MTS to FLV Converter

Convert MTS to FLV: What This Tutorial Covers

This page turns an AVCHD camcorder file (.mts) into a Flash Video (.flv) file, and it is honest with you upfront: in 2026 this is almost never the conversion you want. FLV is a dead-end format — Adobe ended Flash Player support on December 31, 2020, and no current browser can play an FLV — so this guide covers the rare cases where FLV output is still justified, the quality cost of re-encoding H.264 down to a Flash-era codec, and how to convert to MP4 instead when that is what you actually need.

How to Convert MTS to FLV

1. Upload Your MTS File: Drag and drop your .mts clip into the box or click "Add Files." You can queue several camcorder clips and convert them in one batch with the same settings.
2. Confirm the Video Codec: Open "Show All Options" and check Video Codec. The default for FLV is FLV (Sorenson Spark), the codec classic Flash players expect; switch to H.264 only if your target system explicitly supports H.264-in-FLV.
3. Set Quality or File Size: Use the Quality Preset dropdown (default "Very High (Recommended)"), or switch File Compression to Specific file size to hit a hard size budget. Trim exports a single Time Range instead of the whole clip.
4. Convert and Download: Click "Convert" and download your FLV. No sign-up, no watermark.

Walk-through: Choosing the Codec (and Why It Downgrades Quality)

Your MTS file holds H.264/AVC video — the same efficient codec used by AVCHD camcorders from Sony and Panasonic. The FLV container cannot keep that intact under its default codec, so re-encoding involves a real, unavoidable quality cost. The converter exposes a few practical choices for FLV output: FLV (Sorenson Spark), H.264, H.263, and MJPEG.

• For a classic Flash player or .swf-based system that must read the file, keep the default FLV (Sorenson Spark) codec (FourCC FLV1). It is a variant of H.263 and the most universally readable codec inside legacy Flash environments — but it compresses far less efficiently than the H.264 in your source, so expect softer detail at any setting.
• If your target explicitly supports H.264-in-FLV, pick H.264. Adobe added H.264 to the Flash pipeline in Flash Player 9 Update 3 (December 3, 2007), so it works in late-era Flash systems but not the oldest ones. This avoids the Sorenson Spark quality drop because it keeps an H.264 stream.
• For audio, the converter defaults to AAC; MP3 is the safer pick for older Sorenson Spark workflows, since MP3 was the original FLV audio format while AAC support arrived in Flash Player 9 (2007).

Because Sorenson Spark is inefficient, an aggressive File Size (%) target produces visible blocking. If quality matters, keep Quality Preset at "Very High" or use "Specific file size" with a generous budget.

Common Errors and How to Fix Them

• "The FLV won't play in my browser" — This is expected, not a fault. No current browser (Chrome, Firefox, Edge, Safari) plays FLV after the 2020 Flash shutdown. Use a standalone player such as VLC, or convert to MP4 instead.
• "Output is pixelated or blocky" — Sorenson Spark compresses less efficiently than the H.264 in your MTS source. Raise the Quality Preset to "Very High," or use "Specific file size" with a larger budget rather than an aggressive File Size (%).
• "Audio is missing or sounds wrong" — AVCHD audio is AC-3 or linear PCM, and some old players expect MP3 inside FLV. Switch the Audio Codec from AAC to MP3 and re-convert.
• "My player rejects the H.264 FLV" — Older Flash players predate H.264-in-FLV support (added late 2007). Re-export with the default FLV (Sorenson Spark) codec.
• "The FLV is larger than my MTS" — Re-encoding an efficient H.264 clip to Sorenson Spark can grow the file. Lower the output with a Preset Resolution, or target a Specific file size.

When This Doesn't Work — and What to Do Instead

For almost every modern purpose, converting camcorder footage to FLV is the wrong move. Adobe ended Flash Player support on December 31, 2020, began blocking Flash content on January 12, 2021, and recommends uninstalling Flash Player for security reasons. If your goal is footage that plays on phones, browsers, smart TVs, or editing software, convert MTS to MP4 instead — H.264/AAC in an MP4 is the universal target today, and it keeps your source quality far better than Sorenson Spark. For HTML5 streaming you control, convert MTS to WebM is the open-format equivalent. The only solid reasons to still produce FLV are feeding a legacy Flash-based streaming server (RTMP-era infrastructure still running on an intranet) or an old e-learning platform that ingests only .flv. Outside those niches, target MP4.

Frequently Asked Questions

Should I convert MTS to FLV at all in 2026?

Usually no. FLV depends on Adobe Flash, which Adobe discontinued on December 31, 2020, and no current browser plays FLV. Your MTS footage is H.264 and converts cleanly to MP4, which plays everywhere. Only choose FLV if a specific legacy system — a Flash-based streaming server or an old e-learning platform — requires a .flv file.

Will converting MTS to FLV lose quality?

Yes, if you use the default FLV (Sorenson Spark) codec. Your MTS file is H.264, an efficient modern codec, and Sorenson Spark is a much older H.263 variant that compresses worse, so fine detail softens. You can reduce the loss by keeping the Quality Preset at "Very High," or avoid it entirely by selecting the H.264 codec for FLV output if your player supports it.

What codec does the FLV output use?

By default, FLV (Sorenson Spark), FourCC FLV1 — the codec the format shipped with and the one classic Flash players read. You can switch the Video Codec to H.264 (supported in Flash Player 9 Update 3 and later), H.263, or MJPEG, but Sorenson Spark is the most broadly compatible choice for old Flash environments.

Why won't my FLV play after converting?

Because browsers removed Flash. Adobe ended Flash Player support on December 31, 2020, and began blocking Flash content on January 12, 2021, so Chrome, Firefox, Edge, and Safari no longer play FLV. The file is fine — it opens in standalone players like VLC. For anything you intend to share or stream publicly, convert to MP4 instead.

Can I keep the camcorder audio when converting to FLV?

Yes. AVCHD records AC-3 (Dolby Digital) or linear PCM audio, and the converter re-encodes it for FLV — defaulting to AAC, with MP3 available under the Audio Codec option. MP3 is the more compatible choice for older Sorenson Spark FLV workflows because it was the original FLV audio format; AAC arrived with Flash Player 9 in 2007.

Is the MTS to FLV converter private?

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