A GIF is usually bigger than the video it came from
Often ten times bigger, and almost nobody expects it, because everything about GIF suggests it should be the lightweight option.
The reason is age. GIF compresses each frame entirely on its own, with LZW, a scheme from 1984 that has no concept of the frame before it. Modern video compression is built on the opposite observation: consecutive frames are nearly identical, so store only what moved. A static shot of somebody talking is almost free in an MP4 and costs full price on every single frame in a GIF.
So a three second clip at 400KB as an MP4 comes out at six megabytes as a GIF. The estimate appears here before anything is encoded, so you can shorten the clip rather than wait a minute to find out.
The frame rate you ask for is usually not the one you get
This one is genuinely obscure and it explains a lot of GIFs that feel subtly wrong.
GIF stores the gap between frames in hundredths of a second. Not milliseconds. So a frame rate only works if 100 divides by it cleanly.
Fifteen frames a second needs a delay of 6.67 hundredths, which does not exist, so it becomes 7 and plays at 14.3. Twenty-four becomes 25. Thirty becomes 33.3, which is faster than you asked for. The rates that are exact are 25, 20, 10, 5, 4, 2 and 1, and the tool says which one you are getting rather than pretending.
There is a floor as well. Browsers have treated any delay under two hundredths as ten hundredths since the Netscape era, to stop malicious files pinning the processor. Ask for 60fps and you get 10fps: not slightly wrong, six times slower.
Making it smaller, in the order that works
Shorten it. By a distance the biggest lever, because length multiplies everything else. A GIF worth sending is almost always under three seconds. Find the two seconds that carry the joke and cut the rest.
Narrow it. File size goes with area, so dropping from 640 to 480 pixels wide removes nearly half the data. Most GIFs are viewed small.
Fewer frames a second. Ten is fine for most things and is a proper GIF look rather than a compromise. Five works for a slow pan.
Fewer colours, last. People reach for this first and it gains the least. Below about 64 colours banding appears in anything with a gradient in it.
APNG is better, when it is accepted
Animated PNG does everything GIF does and does it properly: full colour rather than 256 per frame, real soft transparency rather than a hard on-or-off edge, and usually a smaller file at matching quality.
Every current browser plays one. The problem is never the browser, it is everything else: plenty of platforms see a .png extension and treat it as a still, so your animation arrives as a frozen first frame.
Use APNG where you control the destination, such as your own site or a document. Use GIF for chats, forums and anywhere you are handing the file to software you have never met.
Why the tool has no watermark and no size limit
Video conversion is where free tools most often stop being free, and the reason is that most of them do the work on a server. Transcoding video costs real money in CPU time, so it gets paid for with a watermark, a queue, a size cap or a subscription.
Nothing here touches a server. Your browser already contains a video decoder, and it has for years. The frames are pulled out on your machine, the encoding happens on your machine, and the file never leaves it.
Which is also why a long clip is slow: it is your processor doing the work, not a farm of them. That is the trade, and it comes with no watermark, no cap and no account.
Common questions
Why is my GIF bigger than the video it came from?
Because GIF compresses every frame on its own, using a scheme from 1984 that knows nothing about the frame before it. Modern video compression is built almost entirely on the fact that consecutive frames are nearly identical, and it stores only what moved. So a three second clip that is 400KB as an MP4 is routinely 6MB as a GIF. That is not a fault in the conversion, it is what GIF is.
Why does my GIF play at the wrong speed?
GIF stores the delay between frames in hundredths of a second, not milliseconds. Most frame rates cannot be represented: 15fps wants 6.67 hundredths and has to become 7, which plays at 14.3fps. Ask for 30 and you get 33.3. The only rates that are exact are the ones that divide 100 cleanly, which is 25, 20, 10, 5, 4, 2 and 1. The tool tells you which you are getting.
Can I make a smooth 60fps GIF?
No, and it will play slower rather than faster if you try. Browsers have treated a frame delay under two hundredths of a second as ten hundredths since the 1990s, a rule to stop bad files pinning the processor. So asking for 60fps produces a file that plays at 10fps. Fifty is the practical ceiling and ten to fifteen is what most good GIFs use.
How do I make the file smaller?
In this order: shorten the clip, reduce the width, then reduce the frame rate, then reduce the colours. Length is by far the biggest lever because it multiplies everything else. Colours is the smallest lever, and people reach for it first. A GIF worth sending is usually under three seconds.
What is APNG and should I use it?
An animated PNG. Full colour instead of 256, proper soft transparency instead of hard-edged, and usually a smaller file at the same quality. Every current browser plays it. The catch is acceptance: some social platforms and older tools look at the .png extension and treat it as a still image. If it is going somewhere you control, APNG is the better file. If it is going into a chat or a forum, GIF is the safer one.
Why does the tool seek through the video instead of playing it?
Because playing a video to capture it takes real time, so a ten second clip would take ten seconds, and it stops completely if you switch tabs, since the frame callbacks are tied to the page being painted. Seeking to each timestamp is not tied to any of that. It also lands on the frame that was asked for rather than whichever one happened to be showing.
Is the video uploaded?
No. It is decoded by your own browser and the frames never leave the machine. There is no size limit beyond what your device can hold, no queue and no watermark, which is the usual price of the free online converters.