M2TS to FLV Converter

Converting M2TS to FLV: What This Tutorial Covers

This walks through turning an AVCHD or Blu-ray .m2ts clip into a Flash Video .flv file, and it is written for one specific reader: someone whose un-migrated Flash-era courseware, learning management system, or CMS ingest still demands .flv and rejects everything else. There is one decision on this page that determines whether the result is usable or a blurry, oversized mess — the Video Codec dropdown — so the walk-through below spends most of its time there. If a Flash-era system is not what you are feeding, M2TS to MP4 is the tool you actually want.

How to Convert M2TS to FLV

1. Upload Your M2TS File: Drag your .m2ts clip onto the page or click "+ Add Files". This page accepts the .m2ts extension only — camcorder cards that write .MTS go to MTS to FLV. Batch upload works, and one set of settings applies to the whole queue.
2. Choose the Video Codec: The dropdown offers FLV (Sorenson Spark, the default), H.264, Flash Video, and Flash Video (v2). Only the first two are sensible for camera footage; the walk-through below explains why the other two exist and what happens if you pick one.
3. Set File Compression, Video Resolution, or Trim: Quality Preset starts on Very High (Recommended), with Specific file size, Constant Bitrate, Constant Quality, and Constraint Quality alongside it. Video resolution starts on Keep original and offers presets down to 144p, a percentage, or an exact Width x Height. Trim → Time Range cuts a segment in the same pass. Audio Codec starts on AAC, with MP3 and ADPCM_SWF as alternatives.
4. Convert and Download: Click "Convert" and save the .flv. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically after a few hours — no sign-up, no watermark.

Walk-through: Choosing the Video Codec

Four entries sit in that dropdown and they are not four flavours of the same thing. Two are video codecs; two are screencast codecs that happen to live in the same container and will wreck a camera-footage job.

The practical guidance is short. If anything downstream can decode H.264, choose it — your M2TS is already H.264, so staying on that codec family means the single unavoidable re-encode does not also drop you a generation. If the target really is a pre-2008 Flash Player, leave it on FLV and accept that Sorenson Spark's H.263 lineage will look softer and cost more bits than the source did.

The two Flash Screen Video entries deserve a specific warning. Our pipeline treats them as lossless codecs and skips rate control entirely, which is why the Constant Quality mode vanishes from File Compression the moment you select one. Point a lossless screencast codec at an hour of 1080i camcorder video and you get an enormous file and a long encode for no benefit at all.

One more thing you will notice: with the default FLV codec selected, Variable Bitrate is not among the File Compression modes — Sorenson Spark does not get that mode here. Constant Bitrate, Specific file size, Constant Quality, and Constraint Quality all remain available. And on the MPEG-4-era encoders, including FLV, the box labelled CRF is not an x264-style CRF: we hand it to the encoder as a quantizer scale from 1 to 31, where 1 is best quality and biggest file.

Common Errors and How to Fix Them

• "The FLV looks soft or blocky next to my M2TS" — You are on Sorenson Spark, an H.263-derived codec a full generation behind the H.264 you started from. Set Video Codec to H.264 if your target accepts it, and keep Quality Preset on Very High.
• "The output is gigantic and the conversion crawls" — You selected Flash Video or Flash Video (v2). Those are lossless screencast codecs that ignore rate control. Switch back to FLV or H.264.
• "Constant Quality disappeared from File Compression" — Same cause as above. It is hidden for the Flash Screen Video codecs because they have no quality dial to expose.
• "No browser will play the file" — Expected, and permanent. Adobe stopped supporting Flash Player on 31 December 2020 and began blocking Flash content on 12 January 2021. Confirm your conversion worked by opening the file in VLC or mpv, which decode FLV without any Flash runtime.
• "My 5.1 surround track came out stereo" — FLV carries a single audio track and supports none of the AC-3 or linear PCM layouts an AVCHD camcorder records, so the mix is re-encoded and folded down. If surround has to survive, FLV is the wrong target.
• "My editor refuses to import the FLV" — Most current NLEs dropped FLV import alongside Flash. Convert to a live container with M2TS to MP4 instead.
• "The picture is horizontally squashed" — Your clip is one of AVCHD's 1440×1080 anamorphic modes. No pixel-aspect correction happens here, so set Width x Height to 1920 × 1080 explicitly.

When This Doesn't Work

The honest summary is that FLV is the wrong destination for almost everyone who lands here. Flash Player is gone, no browser or phone plays .flv natively, and you are starting from a format that already holds efficient HD-class H.264 — so the conversion trades that efficiency away and, on the default codec, drops a codec generation as well. There is no quality to be gained and no modern device that benefits. Convert to FLV only when a specific surviving Flash-based system will not accept anything else, and pick H.264 inside it whenever that system is new enough to cope. For durable playback everywhere, use M2TS to MP4; to travel the other way, see FLV to M2TS.

What Changes When M2TS Becomes FLV

Frequently Asked Questions

Which codec ends up inside the FLV by default?

Sorenson Spark, shown in the dropdown simply as FLV. It is a proprietary variant of H.263 and was the required video compression format for Flash Player 6 and 7, which makes it the safest pick for genuinely old players — and the least efficient, so expect a softer picture and a larger file than the H.264 source you started with. Flash Player 9 Update 3, released 3 December 2007, added H.264-in-FLV playback, so if your downstream tool is newer than that, switching Video Codec to H.264 is strictly better. On2 VP6, which Flash Player 8 introduced, is not offered on this page.

Why is there no Variable Bitrate option under File Compression?

Because you are on the default FLV codec, and Variable Bitrate is not exposed for it. What you do get is Quality Preset (starting on Very High (Recommended)), Specific file size, Constant Bitrate, Constant Quality, and Constraint Quality — enough to hit either a quality target or a size target. If you want the full rate-control set, switching Video Codec to H.264 changes which modes render, since option visibility on this page follows the codec you pick.

What are "Flash Video" and "Flash Video (v2)" in the codec list?

They are the Flash Screen Video codecs — bitmap-tile encoders compressed with zlib and designed for screencasts, not camera footage. They are lossless, which sounds appealing and is a trap here: our pipeline skips rate control entirely for them, so a long 1080i camcorder clip becomes an enormous file, and the Constant Quality mode disappears because there is no quality parameter to offer. They are in the list for completeness. For video from a camcorder or a disc, use FLV or H.264.

Is FLV still playable now that Flash Player is gone?

The web delivery model is dead; 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 current site serves it. The container itself still opens in VLC, mpv, and ffmpeg, because those decoders never depended on the Flash plug-in — which is also the reason an existing FLV can still be converted at all. This is the key difference from .swf, which was an executable application with no standalone runtime left to run it.

Will converting M2TS to FLV improve the video quality?

No, and it cannot. Both formats are lossy, the conversion is always a full re-encode rather than a stream copy, and nothing your camcorder already discarded can be recovered. With the default Sorenson Spark codec you additionally move from H.264 to an H.263-derived encoder, so coding efficiency drops and the same visual quality costs more bits. The most you can do is avoid making it worse: leave Quality Preset on Very High, keep Video resolution on Keep original, and choose H.264 if the downstream system will take it.

What happens to the AC-3 or linear PCM audio from my camcorder?

It is re-encoded. AVCHD records Dolby Digital (AC-3) in one to 5.1 channels, or uncompressed linear PCM, and FLV supports neither — its audio side covers MP3, AAC, and ADPCM, among others. Audio Codec here starts on AAC and also offers MP3 and ADPCM_SWF, all of which Flash-era players expect. The primary track survives, but a 5.1 mix folds toward stereo, because FLV is built around a single audio track per file.

Why does my FLV still show comb lines on anything that moves?

Because the source is interlaced and nothing in this converter changes that. AVCHD specifies 60i and 50i, and a large share of consumer camcorders recorded 1080i by default; each frame is woven from two fields captured a fraction of a second apart, so movement between them shows as comb teeth. There is no deinterlacing filter anywhere in this pipeline — no preset turns one on, and converting to MP4 or any other format first does not remove combing that is already baked into the frames. Deinterlace in a desktop editor and convert the progressive export instead.

My footage came out horizontally squashed — what went wrong?

Nothing failed; you hit AVCHD's anamorphic mode. The spec allows 1440×1080 as well as 1920×1080, and 1440-wide recordings store non-square pixels that are supposed to be stretched to 16:9 at playback. This converter applies no pixel-aspect correction, so once the frame is scaled it is treated as square-pixel and the picture compresses horizontally. Fix it by stating the geometry: choose Width x Height under Video resolution and enter 1920 × 1080. Native 1920×1080 recordings are unaffected.

My files are named .MTS, and how long do you keep my upload?

They are the same BDAV transport stream — camcorders write the 8.3-style .MTS name to the card, and the clip usually arrives as .m2ts after being copied to a computer — but this page accepts .m2ts only. Use MTS to FLV for camcorder-named files, or rename the file, since the contents are identical. Your upload travels over an encrypted connection, is processed on our servers, and is deleted automatically after a few hours — no sign-up, no watermark, never shared or made public. There is no fixed size cap; upload time is the real limit on a long HD recording.