MTS to SWF Converter

MTS to SWF: Which Legacy Target Do You Actually Need?

You have AVCHD camcorder footage — an .mts file holding MPEG-4 AVC/H.264 video with Dolby Digital or linear PCM audio — and something on the other end is asking for a .swf. Before converting, it is worth being clear about what that request buys you, because Adobe stopped supporting Flash Player on December 31, 2020 and began blocking Flash content from running in Flash Player on January 12, 2021.

Short answer: if the requirement is genuinely "a file with a .swf extension that a legacy authoring tool or projector will ingest", this page does that. If the requirement is "video that plays", SWF is the wrong shape and MTS to MP4 is what you want. The comparison below is the decision, in one table.

SWF, FLV and MP4 Compared for Camcorder Footage

When SWF Is Genuinely the Right Target

• An un-migrated e-learning course — Captivate, Articulate or Lectora era — whose packaging step imports .swf assets and nothing newer.
• A museum, retail or trade-show kiosk still running a standalone Flash projector executable off local storage, where replacing the player is not on the table.
• A Ruffle-based archive. Ruffle is an open-source Flash Player emulator that runs natively on modern operating systems and browsers, and its software video decoder includes an H.263 module — which is the codec family Sorenson Spark belongs to — so Flash video inside a SWF has a real emulated playback path.
• Feeding a legacy authoring or ingest tool that pattern-matches on the extension before it looks at anything else.

When It Isn't

• Anything that has to play in a browser. No current browser ships Flash, and none is going to.
• Anything where quality matters. You are re-encoding modern H.264 into a 1990s-lineage codec, so matching the source's appearance costs a much higher bitrate — the conversion strictly loses.
• Anything with surround sound. SWF audio here is MP3, which tops out at two channels, so a 5.1 AC-3 camcorder track is folded down to stereo with no way to keep the surround mix.
• Anything where the real goal was a small shareable file. MTS to MP4 is smaller and plays everywhere; there is no scenario where SWF wins on size.

How to Convert MTS to SWF

1. Upload Your MTS File: Drag the .mts clip onto the page or click "Add Files". Several clips can queue and share one set of settings.
2. Set the Video Codec: FLV (Sorenson Spark) is the pre-selected codec and the one legacy Flash players expect. MJPEG is the only alternative — it stores every frame as an independent JPEG, which suits frame-accurate ingest but multiplies the file size.
3. Set Quality and Video Resolution: Quality Preset opens on "Very High (Recommended)". Constant Bitrate, Specific file size, Constant Quality and Constraint Quality are the alternatives — read the section below before touching the last two. Video resolution opens on "Keep original"; Flash-era targets usually want 480p or smaller.
4. Convert and Download: Click Convert and save the .swf. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically after a few hours — no sign-up, no watermark.

What the SWF Container Forces on You

The Quality Slider Here Is Labelled CRF but Behaves Like qscale

This is the one setting on the page that will quietly ruin your output, so it is worth spelling out. FLV and MJPEG are qscale-family encoders, not CRF-family ones. Pick "Constant Quality" and the numeric field is labelled CRF and ranges from 1 to 31 — but that range is a quantiser scale where lower is better, and the field opens at 23. On a 1 to 31 quantiser, 23 is deep into the coarse end.

The control is not broken and it is not decorative: the value you set is passed straight through as the encoder's quality parameter. It is simply mislabelled and badly defaulted. So if you use Constant Quality, drag the number down to roughly 2 to 5 before converting. If you would rather not think about it, leave the mode on Quality Preset — on a video source like AVCHD footage that path scales the source's own bitrate and works normally — or use Constraint Quality, which pairs the same quantiser with a Max bitrate ceiling so a bad quantiser value cannot run away with the file size.

Frequently Asked Questions

Will the SWF I create play in Chrome, Firefox, Edge or Safari?

No, and no setting on this page changes that. Adobe stopped supporting Flash Player on December 31, 2020 and started blocking Flash content from running in Flash Player on January 12, 2021; the browsers removed their plugin support around the same period. To play the file you need Ruffle, the open-source Flash Player emulator, or a standalone Flash Player projector executable kept from that era. If the file needs to open by double-clicking on a normal machine in 2026, convert to MP4 instead.

Why can't I choose H.264 for the SWF, when my MTS already contains H.264?

Because the SWF container as we write it takes Flash-era video: Sorenson Spark (listed as FLV) or Motion JPEG. There is no passthrough path that keeps the existing H.264 stream, and in fact the server always re-encodes — nothing here copies a stream across untouched. That is the core cost of this conversion: efficient modern video is decoded and re-compressed with a much older codec, so you need a higher bitrate to reach the same appearance.

What happens to my camcorder's 5.1 Dolby Digital track?

It becomes stereo MP3. AVCHD records Dolby Digital (AC-3) at 64 to 640 kbps or linear PCM, and SWF supports neither — the audio is re-encoded to MP3, which is limited to two channels, so a six-channel mix is folded down. The sample rate is fixed at 44100 Hz as well, with no control on the page, because that is one of the small set of rates the SWF container accepts. If keeping the surround mix matters, extract it separately before converting the video.

Should I pick FLV or MJPEG as the video codec?

FLV (Sorenson Spark) unless a specific tool asks for Motion JPEG. Sorenson Spark is what Flash players and Flash-era authoring tools expect, and it has inter-frame compression, so a talking-head clip compresses reasonably. MJPEG stores each frame as a standalone JPEG with no temporal compression at all, which makes files several times larger for the same footage. Its one advantage is that every frame is independently decodable, which some old ingest and editing tools rely on.

Why is my SWF bigger than the original MTS file?

Because Sorenson Spark is roughly a generation and a half behind H.264 in coding efficiency, so reaching similar quality takes substantially more bits per second. If you also chose MJPEG, you have removed inter-frame compression entirely and every frame costs a full JPEG. The fixes are to drop Video resolution to 480p or below — which is what Flash-era players were designed around anyway — and to use Constant Bitrate or Specific file size to cap the result outright.

What resolution should I target for a Flash-era player?

Small. Flash kiosks and courseware were typically authored at 640x480 or 800x600, and Sorenson Spark was tuned for frames in that range. Use Preset Resolutions or Resolution Percentage to bring 1080p footage down to roughly 480p. Pushing SWF to 720p or higher inflates the file, strains old players, and defeats the exercise — any machine comfortable decoding 720p Flash video can play an MP4 without an emulator.

The output looks blocky and smeared compared to the source. What went wrong?

Most likely you used Constant Quality and left the numeric field at its opening value of 23. On this page that field is a quantiser on a 1-to-31 scale where lower means better, so 23 produces a deliberately coarse encode. Set it to 2-5, or switch to Quality Preset, which behaves normally for a video source. The second possibility is simply insufficient bitrate for the resolution — a 1080p frame re-encoded into Sorenson Spark at a Flash-era bitrate will not look like the original no matter which mode you pick.

Can I convert just one section instead of the whole recording?

Yes. Switch Trim from "Unchanged" to a Time Range and set a Start time and Duration, in seconds or as HH:MM:SS.sss. This is worth doing for its own sake with SWF, since legacy players cope badly with long files. If the upload itself is the bottleneck — AVCHD records up to 24 Mbps, so clips get large fast — trim the source first with the video cutter and convert the short result. Note also that this page accepts the .mts spelling only; if your import software renamed the clip to .m2ts, use the video to SWF converter, which takes both.