Basically to get as close as possible to a smooth video playback experience with various types of Video content without having to reconfigure the Android GUI display refresh rate all the time.
You are limited to 24, 50 and 60Hz Output refresh rates with AMlogic and Rockchip devices. 60Hz only on the Amazon Fire TV + Stick and even the new NVIDIA Shield believe it or not. Although Frame rate switching is a built in feature of the new Android 5.0 Lollipop OS.
fps = Frames per second
Most movies display at 23.976fps (24p)
Most TV in Europe / UK / Oz / NZ is 25, 30, 29.97 or 50fps
TV in the States is usually 29.97 or 30fps
SPMC or Kodi Isengard actually has support already built into it to Frequency switch to the closest matching valid TV display output refresh rate based on the Frame Rate of the source video content being played. This works with AMlogic SoC's and some Rockchip devices.
See the link below to get details of the correct permission to set for SPMC and Kodi Isengard Auto-Frame rate setup:
http://spmc.semperpax.com/
You also have to enable:
Kodi > Settings > System > Video > Playback > Adjust display refresh rate to match video > On Start/Stop
If the Frequency switcher were not available then you have to manually configure the Android desktop GUI refresh rate every time, and you end up with results like this.... (Based on an AMlogic S805 SoC system)
Quote:Sync playback to Display set in Kodi settings with
- A/V Sync Method - Resample Audio > Will not work in Android
Kodi Refresh Rate set at 60Hz....
23.976fps (24p) (most movies + Netflix, Amazon Prime etc) will employ a 3:2 pulldown technique to playback video. This will result in slight judder of the video, noticable by some people when the camera pans left<->right in a scene.
Kodi Refresh Rate set at 50Hz...
24p video - judder even worse on most devices.
Kodi Refresh Rate set at 24 Hz.... (playback now also on a capable 24p TV)
24p video - buttery smooth playback until every 41 seconds when there will be a slight video hiccup.
Some say the hiccup can be virtually eliminated by turning on a Motion Smoothing or similar setting on their TV's.
Results are mixed however between various brands of TV. If that is the case leave the Android GUI display refresh rate set at 60 Hz and disable Auto refresh rate switching in Isengard.
Clear as Mud ?