Actually... I removed the meme version and installed the latest version back. You know what, it plays my 1080p/DTS files with audio downmixing perfectly! Not sure what's happened but yay for myself.

Let me describe my buffering symptom of the latest version.

If playing a mkv/h264/aac video without any transcoding the app works perfectly. If playing a video with DTS audio and set to downmix, the app starts to buffer. If set to "AC3" then there will be no sound (chromecast can't bitstream DTS, my TV can't decode it either), but the video plays perfectly. There doesn't seem to be any transcoding happening. In stereo mode, even if I lower the quality of the video (orginal 1080p, set to 720p) it still buffers heavily. But with no tanscoding, it plays 1080p perfectly.

I've also tried the meme/1.3 version posted above. It plays everything perfectly, even with DTS downmixing.

Hope my information will help you to fix the problem.