RMVB to FLV Converter

RMVB to FLV — Two Dead Formats, and When This Still Makes Sense

Be clear about what this conversion is: it moves a video out of one obsolete container and into another. RMVB is RealNetworks' RealMedia Variable Bitrate format, whose RealVideo codec line stopped advancing after RealPlayer 9. FLV is Adobe's Flash Video container, and Adobe stopped supporting Flash Player on 31 December 2020, then began blocking Flash content from running on 12 January 2021. The short answer for almost everyone is: don't — use RMVB to MP4, which plays on phones, browsers, smart TVs and every editor. The one real reason to land on .flv is a specific legacy system — an old courseware authoring tool, a self-hosted CMS, a video appliance — that ingests FLV and refuses everything else. If that is you, the rest of this page is about doing it well.

Side-by-side: RMVB and FLV

When to Pick FLV, and When to Pick Something Else

• Pick FLV if a named legacy system requires it. Articulate- and Captivate-vintage courseware, some self-hosted video CMS installs, and a few broadcast appliances still ingest .flv and nothing newer.
• Pick FLV with the H.264 codec if that legacy system is from 2008 or later. Flash Player 9 Update 3, released 3 December 2007, added H.264 support inside FLV, and it looks considerably better than Sorenson Spark at the same bitrate.
• Pick MP4 for literally any other purpose. H.264 in an MP4 is smaller, sharper at matched size, and universally playable.
• Pick WebM if the destination is a modern web page you control and you want an open, royalty-free codec.
• Do not pick FLV expecting a smaller file. RMVB's whole reason for existing was fitting long videos into tiny downloads; re-encoding into Flash-era codecs generally makes the file bigger, not smaller.

Which Video Codec to Put Inside the FLV

Four codecs render in the Video Codec dropdown on this page, and the choice does more than change the picture — it changes which compression controls you are even offered.

The two Flash Video entries are the trap. They are screencast codecs designed for large flat areas of solid colour, and they are treated as lossless, which is why the rate-control panel collapses when you select one. Point them at a compressed movie rip and you get an enormous file that looks no better. For an RMVB of anything filmed, stay on Sorenson Spark or switch to H.264.

How to Convert RMVB to FLV

1. Upload Your RMVB File: Drag the .rmvb onto the page or click "Add Files" to browse. Batch upload works, so a folder of old RealMedia clips converts with one set of settings.
2. Pick the Video Codec and Audio Codec: Video Codec starts on FLV (Sorenson Spark) — the safest choice for genuinely old players — with H.264, Flash Video and Flash Video (v2) as alternatives. Audio Codec starts on AAC, with MP3 and Flash ADPCM (listed as ADPCM_SWF) also available; MP3 is the safest for very old Flash toolchains.
3. Set File Compression, Video Resolution and Trim (Optional): File Compression opens on Quality Preset with "Very High (Recommended)" selected; Specific file size (24 MB), Constant Bitrate (4 Mbps), Variable Bitrate, Constant Quality and Constraint Quality are the alternatives. Video resolution starts on "Keep original", which is right for a standard-definition source. Trim starts on Unchanged — switch it to Time Range to export one segment.
4. Convert and Download: Click Convert and save the .flv. Your file is uploaded over an encrypted connection, re-encoded on our servers, and both the upload and the output are deleted automatically after a few hours. No sign-up, no watermark.

Frequently Asked Questions

Should I really convert RMVB to FLV, or to MP4 instead?

For almost everyone, MP4. This route takes a near-dead 2000s RealMedia file and turns it into a dead Flash-era one; both originally depended on runtimes that no longer exist. The only honest reason to pick FLV is a specific legacy Flash-based player, CMS or e-learning tool that ingests .flv and accepts nothing else. If you want a file that plays on phones, browsers, smart TVs and modern editors, RMVB to MP4 is the answer.

Will my FLV be smaller than the original RMVB?

Almost certainly not, and it is worth setting that expectation up front. RMVB existed to make long videos tiny, and Flash-era codecs are less efficient than what RealVideo was doing. We measured this on a test clip: a 376,537-byte RealMedia source re-encoded to 553,362 bytes with Sorenson Spark at the tool's opening quality value, and to 418,366 bytes with H.264 at its opening CRF. Both are larger than the source, and neither recovered any quality — this is a lossy-to-lossy re-encode in both directions. If size matters, target a lower bitrate under File Compression, or convert to MP4 instead.

Which video and audio codec does the output use by default?

FLV (Sorenson Spark) for video and AAC for audio. Sorenson Spark is a proprietary H.263 variant carrying the FourCC FLV1, and every Flash Player from version 6 onwards could decode it, which makes it the safest default when you do not know what will read the file. AAC is the modern choice for the audio side; MP3 has broader reach across older Flash toolchains, and the Flash ADPCM entry, listed as ADPCM_SWF, is there for the very oldest.

Why did most of the compression settings vanish when I changed the codec?

Because you selected Flash Video or Flash Video (v2). Those are the Flash Screen Video codecs — screencast formats built from zlib-compressed bitmap tiles — and they are handled as lossless codecs, so Quality Preset, Specific file size, Constant Bitrate, Variable Bitrate and Constraint Quality are all hidden and only Constant Quality remains. That is correct behaviour for a lossless codec, but it means those two options are the wrong pick for filmed content. Switch back to FLV (Sorenson Spark) or H.264 and the full panel returns.

The Constant Quality slider shows a different range depending on the codec. Why?

Because the two codecs use different quality scales and the control adapts. With FLV (Sorenson Spark) selected it is an MPEG-style quantizer running 1 to 31, opening at 5, where lower is better and the practical good range is narrow. Switch Video Codec to H.264 and the same control becomes a genuine 0–51 CRF scale opening at 23. Carrying a number across from one to the other will give you a badly wrong result — 23 is a reasonable H.264 CRF but a very poor Sorenson Spark quantizer.

Can I still play an FLV now that Flash Player is gone?

Yes. The web delivery pipeline is dead, but the file is not unreadable. Adobe ended Flash Player support on 31 December 2020 and started blocking Flash content on 12 January 2021, so no browser plays .flv natively and no modern site serves it — but VLC, MPV and ffmpeg still decode the container fine, because those never relied on the Flash plug-in. This is the key difference from .swf: an FLV is plain audio and video you can replay and re-convert, whereas a SWF was an application with no runtime left to run it.

Will the frame size be changed or snapped to a fixed value?

No. Sorenson Spark inside FLV accepts arbitrary frame dimensions — we confirmed this by encoding a deliberately awkward 853 × 479 frame, which came back at exactly 853 × 479. That is worth knowing because some other H.263-derived targets do force the picture into a short list of legal sizes. Here, "Keep original" really does keep the original, and the Preset Resolutions list sets height with width following the source aspect.

Why won't my RMVB file convert at all — is it protected?

Some commercial and subscription RealMedia files carry RealNetworks rights management, which blocks decoding in every tool rather than just this one; there is no setting that works around it. Unprotected .rmvb files convert normally. If a file fails and you know it is not rights-managed, it is far more likely truncated or corrupted — very common for clips pulled over long-dead file-sharing networks. Open it in VLC first: if VLC cannot play it end to end, re-download a clean copy before trying again. Going the other direction, from an old Flash file back to RealMedia, is covered by FLV to RMVB.