Hi, I'm having some issues with the new Chromecast and 24 Hz / 50 Hz modes.
I own a 1080p Sony TV with no frame rate interpolation or frame rate adaptation of 24p media to 60 Hz that newer tvs have.
I was having issues with the new CC at 50 Hz not playing 25p european media smoothly in Amazon Prime Video and some other apps, playback having quite visible judder and frame skips. The same thing happened sometimes playing 24p media in 24 Hz mode.
After some experimentation, I have found that in order to have smooth playback in these apps, I have to select the adequate video mode (1080p 24 Hz or 50 Hz) to the media I want to watch, and reboot. Once rebooted, this media then plays smoothly with no judder. Every time I want to watch media in these apps with a different frame rate than the one that was configured at boot, I have to change the video mode to match the media and then reboot, then it plays smoothly.
However, this doesn't happen with Netflix app. Netflix doesn't require a reboot after changing video mode in order to have smooth playback. In Netflix after just changing video mode the playback of corresponding media is smooth.
(There is however a known separate issue of new CC 24 Hz video mode being 23,976 Hz instead, so that true 24p media such as Netflix originals drop a frame every 41 seconds).
This is a bug in the new Chromecast that is not present in other Android TV boxes and I hope is fixed in future updates. The fact that it happens in some apps but not in others such as Netflix makes me guess it may be due to different ways of handling media playback internally in these apps.
Aside from fixing this bug, I hope automatic frame rate selection such as the one present in Apple TV is implemented in the future. It's quite uncomfortable having to change video mode manually all the time in order to have smooth playback.