1 files changed, 44 insertions, 0 deletions

diff --git a/server/helpers/ffmpeg/framerate.ts b/server/helpers/ffmpeg/framerate.ts
new file mode 100644
index 000000000..18cb0e0e2
--- /dev/null
+++ b/server/helpers/ffmpeg/framerate.ts
@@ -0,0 +1,44 @@
+import { VIDEO_TRANSCODING_FPS } from '@server/initializers/constants'
+import { VideoResolution } from '@shared/models'
+
+export function computeOutputFPS (options: {
+  inputFPS: number
+  resolution: VideoResolution
+}) {
+  const { resolution } = options
+
+  let fps = options.inputFPS
+
+  if (
+    // On small/medium resolutions, limit FPS
+    resolution !== undefined &&
+    resolution < VIDEO_TRANSCODING_FPS.KEEP_ORIGIN_FPS_RESOLUTION_MIN &&
+    fps > VIDEO_TRANSCODING_FPS.AVERAGE
+  ) {
+    // Get closest standard framerate by modulo: downsampling has to be done to a divisor of the nominal fps value
+    fps = getClosestFramerateStandard({ fps, type: 'STANDARD' })
+  }
+
+  // Hard FPS limits
+  if (fps > VIDEO_TRANSCODING_FPS.MAX) fps = getClosestFramerateStandard({ fps, type: 'HD_STANDARD' })
+
+  if (fps < VIDEO_TRANSCODING_FPS.MIN) {
+    throw new Error(`Cannot compute FPS because ${fps} is lower than our minimum value ${VIDEO_TRANSCODING_FPS.MIN}`)
+  }
+
+  return fps
+}
+
+// ---------------------------------------------------------------------------
+// Private
+// ---------------------------------------------------------------------------
+
+function getClosestFramerateStandard (options: {
+  fps: number
+  type: 'HD_STANDARD' | 'STANDARD'
+}) {
+  const { fps, type } = options
+
+  return VIDEO_TRANSCODING_FPS[type].slice(0)
+                                    .sort((a, b) => fps % a - fps % b)[0]
+}