Choose MP4 when the picture matters
MP4 is the sensible choice for tutorials, demonstrations, talks with slides, performances and anything else where the visual part carries meaning. It keeps video and audio together in one widely supported file.
Choose MP3 when you only need sound
MP3 removes the video and keeps an audio track. It suits spoken interviews, permitted music, lectures and listening in the car. Since there are no video frames to store, the finished file is usually much smaller.
Quality works differently
An MP4 quality such as 720p or 1080p describes the number of vertical pixels in the picture. An MP3 setting such as 128 or 192 kbps describes how much audio data is used each second. These numbers are not directly comparable.
A higher setting cannot restore missing detail
Selecting 320 kbps does not improve audio that started with less detail. In the same way, choosing a larger video resolution cannot create a picture quality that the original video does not offer.
A practical recommendation
Pick MP4 at 720p for a balanced everyday video. Choose 1080p when text or fine detail matters. For spoken audio, 128 kbps is often enough. For music or mixed material, 192 kbps is a useful balance between quality and size.
Helpful things to remember
For most people, MP4 is the best format for saving a permitted YouTube video because it keeps the picture and sound together. MP3 is better when you only want the audio and prefer a file that works in music players, car systems and podcast apps.
Before downloading, think about how you will use the file. A 720p MP4 is a practical everyday choice, while 1080p can help with small text and visual detail. For MP3 audio, 192 kbps offers a useful balance for many listeners.