ASF to M2TS Converter

ASF to M2TS: What the .m2ts Extension Actually Changes

.m2ts is not just a longer spelling of .ts. When the output file is named .m2ts, the transport stream is written with BDAV framing — every 188-byte transport packet gets a 4-byte arrival-timestamp prefix, making 192-byte packets — because that is the packetisation Blu-ray and AVCHD players expect. Name the same encode .ts or .mts and you get plain 188-byte packets instead. This page converts a Windows Media .asf into that BDAV-framed stream, and is specific about the one thing it does not do: produce a disc.

How to Convert ASF to M2TS

1. Upload Your ASF File: Drag the .asf onto the page or click "+ Add Files" to browse. Several files can be queued and they all run with the same settings. This page accepts the .asf extension.
2. Confirm Video Codec and Audio Codec: Video Codec opens on H.264, with H.265, MPEG-1, MPEG-2, MPEG-4, Xvid and DivX also listed. Audio Codec opens on AAC, with AC3, EAC3, MP2, MP3 and DTS (DCA) available. Switch audio to AC3 if anything downstream is checking for Blu-ray or AVCHD legality.
3. Set File Compression, Resolution and Trim: File Compression opens on Quality Preset at "Very High (Recommended)"; Specific file size, Constant Bitrate, Variable Bitrate, Constant Quality and Constraint Quality are the alternatives, and on H.264 the Constant Quality slider is the 16–51 CRF scale opening at 23. Video resolution opens on "Keep original". Trim opens on "Unchanged".
4. Convert and Download: Click Convert and save the .m2ts. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark, never shared.

The Measured Difference Between .m2ts, .mts and .ts

We encoded the same source three ways with identical settings and only the output extension changed. FFmpeg's transport-stream muxer infers its BDAV mode from that extension, so the byte layout differs:

The BDAV prefix costs roughly 2% in file size and buys you the packetisation Blu-ray players, AVCHD import paths and set-top boxes were designed around. If the tool you are feeding does not care about that, ASF to MTS writes the plain 188-byte form and ASF to MP4 is smaller and plays everywhere.

What a Single .m2ts Is Not

A .m2ts file on its own is a stream, not a disc. Blu-ray and AVCHD both put their .m2ts clips inside a directory tree — a BDMV folder with STREAM, CLIPINF and PLAYLIST subfolders — and a player navigates the playlist and clip-info files, not the raw stream. Copying a converted .m2ts into such a folder does not add the index entries that describe it, so the clip usually will not appear in the player's menu.

The second gap is audio. The Blu-ray and AVCHD specifications allow Dolby AC-3, DTS and linear PCM; AAC, which is what this page selects by default, is not on that list. AAC inside a transport stream plays perfectly in VLC, mpv, and most editors, and it is the smaller choice — but if a strict importer or an authoring tool is doing the reading, set Audio Codec to AC3 before converting.

ASF as a Source

Because this is a second generation of lossy compression, the output cannot look better than the .asf did. It can easily look worse if you drop the Quality Preset or force a small target size. Leave Video resolution on "Keep original" for a standard-definition source: a 640 × 480 WMV scaled to a 1080p preset is a bigger file containing exactly the same detail.

Frequently Asked Questions

Why does my .m2ts file start with bytes other than 0x47?

Because it is BDAV-framed, and that is correct. A plain MPEG transport stream begins with the sync byte 0x47 at offset 0 and repeats every 188 bytes. The BDAV variant that Blu-ray and AVCHD use prefixes each packet with a 4-byte arrival timestamp, so the first sync byte lands at offset 4 and the stride becomes 192 bytes. Our test file opened 0e bf 46 22 47 … — a timestamp word, then the sync byte. Any tool reporting "not a transport stream" is reading it as plain TS; point it at a .ts or .mts file instead.

Should I choose AAC or AC3 for the audio?

AC3 if a Blu-ray authoring tool, a set-top box or a strict AVCHD importer is downstream, because Dolby AC-3 is one of the audio codecs those specifications actually allow and AAC is not. AAC otherwise: it is the default here, it is smaller at the same perceived quality, and every general-purpose player handles AAC inside a transport stream. The source audio is Windows Media Audio in either case, so it is being decoded and re-encoded regardless of which you pick.

I selected DTS (DCA) and got AC-3 instead — why?

FFmpeg's built-in DTS encoder is flagged experimental and unreliable, so our pipeline substitutes AC-3 rather than emit a file that may not decode cleanly. The substitution is silent in the interface. If you genuinely need a DTS track, encode it with dedicated Dolby/DTS tooling and mux it separately; if you just needed something a Blu-ray player accepts, AC-3 was the right answer anyway.

Can I burn the converted .m2ts to a Blu-ray disc directly?

Not by copying it. A Blu-ray disc is a BDMV folder tree in which clip files sit under STREAM and are described by matching CLIPINF and PLAYLIST entries; a player follows those index files rather than scanning for loose streams. Authoring software builds that structure for you — feed it this .m2ts as the source clip. The same is true of AVCHD folders on camcorder cards.

Will the picture look better than the original ASF?

No. ASF almost always carries Windows Media Video, which is lossy, and re-encoding it into H.264 is a second lossy generation. The conversion changes the packaging and the codec, not the amount of real detail in the frames. Start from a high Quality Preset — "Very High (Recommended)", or Constant Quality in the high teens on the 16–51 CRF scale — so the second pass adds as little damage as possible, and never choose a resolution preset larger than the source frame size.

Does converting to M2TS remove the interlacing from my old WMV?

No. There is no deinterlacing anywhere in this pipeline, so an interlaced source arrives with its combing baked into every frame — thin horizontal teeth along moving edges. Transport streams are perfectly happy to carry interlaced video, so nothing flags it as a problem. If the combing bothers you, deinterlace in a video editor before or after this conversion.

Why is my M2TS so much bigger than the ASF I started with?

Two reasons stack up. Transport streams carry more overhead than most containers — program tables are repeated throughout the file so a player can join mid-stream, plus the 4 extra bytes per packet that BDAV framing adds. And the default Quality Preset targets visual fidelity rather than a size budget, so a low-bitrate .asf from the streaming era gets re-encoded at a considerably higher rate. Use Specific file size or Constant Bitrate under File Compression to pin a ceiling.

My DRM-protected WMV won't convert — is there a setting for that?

There is not. ASF has digital-rights management built into the container, and files from old Windows Media stores and subscription services use it: the streams are encrypted and only a licence tied to the original account or machine can unlock them. No converter can decode a picture it cannot read, so the job fails or produces a black, silent result. Only an unprotected copy of the source can be converted.

How big a file can I upload, and what happens to it afterwards?

Encoding runs on our servers rather than on your own hardware, so the practical limit is how large a file you can upload and how long you are prepared to wait, not what your machine can handle. Uploads travel over an encrypted connection, are processed on our servers, and both the upload and the converted file are deleted automatically after a few hours. Nothing is shared or made public, there is no watermark, and no account is required.