MTS to FLV Converter

MTS to FLV Converter

FLV is a legacy target in the fullest sense. Adobe ended support for Flash Player on 31 December 2020 and began blocking Flash content from running on 12 January 2021, so nothing about this format is aimed at the modern web. People still convert to it for concrete reasons — feeding an old learning-management system, a self-hosted media server that was built around FLV, a digital-signage box, or an archive that has to stay format-consistent — and this page exists for those cases.

The source side is AVCHD: the .MTS clips a Sony, Panasonic or Canon camcorder writes, carrying H.264 video at up to 24 Mbps. Converting that into FLV is a full re-encode, and the single most important decision is which codec you put inside the container, because the one this page opens on is not the one most people should use.

FLV Format at a Glance

Codec Choices on This Page

MDN describes H.263 as a legacy format to avoid, and notes that variations on it were used as the basis for proprietary formats including Flash video and the Sorenson codec. That is precisely what the default here is: a 2002-era design being asked to compress 1080-line camcorder footage it was never intended for.

How to Convert MTS to FLV

1. Upload Your MTS File: Drag your .MTS clip onto the page or click "Add Files". This page accepts .mts; queue as many camcorder clips as you like and they convert with identical settings.
2. Change Video Codec to H.264: The page opens on FLV (Sorenson Spark). Unless your target player specifically needs that older codec, switch to H.264 — FLV containers hold it perfectly well and the quality difference at a given file size is large.
3. Set Audio Codec and File Compression: AAC is preselected; MP3 is the safer pick for the oldest Flash-era players. Then choose Constraint Quality and set the number, or Specific file size to hit a target.
4. Convert and Download: Click Convert and save the .flv. Files upload over an encrypted connection, convert on our servers, and are deleted automatically after a few hours — no sign-up, no watermark.

Why the Default Codec Is Not the One You Want

Sorenson Spark was built for dial-up-era streaming of small, low-motion video. Handing it a 1080i camcorder clip asks it to do something it was never designed for, and the result is either a large file or a soft, blocky one. H.264 — which is already what your AVCHD source contains — is a legal and well-supported payload for the FLV container, and choosing it changes three things at once:

• The quality scale becomes meaningful. With Sorenson Spark selected, the field labelled "CRF" is really qscale, capped to 1–31, where lower is better. Typing 23 out of x264 habit asks for near-worst quality. Switch to H.264 and the same control becomes a genuine 0–51 CRF scale where 23 is a sensible mid-point.
• Variable Bitrate becomes available. Sorenson Spark does not support VBR or two-pass encoding, so that mode does not appear while it is selected. With H.264 you get target, minimum and maximum bitrate fields.
• You stop fighting the container. The FLV container's own convention favours H.264 for anything recorded this century.

If your target really is a Flash-era player that cannot decode H.264 in FLV, keep Sorenson Spark and set the quality number low — 2 to 5 — and expect a large file. That is the trade the codec imposes.

Frequently Asked Questions

Can anything still play FLV files in 2026?

No browser can. Adobe ended Flash Player support on 31 December 2020 and started blocking Flash content on 12 January 2021, and no current browser ships an FLV decoder. Standalone players such as VLC still open FLV files, and some legacy server software and signage hardware continues to expect them. If you need something that plays for other people, convert MTS to MP4 instead.

Which video codec should I choose for FLV?

H.264, in almost every case. It is what your camcorder already recorded, it fits legally inside an FLV container, and it delivers far better quality per megabyte than the Sorenson Spark codec the page opens on. Choose Sorenson Spark only when you know the destination player predates H.264-in-FLV support.

Why does the page default to Sorenson Spark if H.264 is better?

It reflects the codec historically associated with the FLV container rather than the best available choice. Worth noting that the conversion backend's own fallback for FLV output is H.264 — so if no codec is specified at all, H.264 is what gets used. Selecting it explicitly in the dropdown gives you the better encoder and the better quality controls.

What number should I put in the quality field?

It depends on the codec you picked, which is why it is worth checking. With Sorenson Spark selected the field is qscale on a 1–31 scale where lower is better, so aim for 2–5 for good quality. With H.264 selected it is a real CRF scale of 0–51 where 23 is a reasonable default and lower is still better. The same control, two completely different scales.

Will converting to FLV fix the interlacing in my 1080i footage?

No. There is no deinterlacing step in this conversion, so the comb lines that appear on moving subjects in interlaced AVCHD footage are re-encoded straight into the output. No container or codec choice changes that. Deinterlacing has to be done in an editor or a player that offers the filter.

Is AAC or MP3 the better audio choice here?

AAC is preselected and sounds better at the same bitrate, which makes it the right pick for anything reasonably modern. MP3 is the more conservative choice if the destination is genuinely old Flash-era software, since it has been supported in FLV for longer. ADPCM is also offered but has no advantage for camcorder audio.

Why is my FLV file so large compared to the original MTS?

Usually because Sorenson Spark is still selected. It is a far less efficient codec than the H.264 in your source, so it needs many more bits to reach comparable quality. Switching Video Codec to H.264 typically fixes it. Check the Quality Preset too: on a video source it multiplies your camcorder's recorded bitrate, and its default sits above 1.0x, so anything below "Medium" is needed before the file starts shrinking.

Can I convert only a section of my camcorder clip?

Yes. The Trim control takes a start time and a duration, so only that portion is encoded. For longer recordings it is often quicker to cut the source first — the video cutter accepts .mts files directly, so you are not re-encoding footage you intend to discard.

My .m2ts file was rejected on this page — why?

This page accepts .mts. When camcorder clips are copied to a computer by software they are frequently renamed .m2ts, and even though the underlying stream is the same, the two extensions are handled by separate pages here. Rename the file to .mts, or use the M2TS version of this converter.

How are my uploaded camcorder files handled?

Your .MTS file is uploaded over an encrypted connection and converted on our servers. Uploaded files and their results are deleted automatically after a few hours, are never shared or made public, and there is no sign-up and no watermark on the output.