I can confirm this is an issue with Android device as well.
Its been reported here as well. Audio transcode causing video transcode
Any android based device I own transcodes the audio and the video for files containing EAC3 audio. That includes my Pixel, my Nvidia Shields, and my Fire-tv.
Roku does not have this issue, nore is the issue present if I cast to my Shield. Hell its not even present if I cast to my Google Home Hub display. All of these use direct play for audio and video.
