MTS to AAC Converter

Extract the Audio From an MTS File as AAC

An .mts file is AVCHD camcorder footage — the format Sony and Panasonic introduced in 2006 and wrote to memory cards for a decade. Inside is H.264 video plus a Dolby Digital (AC-3) soundtrack, or uncompressed LPCM on professional bodies. Converting to AAC throws the video away and re-encodes that soundtrack into a compact, universally playable audio file: an interview stripped off the picture, a concert recording, wildlife ambience, a wedding speech you want on your phone. This page walks through the conversion and, more importantly, through which of the quality controls to reach for when you care what comes out.

How to Convert MTS to AAC

1. Upload Your MTS File: Drag your .mts clips onto the page or click "Add Files". Camcorder cards often split a single recording across several numbered files — upload them individually and convert each.
2. Set the Bitrate Under "File Compression": The mode selector opens on "Quality Preset", which is the hands-off option — for a result you can predict, switch to "Variable Bitrate" and choose a rung, or to "Constant Bitrate" and pick a value such as 128 or 192 kbps. This is the setting that decides your file size and quality.
3. Check Audio Channel, Audio Sample Rate and Trim (Optional): Leave "Audio Sample Rate" on Original to keep the camcorder's 48 kHz; use "Audio Channel" to fold a stereo recording down to Mono for speech; use "Trim" with a start time and duration to take only part of the clip.
4. Convert and Download: Click Convert and download the .aac. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically after a few hours. No sign-up, no watermark.

Which Quality Control to Reach For Here

This is the one thing worth knowing before you convert, and it is not obvious from the interface. The "File Compression" group holds five rate-control modes, and they differ mainly in how precisely you can predict the result — from Constant Bitrate, where you name the number yourself, to Quality Preset, where you hand the decision to the server.

About those Variable Bitrate labels: read them as an ordered five-step quality scale rather than as a promise about the delivered bitrate. They are inherited from an upstream table of per-channel targets, and measurement through our pipeline does not match the labels — at the top rung we measured 149.6 kbps for a mono conversion and 150.1 kbps for stereo, so the rate barely moves with channel count and the top rung overshoots its "96k–112k" name. Treat the bottom rung as the smallest file and the top as the best quality, and use Constant Bitrate whenever you need to know the number in advance.

What Comes Out of an AVCHD Soundtrack

Two consequences worth planning around. First, because AC-3 is already lossy, converting to AAC is a second lossy generation; that is fine at a sensible bitrate but it is a reason not to economise down to 64 kbps on music. Second, a .aac file is a bare bitstream rather than an MP4-family container, so it does not carry cover art or chapters the way an M4A does. If you want tags and artwork and a file that drops cleanly into a music library, MTS to M4A is the better target; if you want the most universally accepted audio file in existence, MTS to MP3 is.

Common Errors and How to Fix Them

• "I picked a Quality Preset but the file is not the size I expected" — Quality Preset is the hands-off mode and the least predictable control here, and nothing is pre-selected in it, so the server may simply be applying its own default. Switch the mode to Variable Bitrate or Constant Bitrate and name what you want.
• "My camcorder recording is split into several MTS files" — AVCHD cameras split long takes across numbered files on the card. Convert each one and join the resulting audio in an editor, or join the video first and convert the joined file.
• "The speech sounds thin after conversion" — Check the Audio Channel setting. Folding to Mono sums the channels, which is usually good for a single voice but can hollow out a recording where the interesting sound is spread across the stereo field.
• "The file will not import into my music app" — Bare .aac streams are handled inconsistently by media libraries. Convert to M4A instead, which is the same AAC audio inside an MP4 container.
• "I only want a 30-second section" — Use the "Trim" control on this page with a start time and duration rather than converting the whole clip. Trimming the source video first with Video Cutter also works; a general audio cutter will not accept an MTS file directly.
• "The audio is out of sync with what I expected" — Trim start times are applied to the source timeline. If a camcorder file has an unusual timestamp start, convert the whole file first and trim the resulting audio afterwards.

When This Doesn't Work

If the MTS was recorded with LPCM audio on a professional body and you are converting specifically to preserve fidelity, AAC is the wrong destination — you are compressing something that was uncompressed. Convert to FLAC or WAV instead and keep the lossless chain intact. If the file is a partial card copy — AVCHD spreads a recording across a directory structure, and lifting a single .mts out of it usually works, but a truncated file will not — re-copy from the card. And nothing on this page deinterlaces or otherwise touches the picture: the video track is simply discarded, so if you want the footage as well as the audio, convert the clip separately to a video format rather than expecting one pass to give you both.

Frequently Asked Questions

Which control on this page actually sets the bitrate?

"Constant Bitrate" (or "Custom Bitrate", if you want a value the dropdown does not list). The "Quality Preset" dropdown displays "Highest" when the page loads, but nothing is pre-selected there — if you never touch it, the server falls back to its own default rather than the value you can see. The presets are also the least predictable control here, so when the output rate matters, name it explicitly with Constant Bitrate and check the result in your player's file-info panel. "Variable Bitrate" is the middle ground: you choose a quality rung and let the encoder settle the rate.

What bitrate should I choose for MTS audio?

For speech — interviews, lectures, family video — 96 to 128 kbps is plenty, and folding to Mono at the same bitrate makes it sound better rather than worse. For music or ambience recorded in stereo, 192 kbps is a safe transparent choice, and going above 256 kbps is hard to justify when the source is already lossy AC-3. If file size is your constraint rather than quality, Variable Bitrate's lower rungs shrink quiet material more aggressively than a fixed bitrate does.

Do the Variable Bitrate labels mean I get that bitrate?

No, and this is worth stating plainly. Those five rungs map onto the encoder's internal VBR quality scale, and the kbps ranges in the labels come from an upstream per-channel reference table rather than from what our pipeline delivers. Measuring the top rung through our own conversion gave 149.6 kbps for mono and 150.1 kbps for stereo — barely different from each other, and well above the "96k–112k" the label suggests. Use the rungs as a quality ladder from smallest to best, and switch to Constant Bitrate when the exact number matters.

Is converting AVCHD audio to AAC lossy twice?

Yes. AVCHD normally records Dolby Digital AC-3, which is already a lossy format, and encoding that to AAC is a second lossy generation. In practice this is unproblematic at 128 kbps and up, because AAC is efficient enough that the second pass costs far less than the first did. Where it does matter is at low bitrates, or when the camcorder recorded uncompressed LPCM — in that case you are throwing away real fidelity, and FLAC or WAV is a better destination than AAC.

Will the sample rate change during conversion?

Not unless you ask it to. AVCHD audio is 48 kHz, and leaving "Audio Sample Rate" on Original passes that through. The dropdown also offers 8000, 12000, 16000, 24000, 44100 and 48000 Hz if you have a reason to resample — for example matching a project that runs at 44.1 kHz. Downsampling to 8 or 16 kHz is only sensible for speech destined for something like a voice archive, and it is not reversible, so keep the 48 kHz version if the recording matters.

Can I extract just one section of a long camcorder recording?

Yes, using the "Trim" control on this page. Switch it from "Unchanged", then set a start time and a duration in either seconds or HH:MM:SS.sss form, and only that span is encoded. This is faster and cleaner than converting an hour of footage and cutting afterwards. Note that a generic audio cutter will not take an MTS file as input, so if you prefer to cut before converting, do it on the video with a video-side trimming tool.

Why is my output a single stereo track when the camcorder recorded 5.1?

Because most conversions here resolve to a stereo layout unless you specify otherwise, and AAC in a bare .aac stream is rarely used for surround in practice. If preserving a multichannel mix matters, keeping the audio in its original AC-3 form or converting to a container format that carries surround cleanly is a better route than a bare AAC stream. For everything else — voice, music, ambience — stereo or mono is what you want, and the "Audio Channel" dropdown chooses between them.

How are my files handled while they convert?

Your MTS is uploaded to our servers over an encrypted connection, the audio track is decoded and re-encoded to AAC there, and both the upload and the result are deleted automatically after a few hours. There is no sign-up and no watermark, and your recordings are never shared or made public. The practical limit is upload size and time: AVCHD records at up to 24 Mbit/s, so an hour of footage is several gigabytes even though the audio you want out of it is a few tens of megabytes. Trimming to the section you need before uploading, where possible, saves the most time.