You might try using a video editor on your own computer to produce a video in the right format. For example, you could use the free and open-source Shotcut:
- Start a new Shotcut project.
- Set a sensible video option in Settings > Video Mode – HD 720p 60fps is probably fine.
- Click the ‘Playlist’ button in the toolbar.
- Drag a JPG graphic (so your video has a picture) and your MP3/WAV file into the ‘Playlist’ panel on the left. For simplicity it is probably a good idea to make sure your graphic is the right size – for HD 720p that would be 1280 x 720 pixels.
- Type Command-I to add a new video track.
- Drag the JPG from the ‘Playlist’ panel to the new video track in the ‘Timeline’ panel at the bottom of the window.
- Type Command-U to add a new audio track, and make sure it’s active by clicking on it: in the dark colour scheme it goes a kind of mustard yellow when it’s selected.
8, Drag the MP3/WAV from the ‘Playlist’ panel to the new audio track in the ‘Timeline’ panel. It may come in offset a tiny bit after 00:00, so be sure to drag the audio track to the left so it’s definitely lined up with the start of the timeline. - To make the picture last as long as the audio, zoom out using the controls in the header of the Timeline panel, then hover over the right-hand side of the image clip in the video track and drag it out to the right so that it’s the same length as the audio file.
- If you would find it useful to add timecode, activate the video track.
- Click ‘Filters’ on the toolbar at the top of the window.
- In the ‘Filters’ panel on the left, click the + button to add a new filter: in the search field type “text”, then choose the “Text” filter. By default, the text filter will use the text #timecode#, which is replaced with the timecode of the current frame during playback, which is very helpful. Position the timecode as you like in the preview window. You can use the arrow keys to move left and right frame-by-frame.
Once you’re happy, click ‘Export’ in the toolbar, and click the ‘Export File’ button at the bottom of the Export panel to export a file. All of the frame rate and resolution settings etc. should be correct. The export process takes a couple of minutes.