From 2f71dcf8de13e5250957173c9a2efe1c5544aeb2 Mon Sep 17 00:00:00 2001 From: Felix Ableitner Date: Tue, 9 Oct 2018 18:53:16 -0500 Subject: more documentation --- shared/models/videos/video-resolution.enum.ts | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/shared/models/videos/video-resolution.enum.ts b/shared/models/videos/video-resolution.enum.ts index 4d2644cc0..c9b258921 100644 --- a/shared/models/videos/video-resolution.enum.ts +++ b/shared/models/videos/video-resolution.enum.ts @@ -43,14 +43,20 @@ export function getBaseBitrate (resolution: VideoResolution) { /** * Calculate the target bitrate based on video resolution and FPS. + * + * The calculation is based on two values: + * Bitrate at VideoTranscodingFPS.AVERAGE is always the same as + * getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always + * getBaseBitrate() * 1.4. All other values are calculated linearly + * between these two points. */ export function getTargetBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) { const baseBitrate = getBaseBitrate(resolution) // The maximum bitrate, used when fps === VideoTranscodingFPS.MAX // Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate: - // 720p: 2600 / 1750 = 1.48571428571 - // 1080p: 4400 / 3300 = 1.33333333333 + // 720p: 2600 / 1750 = 1.49 + // 1080p: 4400 / 3300 = 1.33 const maxBitrate = baseBitrate * 1.4 const maxBitrateDifference = maxBitrate - baseBitrate const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE @@ -58,7 +64,7 @@ export function getTargetBitrate (resolution: VideoResolution, fps: number, // 3300 + (x - 30) * (1320/30) // Example outputs: // 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps - // 720p10: 1283 kbps, 720p30: 1750 kbps, 720p60: 2450 + // 720p10: 1283 kbps, 720p30: 1750 kbps, 720p60: 2450 kbps return baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference) } -- cgit v1.2.3