Why a browser voice recorder saves WebM instead of MP3

If your voice recording downloads as mediatik-voice.webm, do not identify its format from the extension alone. The online voice recorder shows the actual MIME type reported by MediaRecorder, and that value is the one to check. The current download helper also uses .webm for an unrecognised browser-default MIME type. What remains certain is that renaming the file cannot turn it into MP3.

The short answer

Mediatik uses the browser's MediaRecorder API. Before recording, it checks WebM with Opus, OGG with Opus, audio in an MP4 container, and WebM without an explicit codec, in that order. It selects the first type that the browser reports as supported.

If the browser reports none of those candidates, mediatik lets the browser use its default. After recording, the app reads the recorder's actual mimeType and shows the format. For the known containers in its candidate list, mediatik uses a matching .webm, .ogg, or .mp4 extension.

That means one browser may produce .webm, while another may produce .ogg or .mp4. The current mediatik recorder does not promise one container across all devices, and it does not advertise MP3 export.

Why WebM can be an audio file

WebM is a container, not another word for video. A WebM file can carry only an audio track, commonly compressed with a codec such as Opus. A voice recording named mediatik-voice.webm therefore does not need to contain a video track.

A container organises data in a file, such as WebM, OGG, or MP4. A codec such as Opus compresses the audio stream. A filename extension helps software guess the container but does not change the data inside it.

A MIME type such as audio/webm;codecs=opus describes both the WebM container and the Opus audio codec. It is more precise than the .webm extension alone.

How the browser selects a format

MediaRecorder.isTypeSupported() on MDN asks whether the browser should be able to record a given MIME type. A true result reports expected support; it cannot guarantee success when resources are insufficient or the input device fails.

MediaRecorder.mimeType on MDN reports the MIME type selected by the app or browser for the resulting file. A mismatched container and codec combination may fail to record or may produce a file that players cannot handle correctly.

Mediatik therefore does not put an .mp3 name on a Blob whose actual contents are WebM. That label might look more convenient, but it would leave the encoded data unchanged and mislead the receiving app.

What to do when a service requires MP3

First confirm whether the destination truly requires MP3. Some upload forms can play WebM or MP4 even when their short hint does not list every accepted type. If the form explicitly rejects the recording:

1. Download the original from mediatik without renaming it.
2. Note the format shown beside the recording.
3. Convert a copy with a tool that actually decodes and re-encodes audio as MP3.
4. Play the MP3 before uploading it; check the beginning, end, and volume.
5. Keep the original until the upload or editing job is complete.

Changing .webm to .mp3 by hand is not conversion. The filename changes, but the original container and codec selected by the browser do not. Format validation may therefore still fail.

What mediatik does with the recording

Microphone access is requested through the browser's permission prompt. Audio chunks are collected in the open tab, then combined into a local Blob for preview and download when recording stops. The recording is not uploaded and there is no hidden server-side conversion step.

Local processing does not imply MP3 output. Encoding MP3 would require a separate codec and another processing stage. Mediatik V1 deliberately omits that stage: it saves the actual MediaRecorder result and displays its MIME type.

Check the file before using it

Note the displayed MIME type and play the recording from beginning to end. Compare the destination's accepted containers and codecs. If MP3 is mandatory, perform a real conversion instead of a rename, and keep the original until the upload or edit is complete.

For a recording that stays in the browser, open the mediatik voice recorder, allow microphone access, and check the browser-selected format before downloading the result.