According to the official specification Chromecast (even Ultra version) doesn’t support DTS.
Once installed, simply tell it to use ffmpeg to transcode audio to mp3 (or ac3 or aac).
castnow your-wonderful-movie.mkv \ --tomp4 \ --ffmpeg-vcodec copy \ --ffmpeg-acodec mp3 \ --ffmpeg-movflags frag_keyframe+empty_moov+faststart
movflagsif you will only hear the audio and you’ll see a black screen
The only downside of transcoding is that the play / pause controls are not supported.