Use GIF when the destination expects an animated image and compatibility matters more than compression efficiency. Use MP4 when the destination supports video and you want better compression options and playback controls.
The same reaction can be distributed in both formats, but a GIF URL and an MP4 URL are not interchangeable in application code.
Understand what changes
GIF uses a limited color palette and supports frame-based animation without audio. MP4 is a container commonly used with video codecs that can compress photographic motion more efficiently. Actual file size depends on the source, dimensions, duration, frame rate, and encoding settings.
Do not promise a fixed percentage reduction. Compare the actual renditions at the display size and quality your product needs. A short simple animation can behave differently from a detailed movie clip.
MDN’s media-format guides explain the distinction between image formats, containers, and codecs.
Match the destination
A normal image slot can display GIF but cannot render MP4 just because the URL is assigned to src. A video element needs a video source. Email, chat, document, and presentation tools each have their own supported insertion and playback behavior.
For web previews, a video element can provide controls and a poster image. Muted inline playback may be appropriate for a preview, but autoplay is still subject to browser policy and user preferences. See MDN’s video reference.
Keep motion optional
Switching to video can make pause behavior easier to implement, but autoplaying every card remains distracting. Start with a static poster for reduced-motion users and preserve a manual play control.
For a GIF displayed through an image element, provide a static alternative or a separate control that replaces the animated source. The accessibility guide covers the design requirements.
Use returned formats, not invented URLs
GIFs.so returns a GIF URL and a nullable MP4 URL. Check whether the MP4 exists before offering it. Never generate a video URL by replacing the filename extension of a GIF.
The integration guide documents those fields. If you need to reduce the size of media you are authorized to modify, follow the compression guide and test the final file in its real destination.