Click the “Choose Files” button to select your MKV files. Click the “Convert to FLV” button to start the conversion. When the status change to “Done” click the “Download FLV” button. Click the “Choose Files” button to select your M4V files. Click the “Convert to MKV” button to start the conversion. When the status change to “Done” click the “Download MKV” button. MKV to MP4, Online Converter - Convert Video, Audio, Image, PDF - OnlineConvert.com, Online Convert files like pdf, images, video, documents, audio and more to other formats with this free and fast online converter. Step 2. Hit Choose Files and select the original video that you'd like to convert its format from MKV to MOV. Step 3. Hit the gear icon to open the Settings panel. Herein, you can modify the codec/frame rate, trim the video length, change the orientation, etc. Hit OK to confirm the adjustments. Step 4. Remux your File to MKV. To use FFmpeg, you’ll call the binary from the command line and give it various arguments or parameters to tell it what to do. In our case, we’re going to copy all streams in the file and output to an MKV container, so the command will generally look like: /path/to/ffmpeg -i /path/to/inputfile.mp4 -c copy -map 0 Converting MKV to MP4. So I am trying to convert a really long video from MKV to MP4. I tried this command first which is supposed to be the fastest way to convert mkv to mp4. [mp4 @ 0x7fffe98ae500] track 1: codec frame size is not set [mp4 @ 0x7fffe98ae500] opus in MP4 support is experimental, add '-strict -2' if you want to use it. How to Convert MP4 to MKV? Click the “Choose Files” button to select your MP4 files. Click the “Convert to MKV” button to start the conversion. When the status change to “Done” click the “Download MKV” button How to convert MKV to MP4 online. 1 To start converting, simply upload one or more MKV videos to the converter area. 2 Next, use the video conversion settings and click the "Convert" button. 3 After the conversion is complete, you can download your video files in MP4 format. Follow the steps below to know how to convert MP4 to MKV online with this converter. Step 1: Get your MP4 ready for upload on the Online-Convert.COM. Just click the “Choose File” interface or enter the URL of the video file that you want to convert to MKV. Step 2: Select the output format “MKV.”. Click the Choose Other Profile from the drop-down menu, and you will see Format and Device options in the profile library. Select one format or device as you like. If you have higher requests regarding the output video, set all the video and audio parameters via the Advanced Settings. 3. Start to convert video. 92Tp7.