AVI is a Microsoft container from 1992, still readable everywhere and unable to carry most of what video learned afterwards. FLV is the Flash Video container, orphaned the day the plugin that gave it a name was switched off. ffmpeg sits between the two, and this page says exactly what happens to an AVI file on the way to becoming an FLV one.
What runs when an AVI file becomes FLV
ffmpeg held to a single thread, on a machine we rent and watch. Your AVI file is uploaded once, ffmpeg runs once, the FLV comes back, and neither file is kept. AVI to FLV 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 AVI into the FLV
The aspect ratio of the AVI. 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. An AVI already 1280 pixels wide or narrower is not resized at all.
The audio track, which travels into the FLV alongside the picture. That is the whole difference between this pair and sending the same AVI to an audio format, where the picture is thrown away instead.
The running time and the order of the frames. ffmpeg re-encodes the AVI, it does not re-cut it, so the FLV starts and ends where the AVI did.
What AVI to FLV costs you
Every pixel, one more time. The AVI is decoded to raw frames and re-encoded as FLV, so whatever the AVI 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 AVI down to 1280 because encoder cost grows with pixel count: a 4K source costs about sixteen times a 1080p one, for an FLV 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 FLV, 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 AVI. ffprobe measures the duration before the encoder starts, and a longer AVI 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 FLV
Nothing about AVI to FLV helps a language model, and pretending otherwise would be a sales line rather than a fact. An FLV is pixels and sound, both expensive to read and neither of them text. If what you actually want is what is said in the AVI, the useful move is not FLV 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 AVI to FLV against the real engine with a real file, ffmpeg wrote 165,557 bytes of FLV in 0.2 seconds, machine otherwise idle. That is one AVI file on one day and not an average, which is why the number is given together with the file that produced it.
The AVI to FLV 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 FLV file has anything inside it.
The same AVI file, sent somewhere else
Other outputs the probe measured out of an AVI file, so the cost of choosing FLV can be read against something. Sizes do not compare across engines, because each family was probed with its own AVI witness file.
AVI to GIF: 173,720 bytes in 0.2 seconds, verified by a format signature.
AVI to MP3: 24,711 bytes in 0.2 seconds, verified by ffprobe.
AVI to MP4: 48,231 bytes in 0.3 seconds, verified by ffprobe.
AVI to WAV: 267,342 bytes in 0.1 seconds, verified by ffprobe.
AVI to FLAC: 156,801 bytes in 0.1 seconds, verified by ffprobe.
AVI to OGG: 9,164 bytes in 0.1 seconds, verified by ffprobe.
Other ways into FLV, and what they measured
Among the published routes into FLV, AVI is the ninth largest output of the 9 measured. The witness files differ, so this ranks the probe run and not your document.
GIF to FLV: 174,055 bytes in 0.2 seconds.
MKV to FLV: 177,042 bytes in 0.2 seconds.
MOV to FLV: 177,109 bytes in 0.2 seconds.
MPG to FLV: 177,342 bytes in 0.2 seconds.
WEBM to FLV: 169,113 bytes in 0.2 seconds.
What we will not pretend about AVI to FLV
An AVI file over 150 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
An AVI to FLV 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 AVI 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 AVI to FLV came out at 0.2 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 an FLV to cost somewhere between a fraction of the AVI running time and twice it, not the tenth of a second the probe file took.
An AVI 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 FLV encoding is roughly two minutes of the only machine there is, and the live traffic shares the same two cores.
AVI to FLV is the single conversion here that is not charged at the floor rate. It costs 2 credits per minute of AVI, every started minute counts, and because the engine refuses past 120 seconds one AVI to FLV run can never cost more than 4 credits. The figure is on the button before you press it.
One FLV 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. AVI to FLV therefore queues on a single slot and gives up after 25 seconds rather than piling up.
Nothing here reads what is inside the AVI. No transcription, no scene detection, no summary: AVI to FLV is a container and codec operation, and the FLV says exactly what the AVI said, in a different wrapper. The picture is the whole payload.
One AVI file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
AVI to FLV: what people ask
What actually converts my AVI file to FLV?
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 AVI file is uploaded once, ffmpeg runs once, the FLV comes back, and neither file is kept afterwards.
How long does AVI to FLV take?
The probe measured 0.2 seconds for 165,557 bytes of FLV, 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 AVI running time and twice it. The AVI is refused past 120 seconds, so the worst case is bounded.
What do I lose going from AVI to FLV?
The one to know about first: Every pixel, one more time. The AVI is decoded to raw frames and re-encoded as FLV, so whatever the AVI 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 FLV come back narrower than the AVI?
Because the engine caps every video output at 1280 pixels wide. Encoder cost grows with pixel count, and a 4K AVI would cost about sixteen times a 1080p one on a machine that also serves everybody else. An AVI at or below 1280 pixels comes back at its own size, untouched.
Is AVI to FLV free?
There is a free allowance every month, and AVI to FLV is the one conversion here that is not charged at the floor rate: 2 credits per minute of AVI, every started minute counted, capped at 4 credits because the engine refuses past 120 seconds. Re-encoding an FLV costs real machine time, so it is priced on the time it costs. The number is shown before you press anything.