MTS to M4A Converter

Lift the Soundtrack Out of an AVCHD Camcorder Clip

MTS is what a Sony, Panasonic, Canon, or JVC handycam writes to its card, and the AVCHD specification puts Dolby Digital (AC-3) or Linear PCM audio next to the H.264 video inside an MPEG-2 transport stream. This page keeps the audio and throws the picture away: the result is an M4A — an MP4 container carrying an AAC track — that plays on iPhone, in Apple Music and iTunes libraries, in podcast apps, and in essentially any player made this century. The typical reasons are a concert or recital you filmed, an interview where only the words matter, a lecture, or wildlife and ambience you want as a sound file.

Two things are worth knowing before you start. The audio is always re-encoded — there is no stream copy here, so an AC-3 track becomes an AAC track rather than being repackaged — and the compression control the page opens on is the hands-off one rather than the one that gives you a predictable result. The section below spells out which control to use instead.

How to Convert MTS to M4A

1. Upload Your MTS File: Drag the .mts clip onto the page or select it with the file browser. Several clips can be queued and they all convert with the settings you choose.
2. Pick a Predictable Compression Mode: The page opens on Quality Preset, the hands-off mode, and nothing is selected in that dropdown. For a result you can plan around, switch File Compression to Variable Bitrate for a quality-targeted encode, or to Constant Bitrate and choose a rung from 8 kbps up to 384 kbps for a predictable rate.
3. Set Audio Channel, Audio Sample Rate, or Trim: Leave Audio Channel and Audio Sample Rate on ORIGINAL to inherit the camera's layout and rate, downmix to MONO to halve a voice recording, or set Trim to a Start time and Duration to keep only the part you want.
4. Convert and Download: Start the job and save the .m4a. Your file is uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours later — no sign-up, no watermark, never shared or made public.

Which Compression Mode Gives You a Predictable Result

The File Compression group offers five modes on this page, and they are not equally precise. Constant Bitrate and Custom Bitrate are at one end — you name a number and that is the number the encoder is asked for. Variable Bitrate sits in the middle, aiming at a quality tier and letting the rate follow the material. Quality Preset is at the other end: it is the hands-off mode, its dropdown shows "Highest" on load but holds no selection, and leaving it alone means the server applies its own default rather than the label on screen.

Specific file size is worth a footnote: the bitrate it works out is capped at the bitrate of the source audio track, on the reasoning that encoding above the source cannot recover detail the camera never stored. Ask for a file bigger than the original soundtrack and you get the source bitrate, not your number.

Choosing a Variable Bitrate Rung

Variable Bitrate exposes five rungs, listed best-first. They map onto the AAC encoder's five internal VBR modes:

Treat those labels as an ordered quality scale rather than a promise about the final rate. We measured the top rung producing roughly 150 kbps — above what its label suggests — and the difference between a mono and a stereo encode at the same rung was under half a kilobit per second, so the numbers do not scale with channel count the way the naming implies. If you need a specific rate, use Constant Bitrate or Custom Bitrate, which do exactly what they say.

Channels, Sample Rate, and Trimming

• Audio Channel offers ORIGINAL, MONO, and STEREO. Camcorders record stereo (and some record 5.1); downmixing an interview to MONO is the single cheapest size saving available and costs nothing you will hear on speech.
• Audio Sample Rate offers ORIGINAL plus 8000, 12000, 16000, 24000, 44100, and 48000 HZ. Leave it on ORIGINAL and the camera's rate is carried through; AVCHD soundtracks are normally 48 kHz, so 48000 HZ is the value to force if something downstream demands an explicit one. Dropping to 16000 HZ is only sensible for pure speech.
• Trim starts on Unchanged. Switch it on and set Start time and Duration, either in plain seconds or as HH:MM:SS.sss. Trimming here saves you from uploading, converting, and then cutting a second time — useful, because an AVCHD clip is a large upload for a small audio result.

Frequently Asked Questions

Does the M4A keep any of the video?

No. M4A is an audio-only use of the MP4 container, so the H.264 picture track is discarded and only the soundtrack survives. That is normally the point — a ten-minute 1080p AVCHD clip is well over a gigabyte, and the M4A that comes back is a few megabytes. If you wanted the picture too, convert to a video target instead: MTS to MP4 keeps both streams and plays everywhere.

Will the extraction lose audio quality?

Some, unavoidably, because the track is re-encoded rather than copied. AVCHD stores either Dolby Digital (AC-3), which is already lossy, or Linear PCM, which is not. Going AC-3 to AAC is a second lossy generation, and going LPCM to AAC is the first one. At the top Variable Bitrate rung or a Constant Bitrate of 192-256 kbps that step is inaudible on normal listening for camcorder material. It only accumulates if you keep re-exporting the same audio through more lossy encodes, so keep the original MTS if the recording matters.

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. Use Variable Bitrate instead if you would rather target a quality tier than a number.

What bitrate should I use for a concert versus an interview?

For music — a recital, a gig, a school concert — pick the 96k-112k Variable Bitrate rung, or a Constant Bitrate of 192 to 256 kbps. AAC at those rates is transparent enough for material that started life as a camcorder's on-board microphone, and there is little point going higher because the microphone, not the codec, is the limit. For speech, 32k-40k VBR or 96-128 kbps constant is plenty, and downmixing to mono at the same time roughly halves the file again.

Should I pick M4A or MP3 for camcorder audio?

M4A if the destination is Apple software or a modern phone: AAC gives more quality per kilobit than MP3 and needs no extra decoder anywhere current. MP3 if the destination is old car head units, older DAPs, or a system whose format list you cannot change. Both are lossy re-encodes of the same source, so neither is "safer" for the audio itself. MTS to MP3 is the same workflow with the other codec, and MTS to WAV is the choice if you need uncompressed audio to edit.

The recording is 5.1 surround — what happens to the extra channels?

AVCHD permits multichannel Dolby Digital, and the M4A you get is derived from the primary audio track. Setting Audio Channel to STEREO makes the downmix explicit rather than leaving it to the encoder's default handling, which is the safer choice if the recording matters. If you specifically need the discrete surround channels preserved rather than folded down, an audio-only AAC file in an M4A is the wrong destination for that job.

Can I extract only part of a long recording?

Yes, in two places. The Trim control on this page takes a Start time and a Duration, so you can lift a five-minute section out of a forty-minute clip in one pass. Alternatively cut the source video first with Video Cutter and convert the shorter clip — worth doing when the upload itself is the slow part. Note that our standalone Audio Cutter works on audio files, so it is the tool for trimming the M4A afterwards, not the MTS beforehand.

Why does this page reject my .m2ts file?

The accepted-extension list here is .mts only. AVCHD gets written with two different extensions in the wild — cameras use .mts on the card, while Windows, Blu-ray authoring tools, and several import utilities produce .m2ts holding what is usually the identical stream. Rename the file to .mts, or use the M2TS to M4A page, which accepts the other spelling.

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

There is no fixed per-file cap; what limits you in practice is upload size and connection speed, and AVCHD is a high-bitrate format — the specification allows up to 24 Mbps, so an hour of footage is several gigabytes even though the M4A coming back is small. Trimming or cutting first is the usual answer. Whatever you send travels over an encrypted connection, is processed on our servers, and is deleted automatically a few hours after the conversion finishes. Nothing is shared or made public, there is no sign-up, and no watermark is applied.