Videos Settings give you control of the conversion process from various video formats in to MP4.
Quality
Sets the compression level and is a compromise between video quality and file size. Start with the default setting and if the quality is not good enough raise the setting and try making the album again.
Resolution
A drop down menu lets you choose from a range of standard video resolutions such as Full HD, HD, 480p, 360p, 240p or the image bounds as set in Settings/Images. If you want a different size to any of those then you can enter values in place of $videoWidth and $videoHeight (each in two places) in ‘Use custom settings’.
Use custom settings
If you check the 'Use custom settings' box then you can configure the video conversion process, to mp4, as you want.
FFmpeg documentation
The documentation on the options available for configuring FFmpeg is available from ffmpeg.org. There is a link, FFmpeg documentation, to that page at the bottom of the custom settings.