If your Roku device (like the Roku Ultra or certain Roku TVs) has a USB port, you can play MKV files directly from a flash drive.
: Plug your USB drive into the Roku. Open Roku Media Player , select your device, and navigate to the video. Enable Text/Captions : roku play mkv
AAC, AC3 (Dolby Digital), EAC3 (Dolby Digital Plus), DTS (pass-through only), MP3, FLAC, and PCM. If your Roku device (like the Roku Ultra