+
+/**
+ * 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 (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
+ let localCommand = await presetH264(command, input, resolution, fps)
+
+ localCommand = localCommand.outputOption('-preset:v veryfast')
+
+ /*
+ 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,
+ although not to the point of a livestream where there is a hard
+ constraint on the frames per second to be encoded.
+ */
+
+ return localCommand
+}
+
+/**
+ * A toolbox to play with audio
+ */
+namespace audio {
+ export const get = (option: string) => {
+ // 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) => {
+
+ function parseFfprobe (err: any, data: ffmpeg.FfprobeData) {
+ 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 })
+ }
+
+ return ffmpeg.ffprobe(option, parseFfprobe)
+ })
+ }
+
+ 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 (command: ffmpeg.FfmpegCommand, input: string, resolution: VideoResolution, fps?: number) {
+ let localCommand = command
+ .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('-pix_fmt yuv420p') // allows import of source material with incompatible pixel formats (e.g. MJPEG video)
+ .outputOption('-map_metadata -1') // strip all metadata
+ .outputOption('-movflags faststart')
+
+ const parsedAudio = await audio.get(input)
+
+ if (!parsedAudio.audioStream) {
+ localCommand = localCommand.noAudio()
+ } else if ((await checkFFmpegEncoders()).get('libfdk_aac')) { // we favor VBR, if a good AAC encoder is available
+ localCommand = localCommand
+ .audioCodec('libfdk_aac')
+ .audioQuality(5)
+ } else {
+ // we try to reduce the ceiling bitrate by making rough matches of bitrates
+ // of course this is far from perfect, but it might save some space in the end
+ localCommand = localCommand.audioCodec('aac')
+
+ const audioCodecName = parsedAudio.audioStream[ 'codec_name' ]
+
+ if (audio.bitrate[ audioCodecName ]) {
+ const bitrate = audio.bitrate[ audioCodecName ](parsedAudio.audioStream[ 'bit_rate' ])
+ if (bitrate !== undefined && bitrate !== -1) localCommand = localCommand.audioBitrate(bitrate)
+ }
+ }
+
+ if (fps) {
+ // 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)
+ localCommand = localCommand.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
+ localCommand = localCommand.outputOption(`-g ${fps * 2}`)
+ }
+
+ return localCommand
+}
+
+async function presetCopy (command: ffmpeg.FfmpegCommand): Promise<ffmpeg.FfmpegCommand> {
+ return command
+ .format('mp4')
+ .videoCodec('copy')
+ .audioCodec('copy')
+}