MOV is the QuickTime container Apple designed, and the one a Mac or an iPhone writes before anything else gets to touch it. 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. ffmpeg sits between the two, and this page says exactly what happens to a MOV file on the way to becoming a WEBM one.
What runs when a MOV file becomes WEBM
ffmpeg held to a single thread, on a machine we rent and watch. Your MOV file is uploaded once, ffmpeg runs once, the WEBM comes back, and neither file is kept. MOV to WEBM 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 MOV into the WEBM
The aspect ratio of the MOV. 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 MOV already 1280 pixels wide or narrower is not resized at all.
The audio track, which travels into the WEBM alongside the picture. That is the whole difference between this pair and sending the same MOV to an audio format, where the picture is thrown away instead.
The running time and the order of the frames. ffmpeg re-encodes the MOV, it does not re-cut it, so the WEBM starts and ends where the MOV did.
What MOV to WEBM costs you
Every pixel, one more time. The MOV is decoded to raw frames and re-encoded as WEBM, so whatever the MOV 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 MOV down to 1280 because encoder cost grows with pixel count: a 4K source costs about sixteen times a 1080p one, for a WEBM 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 WEBM, 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 MOV. ffprobe measures the duration before the encoder starts, and a longer MOV 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 WEBM
Nothing about MOV to WEBM helps a language model, and pretending otherwise would be a sales line rather than a fact. A WEBM is pixels and sound, both expensive to read and neither of them text. If what you actually want is what is said in the MOV, the useful move is not WEBM 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 MOV to WEBM against the real engine with a real file, ffmpeg wrote 48,054 bytes of WEBM in 1.0 seconds, machine otherwise idle. That is one MOV file on one day and not an average, which is why the number is given together with the file that produced it.
The MOV to WEBM verdict was reached by ffprobe, meaning the container was actually demultiplexed, recognised under the right name, and carried at least one stream. 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 WEBM file has anything inside it.
The same MOV file, sent somewhere else
Other outputs the probe measured out of a MOV file, so the cost of choosing WEBM can be read against something. Sizes do not compare across engines, because each family was probed with its own MOV witness file.
MOV to GIF: 164,004 bytes in 0.1 seconds, verified by a format signature.
MOV to MP3: 24,768 bytes in 0.1 seconds, verified by ffprobe.
MOV to MP4: 45,683 bytes in 0.3 seconds, verified by ffprobe.
MOV to WAV: 266,318 bytes in 0.1 seconds, verified by ffprobe.
MOV to FLAC: 156,937 bytes in 0.1 seconds, verified by ffprobe.
MOV to OGG: 9,158 bytes in 0.2 seconds, verified by ffprobe.
Other ways into WEBM, and what they measured
Among the published routes into WEBM, MOV is the sixth largest output of the 9 measured. The witness files differ, so this ranks the probe run and not your document.
MPG to WEBM: 48,686 bytes in 1.1 seconds.
WMV to WEBM: 45,388 bytes in 1.1 seconds.
MP4 to WEBM: 48,074 bytes in 1.0 seconds.
GIF to WEBM: 49,644 bytes in 2.0 seconds.
3GP to WEBM: 48,074 bytes in 1.1 seconds.
What we will not pretend about MOV to WEBM
A MOV file over 150 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
A MOV to WEBM 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 MOV 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 MOV to WEBM came out at 1.0 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 WEBM to cost somewhere between a fraction of the MOV running time and twice it, not the tenth of a second the probe file took.
A MOV 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 WEBM encoding is roughly two minutes of the only machine there is, and the live traffic shares the same two cores.
MOV to WEBM is the single conversion here that is not charged at the floor rate. It costs 2 credits per minute of MOV, every started minute counts, and because the engine refuses past 120 seconds one MOV to WEBM run can never cost more than 4 credits. The figure is on the button before you press it.
One WEBM 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. MOV to WEBM therefore queues on a single slot and gives up after 25 seconds rather than piling up.
Nothing here reads what is inside the MOV. No transcription, no scene detection, no summary: MOV to WEBM is a container and codec operation, and the WEBM says exactly what the MOV said, in a different wrapper. The picture is the whole payload.
One MOV file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
MOV to WEBM: what people ask
What actually converts my MOV file to WEBM?
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 MOV file is uploaded once, ffmpeg runs once, the WEBM comes back, and neither file is kept afterwards.
How long does MOV to WEBM take?
The probe measured 1.0 seconds for 48,054 bytes of WEBM, 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 MOV running time and twice it. The MOV is refused past 120 seconds, so the worst case is bounded.
What do I lose going from MOV to WEBM?
The one to know about first: Every pixel, one more time. The MOV is decoded to raw frames and re-encoded as WEBM, so whatever the MOV 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.
Why did my WEBM come back narrower than the MOV?
Because the engine caps every video output at 1280 pixels wide. Encoder cost grows with pixel count, and a 4K MOV would cost about sixteen times a 1080p one on a machine that also serves everybody else. A MOV at or below 1280 pixels comes back at its own size, untouched.
Is MOV to WEBM free?
There is a free allowance every month, and MOV to WEBM is the one conversion here that is not charged at the floor rate: 2 credits per minute of MOV, every started minute counted, capped at 4 credits because the engine refuses past 120 seconds. Re-encoding a WEBM costs real machine time, so it is priced on the time it costs. The number is shown before you press anything.