Free Audio Converter

Worked example

Drop a 3-minute stereo WAV of 30.3 MB (44.1 kHz, 16-bit). The strip under the file shows "Source" WAV, "Duration" 3:00 and "Size" 30.3 MB, and "Convert to" has MP3 selected, because only an .mp3 source defaults to M4A. "Bitrate" is on "Match source", which for a lossless file means 192 kbps, so "Estimated output:" reads ~4.1 MB (192 kbps times 180 seconds). Press "Convert to MP3". The page shows "Converted to MP3" with the size and a "Download" button, and the file keeps its name with .mp3 as the extension. Now press "Voice preset": the hint changes to "Voice preset is on: mono, 16 kHz, 64 kbps.", "Advanced options" opens and the estimate drops to ~1.4 MB.

Which settings to use, and the limits

• Pick the format for where the file will play. "Convert to" offers MP3, M4A (AAC), AAC, OGG (Vorbis), Opus, FLAC, ALAC (Apple Lossless), WAV and AIFF, and a ✦ marks the lossless ones. The page describes MP3 as "Plays on everything", ALAC as "Apple Lossless, for iPhone and Mac" and Opus as "Best quality per MB". An .mp3 source defaults to M4A; anything else defaults to MP3. Besides audio, the tool accepts video files (.mp4, .mov, .mkv, .webm, .3gp, .m4v) and takes out the sound track, plus .wma, .amr, .aiff and .opus audio. ALAC is written into an .m4a file.
• Set the bitrate, or leave it on Match source. "Bitrate" shows for the lossy formats only (MP3, M4A, AAC, OGG, Opus): "Match source", then 64, 96, 128, 192, 256 and 320 kbps, with 320 starred. For a lossy source, Match source uses its own bitrate rounded to the nearest option, shown for example as "Match source (128 kbps)"; for a lossless source it uses 192 kbps. The page says 192 kbps is transparent for most listening and that a higher bitrate means a larger file. When the target format equals the source format, an amber notice warns that converting only re-encodes the file.
• Use the Voice preset for voice notes and transcription. The "Voice preset" button sets mono, 16 kHz and 64 kbps in one press and opens "Advanced options", where "Channels" (Keep original, Mono, Stereo) and "Sample rate" (16, 22.05, 32, 44.1 and 48 kHz) can also be set by hand. The page describes the preset as small files for voice notes and speech-to-text tools. Opus is a special case: a mono Opus file uses your sample rate rounded up to one Opus allows (8, 12, 16, 24 or 48 kHz), but a stereo Opus file is always written at 48 kHz and ignores the Sample rate box.
• Choose the bit depth for WAV and AIFF. For these two formats a "Bit depth" row offers "Match source", "16-bit" and "24-bit". Match source writes 24-bit only when the source is deeper than 16-bit, and 16-bit otherwise. WAV and AIFF are uncompressed, about 10 MB per minute at 16-bit, and FLAC or ALAC come out at roughly 60 percent of that. Converting a lossy file such as MP3 to a lossless format makes it larger without restoring detail, and the page warns about this. Going from a lossless source to a lossy format discards detail for good, so keep the original.
• Keep tags and cover art, or even out the volume. The "Keep tags and cover art" box appears when the target is MP3, M4A, ALAC or FLAC and the source has an embedded picture (in a batch it always shows). It is ticked by default and copies title, artist and the album picture; if the picture makes the conversion fail, the tool retries without it so you still get the audio. "Normalize loudness" runs a loudness filter aimed at −16 LUFS (EBU R128), handy for voice memos and podcasts. If you have not chosen a sample rate, the output then keeps the source's rate.
• Convert several files in one go. Drop two or more files, or press "+ Add more files" after the first. They join a queue and run one at a time with the settings on screen, which are read as each file starts, so the panel is locked while the queue runs. The start button reads like "Convert 3 files to MP3". Finished rows say "Done" with a size, and "Download all (3)" saves a ZIP named converted-audio. A failed row shows the reason, "Retry failed (1)" runs it again and "Stop" ends the run. Each file is size-checked on its own; an oversized one is refused and the rest are queued.

Common problems and how to fix them

It says "This file is 2.6 GB, which is too large to process in your browser on this device (limit ~2 GB). Try a smaller file or trim a shorter clip first."

The limit is checked when you add the file: about 2 GB on a normal computer, 1 GB on one reporting 4 GB of memory or less, and 400 MB on a phone or tablet. Above 800 MB, 400 MB or 150 MB respectively you get a caution instead: "This file is 900 MB. Large files can be slow and may run out of memory in the browser. If it fails, try a shorter clip." An out-of-memory message later means the file is too big for this device.

It says "This file has no audio track to convert."

After opening the file, the tool reads its streams. If it finds no audio but does find a video stream or a duration, it stops with this message. A screen recording made without sound is a typical case. Pick a file that has sound. In a batch the same sentence appears on the row of that file, and the other files carry on.

It says "This file couldn't be read — it may be incomplete (still downloading or only partly copied) or not a real video/audio file. Try the original file again."

The media engine reported a missing header or invalid data, such as "moov atom not found", "Invalid data found when processing input" or a failed EBML header. That points to a file cut short by an interrupted download or copy, or a file that is not really audio or video. Download or copy the original again, wait until it finishes, and add the new copy.

The player is missing and the page says "Your browser can't preview this format, but it can still be converted."

This is a notice, not an error. The browser's own player could not load the file, which happens with formats such as WMA, AMR, AIFF and some Opus files. The conversion uses the media engine instead, which also reads the length, bitrate and cover art, so the estimate and "Match source" still work. Press "Convert to MP3" as usual.

It says "This file changed or moved after you picked it — please choose it again."

The file was moved, renamed, deleted or edited after you added it, so the browser can no longer read it. Cloud-synced folders such as OneDrive or iCloud cause this when a file is only a placeholder. A 0-byte placeholder is refused when you add it, with a message to download it to the device first. Choose the file again from its current place.

How it compares

The Audio Converter re-encodes with FFmpeg in your browser. It writes nine formats, reads audio and the sound track of video files, and runs a queue of many files into one ZIP. It is a converter, not an editor: it does not trim, join, fade or edit tags (title, artist and picture are copied, not edited). The settings are bitrate, channels, sample rate, bit depth and loudness, with no encoder-specific options, and stereo Opus is made by FFmpeg's built-in Opus encoder. Very large files are limited by browser memory, about 2 GB, 1 GB or 400 MB depending on the device, and a desktop converter is the better choice near those sizes. In exchange nothing needs installing, and the page says nothing is uploaded.