An efficient way to check if the file has been converted correctly is to add the converted file into Movavi Video Converter.
If there are no problems with the playback, most likely you don't have the appropriate codecs installed on your computer.
You can try using another media player that uses the codecs of its own, for instance, VLC player.
Else, please download and install the K-Lite Codec Pack Full to get all popular codecs installed on your computer.
If the converted file did not open in Movavi Video Converter, please contact us with the detailed description of the issue.
If you use an older version of Movavi Video Converter (Movavi Video Converter 14 and earler, Movavi Video Suite 12 and earlier), please try converting a video into another format other than MP4.