From Jacek Pazera:
Pazera Free MKV to MP4 Converter 64-bit is a absolutely free program that allows you to convert Matroska video files (MKV) to MP4 format.
MP4 files created by the program can be played on many portable devices (iPhone, iPod, Samsung Galaxy, Microsoft Surface, HTC, PSP) and fixed media players (WD TV, Xtreamer, Asus O!Play).
The video stream from the input file can be encoded using modern video encoders: H.264/AVC, H.265/HEVC, or the old generation, but still very popular Xvid encoder. For encoding audio streams the program uses AAC (Advanced Audio Coding) or MP3 encoder (LAME).
At default settings, the application converts files using H.264 video encoder and AAC audio encoder, and automatically selects all the encoding parameters so as to preserve the original video and audio quality. Created MP4 files will be compatible with HTML5 standard, so you can use it on your website.
The program includes a number of conversion profiles developed for the typical conversion tasks. More advanced users can customize many video and audio encoding parameters: video and audio codec, video and audio bitrate, display aspect ratio, frames per second, resolution, color conversion to grayscale or sepia, brightness, audio sampling frequency, volume and other.
The basic operation of the application is a very simple: just drag and drop MKV files into main window and click Convert button on the toolbar.