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Need help?FLV to FLV — What Actually Changes
Keeping the .flv extension while changing what is inside it is the whole point of this page. The FLV container outlived the plugin that made it famous: Adobe stopped supporting Flash Player on December 31, 2020 and began blocking Flash content from running in it on January 12, 2021, yet FLV files are still produced by older OBS Studio configurations and still sitting in archives by the thousand. A same-format pass lets you replace an ancient Sorenson Spark stream with H.264 inside the same wrapper, re-cut the recording, or force a whole batch of screen captures onto one resolution.
Every job here is a full re-encode on our servers — the file is decoded and encoded again, never copied through — so treat it as a one-time conversion rather than something to repeat. Free, no sign-up, no watermark; uploads travel over an encrypted connection and are deleted automatically after a few hours.
The Four Video Codecs in the FLV Dropdown
Which codec you pick changes not only the output but which File Compression controls even appear. This is the single most useful thing to know about this page.
| Codec in dropdown | What it is | File Compression controls you get | Sensible use |
|---|---|---|---|
| FLV (default) | Sorenson Spark, the H.263 variant early YouTube used | Quality Preset, Specific file size, Constant Bitrate, Constant Quality, Constraint Quality — Constant Quality is a 1-31 qscale opening at 5 | Maximum compatibility with legacy FLV players and flv.js |
| H.264 | The same AVC codec MP4 uses, legal inside FLV since Flash Player 9 | The full set, with a true CRF slider on a 16-51 scale opening at 23 | Best quality per byte by a wide margin. Pick this unless something specific forbids it |
| Flash Video | Screen Video (flashsv), a lossless screencast codec |
Everything collapses to Constant Quality only — presets, bitrate modes, file-size targeting and Constraint Quality all disappear | Screen recordings of text and UI, where lossless matters more than size |
| Flash Video (v2) | Screen Video 2 (flashsv2), the improved screencast codec |
Same collapse to Constant Quality only | As above, slightly better compression than v1 |
Note the omission: unlike most video targets on this site, FLV does not offer a Variable Bitrate mode. Constant Bitrate is the only explicit bitrate control here.
How to Re-encode an FLV File
- Upload Your FLV Files: Drag and drop, or click "+ Add Files". Free uploads are limited to 400 MB per file (1 GB on Basic, 4 GB on Pro); batches share one set of settings.
- Pick a Video Codec: The dropdown opens on FLV. Switching to H.264 is the single change that most improves a legacy file — the same picture at a fraction of the bitrate — and it unlocks the CRF slider. The two Flash Video entries are lossless screencast codecs and deliberately strip the rest of the compression panel.
- Pick an Audio Codec: AAC is preselected. MP3 is the compatibility choice for very old playback stacks, and ADPCM_SWF exists for Flash-era authoring workflows. There are only these three; FLV's audio tag format does not admit more.
- Resize, Trim, then Convert: Video resolution starts on Keep original. Resolution Percentage, a height-based Preset from 4320p to 144p, a Width or Height with the aspect ratio locked, or an exact Width x Height are all available. Trim takes a start time plus a duration. Click Convert and download individually or as a ZIP.
What the FLV Container Can and Cannot Carry
| Property | FLV |
|---|---|
| Origin | Macromedia, 2003; Adobe from 2005 |
| Video codecs legal inside it | Sorenson Spark (H.263), On2 VP6, Screen Video 1/2, H.264 |
| Audio codecs legal inside it | MP3, AAC, Nellymoser, ADPCM, Speex |
| Subtitles | None. There is no soft-subtitle track type |
| Chapters | None |
| Multiple audio tracks | Not in practice; players expect one |
| Metadata | An onMetaData script tag only — no rich tagging |
| Browser playback today | None natively. Requires a JavaScript wrapper such as flv.js plus Media Source Extensions |
| Desktop playback today | VLC, MPV and PotPlayer still decode it |
If the file needs to survive as something normal people can open, the honest advice is to leave the container behind: FLV to MP4 writes H.264 into a wrapper every browser, phone, TV and editor accepts. Staying on FLV makes sense when a legacy player, a media server ingest path, or an archive checksum manifest demands the extension.
Frequently Asked Questions
Will switching the codec to H.264 make my FLV smaller?
Usually by a large margin, yes. Sorenson Spark is an H.263 derivative from the late 1990s; H.264 delivers similar perceptual quality at roughly a third to a half of the bitrate. The file stays a .flv and any player that handled Flash-era H.264 video — which includes flv.js and VLC — reads it. The caveat is the usual one: the encode is fresh, so you cannot recover detail the original Spark encode already discarded.
Why did all the compression options disappear when I chose Flash Video?
Because Screen Video and Screen Video 2 are lossless codecs. There is nothing for a quality preset, a bitrate cap or a target file size to negotiate, so the interface hides those modes and leaves Constant Quality. That is correct behaviour rather than a fault, but it does mean the output size is entirely determined by how much your screen recording actually changes frame to frame.
Does FLV to FLV lose quality?
Yes. There is no stream-copy path on our servers — the video is decoded to frames and encoded again on every job. On the default FLV codec that is a second pass of lossy H.263-style compression. If you only need to trim a clip and want no re-encode penalty at all, no online converter can offer that; a local tool doing a stream copy is the only way, and it cannot change codec, resolution or audio while doing it.
Can I keep my FLV playable in a browser?
Not directly. No current browser has a native FLV decoder, and the <video> element will not touch one. The two workable routes are shipping flv.js alongside the file, which needs Media Source Extensions and a fair amount of JavaScript, or converting to MP4, which every current browser plays natively. For anything public-facing, the second route is the one that will still work in five years.
What happened to the Variable Bitrate option I see on other pages?
It is not offered for FLV. The visible File Compression modes on this page are Quality Preset, Specific file size, Constant Bitrate, Constant Quality and Constraint Quality. If you need a rate range with a floor and ceiling, use Constraint Quality, which pairs a quality value with a maximum bitrate cap.
My OBS recordings are FLV. Should I convert them or change OBS?
Both. OBS historically defaulted to FLV because a crash mid-recording leaves an FLV playable while an unfinalised MP4 can be unreadable; modern OBS builds solve that with fragmented MP4 and MKV recording options, so change the setting for future captures. For the archive you already have, one pass to H.264 — inside FLV if you must keep the name, into MP4 if you do not — is enough.
Does the audio survive a same-format conversion?
The track survives, but it is re-encoded rather than passed through. AAC in gives AAC out at a fresh bitrate by default; you can force MP3 instead if an old decoder is choking on AAC. What does not survive is anything exotic — Nellymoser and Speex tracks in a legacy FLV are decoded and re-encoded into one of the three codecs this page offers.
Is there a faster way to just make the file smaller?
Yes — Compress FLV is built for exactly that and opens on a "Target file size (%)" slider, a control this converter hides. Use it when size is the only variable you care about. Come back here when you need to change the codec, the audio, the resolution or the running time as well.
How long do my files stay on the server?
Uploads and their outputs are deleted automatically after a few hours. Nothing is shared, published or indexed in the meantime, and no account or email address is required to use the tool.