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 is written for one specific reader: someone whose old Flash-based courseware, CMS, or web player still ingests .flv and accepts nothing else. Read the honesty note in the first step before you start — for almost every other goal, M2TS to MP4 is the right tool, not this one.

How to Convert M2TS to FLV

1. Upload Your M2TS File: Drag and drop your .m2ts (or .mts) clip from the camcorder's BDMV/STREAM folder onto the page, or click "+ Add Files" to browse. Batch upload is supported, so several clips can be queued and converted with the same settings.
2. Pick Video Codec and Quality Preset: Under Advanced Options, Video Codec defaults to FLV (Sorenson Spark) for the broadest legacy-player compatibility; switch it to H.264 if your target tool accepts H.264-in-FLV for noticeably sharper output at the same size. Leave Quality Preset on "Very High (Recommended)", or open File Compression for Constant Bitrate, Constant Quality, or a Specific file size.
3. Set Resolution and Trim (Optional): Under Video resolution choose Keep original, a Preset Resolution, Resolution Percentage, or a custom Width x Height. Use Trim → Time Range to cut a single segment out of a long take in the same pass.
4. Convert and Download: Click "Convert" and save your .flv file. No sign-up, no watermark.

Walk-through: Choosing the FLV Codec (the step that actually matters)

The Video Codec dropdown is where this conversion succeeds or fails, because the right answer depends entirely on what is reading the file on the other end. M2TS already stores efficient H.264/AVC, so re-encoding into a Flash-era container is a step backwards no matter what — the question is only how far back you go.

• If your target is an old Flash Player or a pre-2008 player widget: leave Video Codec on FLV (Sorenson Spark). This is the original H.263-based codec every Flash Player from version 6 onward could decode — the safest choice for genuinely old systems, but the least efficient, so expect a softer picture and a larger file than the source.
• If your target tool is newer but still demands the .flv extension: switch Video Codec to H.264. Flash Player 9 Update 3 (December 3, 2007) added H.264-in-FLV playback, so any player from that era forward can read it, and you keep the efficient codec your M2TS already used — only the container is dead, not the picture.
• For the audio: Audio Codec defaults to AAC, with MP3 also selectable. M2TS carries Dolby Digital (AC-3) or LPCM, neither of which FLV supports, so the soundtrack is always re-encoded to AAC or MP3 — both of which Flash-era players expect.

Common Errors and How to Fix Them

• "The FLV looks softer / blockier than my M2TS" — You converted with FLV (Sorenson Spark), an old H.263-based codec that is far less efficient than the H.264 your M2TS already used. Set Video Codec to H.264 and keep Quality Preset on "Very High" if your target accepts H.264-in-FLV.
• "My browser won't play the FLV" — Expected. No modern browser plays .flv natively — Adobe ended Flash Player support on December 31, 2020 and blocked Flash content from January 12, 2021. Open the file in VLC or MPV to confirm it converted correctly; the container still plays there.
• "The output file is bigger than the source" — Sorenson Spark needs more bits than H.264 to hold the same picture. Either switch to H.264-in-FLV, or use File Compression → Specific file size to cap the output.
• "The 5.1 surround track collapsed to stereo" — FLV is built around a single AAC or MP3 audio track and does not carry AC-3/LPCM, so a multichannel mix is folded down. If keeping surround matters more than the .flv extension, this is the wrong target.
• "iMovie or my editor won't import the FLV" — Most modern editors dropped FLV import along with Flash. Convert to a current container with M2TS to MP4 instead.

When This Doesn't Work

The honest answer is that FLV is the wrong target for almost everyone. Flash Player is gone, no browser or phone plays .flv, and you start from M2TS — which already holds efficient HD-class H.264 — so converting to FLV trades that efficiency for a dead container and, if you pick Sorenson Spark, an old codec on top of it. There is no quality to be gained and no modern device that benefits. Convert to FLV only when a specific un-migrated Flash-based system — legacy courseware, an old learning-management system, or a vintage CMS player — refuses to accept anything else. For durable, universal playback that keeps the H.264 stream, use M2TS to MP4. To go the other direction, see FLV to M2TS.

Frequently Asked Questions

Will converting M2TS to FLV improve the video quality?

No — and that is a hard limit, not a tool flaw. M2TS already stores efficient H.264/AVC, often at 1080p, and FLV re-encodes it to Sorenson Spark or H.264 inside the Flash container. Because the source is lossy and the output is lossy, no detail the M2TS already discarded can be regained. Worse, the default FLV codec (Sorenson Spark) is an older, less efficient generation than H.264, so you can actually lose coding efficiency and end up with a softer, larger file. Leave Quality Preset on "Very High" so the re-encode itself isn't the bottleneck, and choose H.264-in-FLV if your target allows it.

Should I really convert to FLV, or is MP4 the better target?

For almost everyone, MP4. FLV made sense when Flash Player was installed on virtually every desktop; that era ended in 2021. Your M2TS already holds efficient H.264, so M2TS to MP4 keeps that exact stream, plays in every modern browser and on phones, and stays small. In our testing, a 1080p AVCHD M2TS clip converted to FLV with the default Sorenson Spark codec produced a softer, larger file that only VLC or a dedicated player would open, while the MP4 version played everywhere unchanged. Choose FLV only when a legacy Flash-based player or courseware tool will not accept anything else.

Which codec does this put inside the FLV — Sorenson Spark or H.264?

By default, FLV (Sorenson Spark), the original H.263-based codec that every Flash Player from version 6 onward could decode — the safest choice for genuinely old players. If your downstream tool is newer (Flash Player 9 Update 3, released December 3, 2007, added H.264-in-FLV support), switch Video Codec to H.264 under Advanced Options to keep the efficient codec your M2TS already used. We do not target On2 VP6 here; Sorenson Spark and H.264 cover the realistic compatibility range.

Is FLV still playable now that Flash Player is gone?

The Flash web-delivery workflow is dead, but the file is not unreadable. Adobe ended Flash Player support on December 31, 2020 and began blocking Flash content on January 12, 2021, so no browser plays .flv natively and no modern site serves it. The container itself still opens in VLC, ffmpeg, and MPV-class players, because those decoders never depended on the Flash plug-in — which is also why an FLV can be re-converted at all. This is the key difference from .swf, which was an executable application with no standalone runtime left.

What happens to the AC-3 or LPCM audio in my M2TS file?

It is re-encoded. AVCHD camcorders and Blu-ray streams record Dolby Digital (AC-3) or linear PCM, and FLV supports neither, so the soundtrack is converted to AAC by default, with MP3 also available under Audio Codec — both of which Flash-era players expect. The primary track is preserved, but a 5.1 mix is folded toward stereo, since FLV is built around a single audio track per file. If your file is named .mts rather than .m2ts, the dedicated MTS to FLV converter handles it identically.

How are my files handled, and how long are they kept?

Your file is uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after the conversion — no sign-up, no watermark, never shared or made public.