WebM is a Matroska subset built for browsers, holding VP8 or VP9 video, and the slowest thing to encode on this machine by a factor of ten. GIF is a palette of at most 256 colours, all-or-nothing transparency, and animation. ffmpeg sits between the two, and this page says exactly what happens to a WEBM file on the way to becoming a GIF one.
What runs when a WEBM file becomes GIF
ffmpeg held to a single thread, on a machine we rent and watch. Your WEBM file is uploaded once, ffmpeg runs once, the GIF comes back, and neither file is kept. WEBM to GIF is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the WEBM into the GIF
The aspect ratio of the WEBM. The engine scales to the smaller of 1280 pixels and the source width, and lets the height follow, rounded to an even number because encoders working in 4:2:0 refuse an odd one. A WEBM already 1280 pixels wide or narrower is not resized at all.
The running time and the order of the frames. ffmpeg re-encodes the WEBM, it does not re-cut it, so the GIF starts and ends where the WEBM did.
What WEBM to GIF costs you
The sound, entirely. GIF has no audio track at all: not a bad one, not a quiet one, none. If the point of your WEBM was what someone says in it, this is the wrong target, and converting to MP3 or keeping the WEBM is what you want instead.
Most of the colours. A GIF holds 256 of them, chosen per file, and a video holds sixteen million: ffmpeg builds a palette and maps every frame onto it. A gradient, a sky or a face lit from one side is where you see the cost, as banding.
Every pixel, one more time. The WEBM is decoded to raw frames and re-encoded as GIF, so whatever the WEBM had already lost stays lost and this pass adds its own on top. Run one file through the loop four or five times and the damage is visible without looking for it.
Any width past 1280 pixels. The engine scales the WEBM down to 1280 because encoder cost grows with pixel count: a 4K source costs about sixteen times a 1080p one, for a GIF nobody asked to be that big. Below that width nothing is touched.
Subtitle and data tracks. ffmpeg passes -sn and -dn on the way into the GIF, because most of them do not fit the container and a mux that fails on a subtitle would waste a picture that converted perfectly well.
Anything past 120 seconds of WEBM. ffprobe measures the duration before the encoder starts, and a longer WEBM comes back as a refusal in under a second rather than as a timeout four minutes later.
If a model is going to read the GIF
Nothing about WEBM to GIF helps a language model, and pretending otherwise would be a sales line rather than a fact. A GIF is pixels and sound, both expensive to read and neither of them text. If what you actually want is what is said in the WEBM, the useful move is not GIF at all: pull the audio out as MP3, which costs half a credit and comes back in about a second, and have that transcribed.
Running WEBM to GIF against the real engine with a real file, ffmpeg wrote 177,876 bytes of GIF in 0.1 seconds, machine otherwise idle. That is one WEBM file on one day and not an average, which is why the number is given together with the file that produced it.
The WEBM to GIF verdict was reached by a format signature, meaning at least four bytes unique to the format were found at the right offset. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the GIF file has anything inside it.
The same WEBM file, sent somewhere else
Other outputs the probe measured out of a WEBM file, so the cost of choosing GIF can be read against something. Sizes do not compare across engines, because each family was probed with its own WEBM witness file.
WEBM to MP3: 24,429 bytes in 0.1 seconds, verified by ffprobe.
WEBM to MP4: 46,854 bytes in 0.3 seconds, verified by ffprobe.
WEBM to WAV: 288,078 bytes in 0.1 seconds, verified by ffprobe.
WEBM to FLAC: 178,357 bytes in 0.2 seconds, verified by ffprobe.
WEBM to OGG: 9,503 bytes in 0.2 seconds, verified by ffprobe.
WEBM to M4A: 27,734 bytes in 0.2 seconds, verified by ffprobe.
Other ways into GIF, and what they measured
Among the published routes into GIF, WEBM is the third largest output of the 19 measured. The witness files differ, so this ranks the probe run and not your document.
WMV to GIF: 182,516 bytes in 0.1 seconds.
PNG to GIF: 3,512 bytes in 0.1 seconds.
MP4 to GIF: 164,004 bytes in 0.2 seconds.
WEBP to GIF: 4,744 bytes in 0.1 seconds.
PDF to GIF: 9,463 bytes in 0.1 seconds.
What we will not pretend about WEBM to GIF
A WEBM file over 150 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A WEBM to GIF run that passes 240 seconds is killed, and the ffmpeg process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
The WEBM file behind the measurement on this page was 3 seconds of 320 by 240 test pattern at 25 frames a second, with a sine wave on the audio track, built by ffmpeg for the probe itself. That is why WEBM to GIF came out at 0.1 seconds, and it is not what your file will do. The measurement proves the pair works and says almost nothing about how long yours will take.
Video is the one thing on this site that genuinely costs machine time, and the cost swings by two orders of magnitude with the encoder the container asks for: on this machine one minute of 720p source came out as AVI in 8.4 seconds and as WebM in 87, and the same minute in 1080p took 104. Expect a GIF to cost somewhere between a fraction of the WEBM running time and twice it, not the tenth of a second the probe file took.
A WEBM longer than 120 seconds is refused before any encoding starts, with an answer that names both limits, 150 MB and 120 seconds. It is not an upsell: two minutes of GIF encoding is roughly two minutes of the only machine there is, and the live traffic shares the same two cores.
WEBM to GIF is the single conversion here that is not charged at the floor rate. It costs 2 credits per minute of WEBM, every started minute counts, and because the engine refuses past 120 seconds one WEBM to GIF run can never cost more than 4 credits. The figure is on the button before you press it.
One GIF encode at a time, and that was measured before it was decided. Two simultaneous transcodes do fit in memory, about 320 MB each, but each one goes from 104 seconds to 189: this machine is short of processor, not of memory, so throughput gains ten percent while the wait doubles. WEBM to GIF therefore queues on a single slot and gives up after 25 seconds rather than piling up.
Nothing here reads what is inside the WEBM. No transcription, no scene detection, no summary: WEBM to GIF is a container and codec operation, and the GIF says exactly what the WEBM said, in a different wrapper. The picture is the whole payload.
One WEBM file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
WEBM to GIF: what people ask
What actually converts my WEBM file to GIF?
ffmpeg does it, held to a single thread, on a machine we rent and watch. Not a browser trick and not somebody else service: the WEBM file is uploaded once, ffmpeg runs once, the GIF comes back, and neither file is kept afterwards.
How long does WEBM to GIF take?
The probe measured 0.1 seconds for 177,876 bytes of GIF, on a 3 second test pattern, and that number is honest about the plumbing and useless about your file. A video target re-encodes every frame: budget somewhere between a fraction of the WEBM running time and twice it. The WEBM is refused past 120 seconds, so the worst case is bounded.
What do I lose going from WEBM to GIF?
The one to know about first: The sound, entirely. GIF has no audio track at all: not a bad one, not a quiet one, none. If the point of your WEBM was what someone says in it, this is the wrong target, and converting to MP3 or keeping the WEBM is what you want instead.
Why did my GIF come back narrower than the WEBM?
Because the engine caps every video output at 1280 pixels wide. Encoder cost grows with pixel count, and a 4K WEBM would cost about sixteen times a 1080p one on a machine that also serves everybody else. A WEBM at or below 1280 pixels comes back at its own size, untouched.
Is WEBM to GIF free?
There is a free allowance every month, and WEBM to GIF is the one conversion here that is not charged at the floor rate: 2 credits per minute of WEBM, every started minute counted, capped at 4 credits because the engine refuses past 120 seconds. Re-encoding a GIF costs real machine time, so it is priced on the time it costs. The number is shown before you press anything.