If your Amazon Fire TV or Fire TV Stick has received the 126.96.36.199 software update, you may be experiencing poor video playback within MrMC, Kodi, and SPMC. The developer of MrMC has emailed me letting me know that the updated version of Fire OS does not handle switching the video output to a 24Hz refresh rate correctly. This is a feature videophiles use to achieve perfect 1-to-1 synchronization between the frames in a video and the rate at which the display updates, but with software version 188.8.131.52, it results in jerky stuttering video.
Amazon only supports playing video at 50p and 60p with their own Amazon Video streams, but they have added the option for 3rd-party developers to manage the device’s video refresh rate. MrMC was the first app to support the option to switch refresh rates on Fire TV devices so they match the frame rate fo the video being played. Kodi and SPMC later adopted the feature from MrMC’s open source code.
One of MrMC’s developers, Scott Davilla, tells me the problem lies within the Fire TV’s kernel. Playing a video while the device is outputting video at 24Hz results in VSYNC errors constantly being reported by the Fire TV’s kernel. He has verified the issue, which was first reported by a user on the MrMC forum, on a 1st-gen Fire TV, but is unsure if it also exists on other Fire TV and/or Fire TV Stick models.
If you don’t want to lose smooth 24p video playback, your only option for now is to block software updates. All devices are performing fine with 50p and 60p playback, which is what most people use. Since only a relatively small percentage of Fire TV owners use 24p playback, this issue may not be a top priority for Amazon, so we may not see it fixed until the next scheduled software update.