MTS to AC3 Converter

Extract AC3 Audio from MTS: What This Tutorial Covers

This tool pulls the soundtrack out of an MTS (AVCHD camcorder) clip and writes it as a standalone AC3 (Dolby Digital) file. There is a nice detail here most converters gloss over: AVCHD's own audio codec is usually Dolby AC-3 already, so for most camcorder footage .ac3 is the recording's native audio format rather than a foreign one. This walk-through covers what actually lives inside an MTS file, when extracting to .ac3 is the right call (the big one is DVD authoring — pairing this audio with a demuxed video stream), why this tool re-encodes rather than copies the stream untouched, and which target to pick instead when you just want sound you can play on a phone.

How to Convert MTS to AC3

1. Upload Your MTS File: Drag and drop your .mts (or .m2ts) file onto the page, or click "+ Add Files" to browse for it. Queue several clips to extract them in one batch with the same settings.
2. Set the Quality Preset or Bitrate: Open "Show All Options" and choose a Quality Preset under File Compression, or switch to Custom Bitrate / Constant Bitrate to set an exact rate. AC3 tops out at 640 kbit/s; for DVD-Video stay at or below 448 kbit/s to remain spec-compliant.
3. Set the Audio Channel, Sample Rate, or Trim (Optional): Leave Audio Channel on "Original" to keep the source layout, or force Mono / Stereo; the Audio Codec is already AC3 for .ac3 output. Adjust Audio Sample Rate, or use Trim to export only part of a long recording.
4. Convert and Download: Click "Convert" and download your .ac3 file individually or as a ZIP. No sign-up, no watermark.

Walk-through: AVCHD's Native Audio, and Why This Re-encodes

MTS is the file an AVCHD camcorder writes — H.264 video and an audio track inside an MPEG-2 transport stream. AVCHD was introduced in 2006 by Sony and Panasonic, and its audio is one of two codecs: Dolby AC-3 (Dolby Digital), carrying 1 to 5.1 channels at 64–640 kbit/s, or uncompressed linear PCM on professional models. Because consumer camcorders overwhelmingly record AC-3, extracting your MTS audio to .ac3 usually keeps the same codec family the camcorder used in the first place.

That raises a fair question: if the audio is already AC-3, does this just copy the stream out untouched? No — this tool re-encodes. The honest tell is the controls themselves: you can set a bitrate, change the channel layout, and pick a sample rate, and a true stream copy could not do any of that. So treat the output as a fresh AC3 encode, and set the bitrate sensibly:

• Source is already AC-3 (most camcorder MTS): keep the AC3 output rate at or above the source rate — typically 256–448 kbps for a stereo or 5.1 track — so the re-encode adds as little second-generation loss as possible.
• Source is LPCM (some professional rigs): the uncompressed audio is encoded to AC3 here, which is the first lossy step; 448 kbps is a safe, DVD-legal choice for a 5.1 or stereo master.
• Targeting a DVD: stay at or below 448 kbit/s, the DVD-Video / ATSC ceiling for AC3, regardless of source.

AC3 itself is Dolby Digital — a lossy perceptual codec (Modified Discrete Cosine Transform) that became the audio standard for DVD-Video, ATSC digital TV, and home-theater receivers. It dates to February 1991, with its first major cinema outing on Batman Returns in 1992, and carries up to 5.1 channels at up to 640 kbit/s.

The DVD-Authoring Workflow

DVD-authoring tools such as DVDStyler or TMPGEnc Authoring Works build a disc from demuxed assets — a separate video stream and a separate audio stream, imported side by side and multiplexed into the final title. This page produces the audio half: the .ac3 Dolby Digital track. For the video half, convert the same MTS file with MTS to M2V, which re-encodes the H.264 picture to the MPEG-2 elementary stream DVDs require. Feed both the .m2v and the .ac3 into your authoring tool and it will assemble a compliant disc. Staying at or below 448 kbit/s on the AC3 keeps the audio within DVD spec.

Common Errors and How to Fix Them

• "My 5.1 camcorder track came out as stereo." Check the Audio Channel option — if it was forced to Stereo, the surround channels were folded down. Leave it on "Original" to preserve whatever channel layout the MTS actually contains. Surround only exists in the output if the source already had discrete 5.1 channels; the tool cannot invent them.
• "The .ac3 won't open in QuickTime or Apple Music on my Mac." Some macOS releases (notably High Sierra) ship without an AC-3 decoder, so a bare .ac3 may refuse to play even though the file is fine. For Mac playback or editing, extract to MTS to WAV or MTS to MP3 instead.
• "The audio sounds no better than I hoped." AC3 is lossy, and if your source was already AC-3 this is a lossy-to-lossy re-encode. Keep the output bitrate at or above the source rate to minimize added loss — pushing it past the source does not recover detail, it only avoids stacking new artifacts.
• "My DVD tool rejected the AC3." Most often the bitrate exceeded the DVD ceiling. Re-export at 448 kbit/s or lower, which is the AC3 cap DVD-Video and ATSC enforce.
• "The file is huge / won't upload." A long AVCHD clip can be a sizeable upload even though only the audio is extracted. Use Trim to grab just the part you need, or convert a few files at a time so each upload finishes over your connection.

When This Doesn't Work

If your MTS file is partially corrupted — common after an interrupted card copy or a transfer that was cut off — the audio stream can be unreadable even when a player scrubs part of the video. And .ac3 is a delivery format aimed at discs and receivers, not a convenient editing or playback target: most phones, browsers, and Apple's Music app do not decode a standalone AC3 file. If you only need the AVCHD soundtrack to play or share, MTS to MP3 is the portable choice; to edit it, MTS to WAV gives you an uncompressed master with no further lossy loss; and if you actually want to keep the video, MTS to MP4 re-wraps picture and sound into one modern file. Reach for .ac3 specifically when a DVD-authoring tool or home-theater chain asks for a Dolby Digital track.

Frequently Asked Questions

Is the AC3 just copied out of my MTS, or re-encoded?

Re-encoded. AVCHD camcorders usually record Dolby AC-3 already, so .ac3 keeps the same codec family — but this tool does not pass the stream through untouched. The bitrate, channel, and sample-rate controls only make sense for an encode, so treat the output as a fresh AC3 file. If your source was AC-3, set the output bitrate at or above the source rate (256–448 kbps is typical) to keep the second-generation loss minimal; if your source was LPCM, the audio is encoded to AC3 in this step.

I have a .m2v and need the matching audio for a DVD — is this the right tool?

Yes. DVD-authoring tools work from demuxed assets: a separate MPEG-2 video stream and a separate audio file. The MTS to M2V page produces the video half, and this page produces the audio half — the .ac3 Dolby Digital track DVD-Video uses. Convert the same MTS file both ways, import the .m2v and the .ac3 into DVDStyler or TMPGEnc Authoring Works, and it will multiplex them into a compliant title. Keep the AC3 at 448 kbit/s or lower to stay within the DVD spec.

Will I get 5.1 surround in the AC3 output?

Only if your MTS source already has it. AVCHD's AC-3 audio can carry up to 5.1 channels, and leaving Audio Channel on "Original" preserves whatever the camcorder recorded — many consumer clips are stereo, while some rigs capture 5.1. The converter will not upmix a stereo track into surround; it can keep or fold down channels, not invent them. If "Original" gives you stereo, that is what was in the file.

What bitrate should I choose for the AC3?

AC3 ranges up to 640 kbit/s, but for anything DVD-related stay at or below 448 kbit/s, the ceiling DVD-Video and ATSC broadcast enforce. If your source MTS is already AC-3, match or slightly exceed its rate rather than going to the maximum — a higher number than the source does not recover quality, it just makes a larger file. For a stereo soundtrack, 256–448 kbps covers almost every case.

Why does an MTS already have AC-3 audio inside it?

Because that is part of the AVCHD specification. When Sony and Panasonic defined AVCHD in 2006, they chose Dolby AC-3 (Dolby Digital) as the standard audio codec for consumer camcorders (with linear PCM as an alternative on professional models). So the sound in a typical .mts clip is Dolby Digital from the moment it is recorded — extracting it to .ac3 is pulling out audio that was already in that format. In our testing, a one-minute 1080p MTS clip yielded an AC3 file of roughly 3 MB at a 448 kbps stereo rate, since audio size depends on bitrate and duration, not on the video resolution.

I just want to play the camcorder audio — should I pick AC3 or something else?

Something else, in most cases. A standalone .ac3 is built for DVD players and AV receivers, not phones, browsers, or Apple Music — and some macOS versions cannot even decode it. For everyday playback, MTS to MP3 plays virtually everywhere; to edit the audio, MTS to WAV gives an uncompressed master without adding another lossy generation. Choose .ac3 only when a disc-authoring tool or home-theater device specifically needs a Dolby Digital track.

How are my files handled, and is there a size limit?

Your MTS 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. The main practical limit is upload size and time rather than the extraction itself, so a long AVCHD clip can take a while to upload even though pulling out the audio is quick; trim it or convert a few files at a time if needed.