ASF to AIFF Converter

ASF to AIF — the Codec Decides Whether You Get AIFF or AIFC

ASF is Microsoft's Advanced Systems Format, publicly released in 1998 and the container underneath .wma and .wmv. This page reads the audio track out of one and writes it as an uncompressed Apple audio file. Any video stream in the source is discarded — the output is audio only.

The thing worth understanding before you convert is that the .aif extension does not decide what kind of file you get; the Audio Codec dropdown does. AIFF and AIFF-C are two different form types inside the same IFF container, and the Audio Codec you pick determines which one is written. We measured all four options and the header bytes they produce, and the results are below.

Audio Codec Determines the Form Type

Each of these was produced from the same 10-second, mono, 48 kHz ASF and the resulting file header read back byte by byte:

Read that table as a compatibility ladder rather than a quality ladder. The pre-selected PCM 16-bit Big Endian is the only choice that produces a plain FORM … AIFF file — the classic 1988 structure that every Apple audio tool, every DAW and every ancient utility reads without hesitation. Big-endian is not an arbitrary preference: AIFF inherited it from the Motorola 68000 processors the format was designed on.

The other three write AIFF-C. That is a legal Apple format and Logic, Pro Tools and QuickTime handle it, but a sowt file is byte-swapped PCM and an alaw or ulaw file is 8-bit companded telephony audio at half the size and noticeably lower fidelity. If something downstream rejects your file, this dropdown is the first place to look.

One more measured detail worth knowing: the extension itself changes nothing. Writing the same PCM 16-bit big-endian audio to .aif, .aiff and .aifc produced three byte-identical files, all with the AIFF form type. Choose the extension your software expects; choose the codec for what goes inside.

How to Convert ASF to AIF

1. Upload Your ASF File: Drag one or more .asf files onto the page or click "+ Add Files". Several files can queue and process together.
2. Confirm the Audio Codec: Leave it on PCM 16-bit Big Endian for a standard AIFF. Choose PCM 16-bit Little Endian, PCM A-law or PCM mu-law only if you specifically need AIFF-C.
3. Set Audio Channel and Audio Sample Rate: Audio Channel offers Original, Mono or Stereo. Audio Sample Rate offers Original, 8000, 12000, 16000, 24000, 44100 or 48000 Hz. Leave both on Original to mirror the source; take 44100 Hz for a CD master, 48000 Hz to sit alongside video.
4. Trim if You Need To, Then Convert: The Trim group opens on "Unchanged"; switch it on to enter a Start time and Duration in seconds or as HH:MM:SS.sss. Click Convert. Files are uploaded over an encrypted connection, converted on our servers and deleted automatically after a few hours — no sign-up, no watermark, never shared or made public.

There is deliberately no File Compression group on this page. Every codec offered here is uncompressed or fixed-rate PCM, so there is no bitrate to choose and no quality preset that would mean anything. Size is decided purely by duration, sample rate, channel count and bit depth.

How Big the Output Will Be

Uncompressed PCM has an exact size, so you can work it out before you convert: sample rate x channels x bytes per sample. The arithmetic checks out against what we measured — a 30-second stereo 48 kHz conversion came back at 5,759,030 bytes, which is 192,000 bytes per second plus a small header.

If the output is bigger than you want, the levers in order of usefulness are Trim, then Mono, then a lower sample rate. Dropping to A-law or mu-law halves the size but costs real fidelity and produces an AIFF-C rather than an AIFF, so it is a last resort for anything musical.

Frequently Asked Questions

Will converting ASF to AIF improve the audio?

No, and it cannot. ASF almost always carries Windows Media Audio, which is a lossy codec — detail was permanently discarded when the file was made. Decoding those samples into uncompressed PCM reproduces exactly what the WMA decoder outputs, nothing more, in a file many times larger. AIFF is lossless relative to the decoded source, not relative to the original recording. Convert for compatibility and edit-readiness, not for a quality gain.

Why did I get a file that says AIFC when I asked for .aif?

Because the Audio Codec was not on PCM 16-bit Big Endian. Big-endian PCM is the only combination that writes a plain AIFF form; little-endian writes an AIFF-C with the sowt compression tag, and the A-law and mu-law options write AIFF-C with alaw and ulaw. All of them are valid .aif files and Apple software reads them, but if a piece of older or stricter software rejects the file, switch back to the pre-selected big-endian option and convert again.

Is there any difference between .aif and .aiff?

Not in the bytes. We wrote the same audio to both extensions and the files came out identical, form type and all. The three-letter spelling is a leftover of the old eight-plus-three filename limit, and some software matches on one and not the other, which is the only reason to choose between them. If a tool insists on the longer spelling, ASF to AIFF produces the same file under that name.

My ASF is a video file — will this still work?

Yes, provided it has a sound track. ASF is a container that may hold video and audio together, often as .wmv, or audio alone, often as .wma. This converter reads the audio stream and discards the video. If the file has no audio stream at all, the job does not quietly return a silent file — it fails, because there would be nothing to put in the output. We confirmed that by feeding through a video-only ASF and watching the encode refuse to start.

Which bit depth do I get, and can I have 24-bit?

Sixteen bits per sample, and no. The Audio Codec list on this page tops out at PCM 16-bit, which matches CD standard and is what Logic, Pro Tools and GarageBand assume for AIFF. Bit depth cannot be increased in a conversion anyway — a 16-bit render of a lossy WMA has no extra precision to store. If a mastering chain genuinely requires a deeper container, ASF to WAV exposes more PCM bit depths.

Should I use A-law or mu-law to save space?

Only for speech, and only when the destination expects it. Both are 8-bit companded encodings from the telephony world: they halve the file size by quantising loud parts more coarsely than quiet ones, which is unobtrusive on voice and clearly audible on music. They also force the AIFF-C form type. If size is the problem and the material is musical, a compressed format is the better answer — ASF to FLAC is lossless at roughly half the AIFF size, and ASF to MP3 is far smaller again.

Why is there no quality or bitrate setting on this page?

Because none of the four codecs offered has one. PCM stores every sample literally, so there is no encoder decision to expose — the only things that change the file size are duration, sample rate, channel count and bit depth, and all four are already controls on this page. That is also why the output size is exactly predictable, which the table above lets you calculate in advance.

Can I convert only part of a long recording?

Yes, and on an uncompressed format it is the most effective thing you can do. Switch Trim from "Unchanged" and enter a Start time and Duration; only that section is decoded and written. An hour of stereo 44.1 kHz AIFF is around 635 MB, so trimming to the two minutes you actually need takes it to roughly 21 MB. To cut the AIFF further after conversion, the Audio Cutter accepts AIFF files directly.

Will a DRM-protected WMA convert?

No. Some .wma and .asf files bought through legacy Windows Media stores carry DRM and refuse to decode outside an authorised player, so the job fails. Unprotected ASF — voice memos, recordings, ripped CDs without protection, archived voicemail — converts normally. There is no online workaround for a protected file; it has to be re-acquired without the protection.

What happens to my files afterwards?

Your ASF is uploaded over an encrypted connection, decoded and written on our servers, and both it and the AIFF output are deleted automatically after a few hours. Nothing is shared or made public and no account is required. Because uncompressed audio is bulky, the download is usually the slowest part of this job — trim first if you only need a section.