PeerTube/server/helpers/ffmpeg-utils.ts

import * as ffmpeg from 'fluent-ffmpeg'
import { join } from 'path'
import { VideoResolution, getTargetBitrate } from '../../shared/models/videos'
import { CONFIG, FFMPEG_NICE, VIDEO_TRANSCODING_FPS } from '../initializers'
import { processImage } from './image-utils'
import { logger } from './logger'
import { checkFFmpegEncoders } from '../initializers/checker-before-init'
import { remove } from 'fs-extra'

function computeResolutionsToTranscode (videoFileHeight: number) {
  const resolutionsEnabled: number[] = []
  const configResolutions = CONFIG.TRANSCODING.RESOLUTIONS

  // Put in the order we want to proceed jobs
  const resolutions = [
    VideoResolution.H_480P,
    VideoResolution.H_360P,
    VideoResolution.H_720P,
    VideoResolution.H_240P,
    VideoResolution.H_1080P
  ]

  for (const resolution of resolutions) {
    if (configResolutions[ resolution + 'p' ] === true && videoFileHeight > resolution) {
      resolutionsEnabled.push(resolution)
    }
  }

  return resolutionsEnabled
}

async function getVideoFileResolution (path: string) {
  const videoStream = await getVideoFileStream(path)

  return {
    videoFileResolution: Math.min(videoStream.height, videoStream.width),
    isPortraitMode: videoStream.height > videoStream.width
  }
}

async function getVideoFileFPS (path: string) {
  const videoStream = await getVideoFileStream(path)

  for (const key of [ 'r_frame_rate' , 'avg_frame_rate' ]) {
    const valuesText: string = videoStream[key]
    if (!valuesText) continue

    const [ frames, seconds ] = valuesText.split('/')
    if (!frames || !seconds) continue

    const result = parseInt(frames, 10) / parseInt(seconds, 10)
    if (result > 0) return Math.round(result)
  }

  return 0
}

async function getVideoFileBitrate (path: string) {
  return new Promise<number>((res, rej) => {
    ffmpeg.ffprobe(path, (err, metadata) => {
      if (err) return rej(err)

      return res(metadata.format.bit_rate)
    })
  })
}

function getDurationFromVideoFile (path: string) {
  return new Promise<number>((res, rej) => {
    ffmpeg.ffprobe(path, (err, metadata) => {
      if (err) return rej(err)

      return res(Math.floor(metadata.format.duration))
    })
  })
}

async function generateImageFromVideoFile (fromPath: string, folder: string, imageName: string, size: { width: number, height: number }) {
  const pendingImageName = 'pending-' + imageName

  const options = {
    filename: pendingImageName,
    count: 1,
    folder
  }

  const pendingImagePath = join(folder, pendingImageName)

  try {
    await new Promise<string>((res, rej) => {
      ffmpeg(fromPath, { niceness: FFMPEG_NICE.THUMBNAIL })
        .on('error', rej)
        .on('end', () => res(imageName))
        .thumbnail(options)
    })

    const destination = join(folder, imageName)
    await processImage({ path: pendingImagePath }, destination, size)
  } catch (err) {
    logger.error('Cannot generate image from video %s.', fromPath, { err })

    try {
      await remove(pendingImagePath)
    } catch (err) {
      logger.debug('Cannot remove pending image path after generation error.', { err })
    }
  }
}

type TranscodeOptions = {
  inputPath: string
  outputPath: string
  resolution?: VideoResolution
  isPortraitMode?: boolean
}

function transcode (options: TranscodeOptions) {
  return new Promise<void>(async (res, rej) => {
    let fps = await getVideoFileFPS(options.inputPath)
    // On small/medium resolutions, limit FPS
    if (
      options.resolution !== undefined &&
      options.resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
      fps > VIDEO_TRANSCODING_FPS.AVERAGE
    ) {
      fps = VIDEO_TRANSCODING_FPS.AVERAGE
    }

    let command = ffmpeg(options.inputPath, { niceness: FFMPEG_NICE.TRANSCODING })
                    .output(options.outputPath)
    command = await presetH264(command, options.resolution, fps)

    if (CONFIG.TRANSCODING.THREADS > 0) {
      // if we don't set any threads ffmpeg will chose automatically
      command = command.outputOption('-threads ' + CONFIG.TRANSCODING.THREADS)
    }

    if (options.resolution !== undefined) {
      // '?x720' or '720x?' for example
      const size = options.isPortraitMode === true ? `${options.resolution}x?` : `?x${options.resolution}`
      command = command.size(size)
    }

    if (fps) {
      // Hard FPS limits
      if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = VIDEO_TRANSCODING_FPS.MAX
      else if (fps < VIDEO_TRANSCODING_FPS.MIN) fps = VIDEO_TRANSCODING_FPS.MIN

      command = command.withFPS(fps)
    }

    command
      .on('error', (err, stdout, stderr) => {
        logger.error('Error in transcoding job.', { stdout, stderr })
        return rej(err)
      })
      .on('end', res)
      .run()
  })
}

// ---------------------------------------------------------------------------

export {
  getVideoFileResolution,
  getDurationFromVideoFile,
  generateImageFromVideoFile,
  transcode,
  getVideoFileFPS,
  computeResolutionsToTranscode,
  audio,
  getVideoFileBitrate
}

// ---------------------------------------------------------------------------

function getVideoFileStream (path: string) {
  return new Promise<any>((res, rej) => {
    ffmpeg.ffprobe(path, (err, metadata) => {
      if (err) return rej(err)

      const videoStream = metadata.streams.find(s => s.codec_type === 'video')
      if (!videoStream) throw new Error('Cannot find video stream of ' + path)

      return res(videoStream)
    })
  })
}

/**
 * A slightly customised version of the 'veryfast' x264 preset
 *
 * The veryfast preset is right in the sweet spot of performance
 * and quality. Superfast and ultrafast will give you better
 * performance, but then quality is noticeably worse.
 */
async function presetH264VeryFast (ffmpeg: ffmpeg, resolution: VideoResolution, fps: number): ffmpeg {
  const localFfmpeg = await presetH264(ffmpeg, resolution, fps)
  localFfmpeg
    .outputOption('-preset:v veryfast')
    .outputOption(['--aq-mode=2', '--aq-strength=1.3'])
  /*
  MAIN reference: https://slhck.info/video/2017/03/01/rate-control.html
  Our target situation is closer to a livestream than a stream,
  since we want to reduce as much a possible the encoding burden,
  altough not to the point of a livestream where there is a hard
  constraint on the frames per second to be encoded.

  why '--aq-mode=2 --aq-strength=1.3' instead of '-profile:v main'?
    Make up for most of the loss of grain and macroblocking
    with less computing power.
  */
}

/**
 * A preset optimised for a stillimage audio video
 */
async function presetStillImageWithAudio (ffmpeg: ffmpeg, resolution: VideoResolution, fps: number): ffmpeg {
  const localFfmpeg = await presetH264VeryFast(ffmpeg, resolution, fps)
  localFfmpeg
    .outputOption('-tune stillimage')
}

/**
 * A toolbox to play with audio
 */
namespace audio {
  export const get = (_ffmpeg, pos: number | string = 0) => {
    // without position, ffprobe considers the last input only
    // we make it consider the first input only
    // if you pass a file path to pos, then ffprobe acts on that file directly
    return new Promise<{ absolutePath: string, audioStream?: any }>((res, rej) => {
      _ffmpeg.ffprobe(pos, (err,data) => {
        if (err) return rej(err)

        if ('streams' in data) {
          const audioStream = data['streams'].find(stream => stream['codec_type'] === 'audio')
          if (audioStream) {
            return res({
              absolutePath: data.format.filename,
              audioStream
            })
          }
        }
        return res({ absolutePath: data.format.filename })
      })
    })
  }

  export namespace bitrate {
    const baseKbitrate = 384

    const toBits = (kbits: number): number => { return kbits * 8000 }

    export const aac = (bitrate: number): number => {
      switch (true) {
      case bitrate > toBits(baseKbitrate):
        return baseKbitrate
      default:
        return -1 // we interpret it as a signal to copy the audio stream as is
      }
    }

    export const mp3 = (bitrate: number): number => {
      /*
      a 192kbit/sec mp3 doesn't hold as much information as a 192kbit/sec aac.
      That's why, when using aac, we can go to lower kbit/sec. The equivalences
      made here are not made to be accurate, especially with good mp3 encoders.
      */
      switch (true) {
      case bitrate <= toBits(192):
        return 128
      case bitrate <= toBits(384):
        return 256
      default:
        return baseKbitrate
      }
    }
  }
}

/**
 * Standard profile, with variable bitrate audio and faststart.
 *
 * As for the audio, quality '5' is the highest and ensures 96-112kbps/channel
 * See https://trac.ffmpeg.org/wiki/Encode/AAC#fdk_vbr
 */
async function presetH264 (ffmpeg: ffmpeg, resolution: VideoResolution, fps: number): ffmpeg {
  let localFfmpeg = ffmpeg
    .format('mp4')
    .videoCodec('libx264')
    .outputOption('-level 3.1') // 3.1 is the minimal ressource allocation for our highest supported resolution
    .outputOption('-b_strategy 1') // NOTE: b-strategy 1 - heuristic algorythm, 16 is optimal B-frames for it
    .outputOption('-bf 16') // NOTE: Why 16: https://github.com/Chocobozzz/PeerTube/pull/774. b-strategy 2 -> B-frames<16
    .outputOption('-map_metadata -1') // strip all metadata
    .outputOption('-movflags faststart')
  const _audio = await audio.get(localFfmpeg)

  if (!_audio.audioStream) {
    return localFfmpeg.noAudio()
  }

  // we favor VBR, if a good AAC encoder is available
  if ((await checkFFmpegEncoders()).get('libfdk_aac')) {
    return localFfmpeg
      .audioCodec('libfdk_aac')
      .audioQuality(5)
  }

  // we try to reduce the ceiling bitrate by making rough correspondances of bitrates
  // of course this is far from perfect, but it might save some space in the end
  const audioCodecName = _audio.audioStream['codec_name']
  let bitrate: number
  if (audio.bitrate[audioCodecName]) {
    bitrate = audio.bitrate[audioCodecName](_audio.audioStream['bit_rate'])

    if (bitrate === -1) return localFfmpeg.audioCodec('copy')
  }

  if (bitrate !== undefined) return localFfmpeg.audioBitrate(bitrate)

  // Constrained Encoding (VBV)
  // https://slhck.info/video/2017/03/01/rate-control.html
  // https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
  const targetBitrate = getTargetBitrate(resolution, fps, VIDEO_TRANSCODING_FPS)
  localFfmpeg = localFfmpeg.outputOptions([`-maxrate ${ targetBitrate }`, `-bufsize ${ targetBitrate * 2 }`])

  // Keyframe interval of 2 seconds for faster seeking and resolution switching.
  // https://streaminglearningcenter.com/blogs/whats-the-right-keyframe-interval.html
  // https://superuser.com/a/908325
  localFfmpeg = localFfmpeg.outputOption(`-g ${ fps * 2 }`)

  return localFfmpeg
}