Chromecast (2ed) direct play of videos with multiple audio streams

[JosteinG 0]

Streaming (without transcoding) a largish (2.2GB) MP4-file from the android app causes significant lagging when changing among several audio stream (5 AAC streams), while streaming an MKV-file with the same video- and audio settings is unproblematic (as long as I've started emby on the chromecast beforehand).

The files were encoded on Handbrake (1.11.2). Preset Chromecast 1080p30, only with more audio streams added. 

Emby server is running on an rpi 4, transcoding disabled for my user.

What is the reason? Is it fixable?