CONVERT.
Common format conversions, each with what actually changes and what it costs you. All free, no watermark, up to 1 GB per file.
Video
MOV to MP4
MOV is Apple's QuickTime container, so it is what you get from an iPhone, an iPad, or anything exported out of Final Cut.
WEBM to MP4
WEBM is a web-native format, so it is what you end up with after downloading from a browser-based tool or saving something a website served you.
MKV to MP4
MKV is the flexible container recording software reaches for, because it survives a crash mid-recording instead of corrupting the whole file.
AVI to MP4
AVI is a container from the 1990s that refuses to die, so it turns up in old archives, old camera footage, and anything that has been sitting on a hard drive for a decade.
FLV to MP4
FLV is the Flash video format, and Flash has been dead since 2020.
MP4 to WEBM
This is the one that runs the other way, and it is almost always for a website.
MP4 to GIF
GIFs autoplay silently, loop forever, and paste into places that will not take a video at all: issue trackers, chat apps, forum posts, documentation.
MOV to GIF
This is the screen-recording route.
Audio
MP4 to MP3
Sometimes only the sound matters: pulling the audio from an interview to transcribe it, lifting a voiceover out of a finished edit, or turning a video into something you can listen to without watching.
WAV to MP3
WAV is uncompressed, which is exactly what you want while recording and editing, and completely impractical afterwards.
M4A to MP3
M4A is what Apple devices produce: voice memos, GarageBand bounces, audio pulled from Apple software.
FLAC to MP3
FLAC is lossless, so it is what archives and serious music collections use.
Images
HEIC to JPG
HEIC is the format iPhones have shot in by default for years.
PNG to JPG
PNG is the right format for graphics, screenshots and anything with text or transparency.
PNG to WEBP
If the PNG is going on a website, WEBP is simply the better format: meaningfully smaller at the same quality, and supported by every current browser.
JPG to WEBP
The same logic applied to photographs.
WEBP to PNG
This is the direction people take when a tool refuses WEBP.
WEBP to JPG
The same compatibility problem, but for photographs, where PNG would produce a needlessly huge file.