In fact, Roku supports 2ch AAC, 2ch MP3, pass-through AC3, and DTS. If your MKV videos use AAC 5.1 surround sound, the video will play normally yet there is no sound in Roku media player. In such cases, you can convert the MKV with 5.1 surround sound AAC to 5.1 Dolby Digital AC3 as Roku can easily stream pass-through AC3 to an HDTV. Therefore, a good Roku MKV converter is necessary. WonderFox HD Video Converter Factory Pro offers conversions between 500+ video & audio formats and popular devices. It can help you to solve the problem with ease.