How to Convert FLV to MP4? Click the “Choose Files” button to select your FLV files.; Click the “Convert to MP4” button to start the conversion.; When the status change to “Done” click the “Download MP4” button; Best Quality. We use both open source and custom software to make sure our conversions are of the highest quality. 2. Set target video format, bitrate, aspect, frame size and frame rate. The target video format can be MP4, AVI, FLV, MPG, MKV, WMV, M2TS, WEBM, ASF, MOV, M4V, RM, VOB, OGV or GIF. 3. Click "Convert Now!" button to start batch conversion. It will automatically retry another server if one failed, please be patient while converting.