((a, b) => fps % a - fps % b)[0]
  44 }