What happens after you choose a file
PrivateMP3 first identifies the container, lists its audio tracks and reads the duration. It selects the first audio track and shows an Audio track picker only when more than one is found. The selected track is then decoded progressively to build the waveform. A re-encoded output waits for the Ready message; an eligible unchanged AAC-to-M4A copy is the exception because it does not need decoded samples.
The Play button is a separate browser preview of the original local file. A disabled Play button does not by itself mean conversion will fail. The waveform and Convert status are the relevant checks for the selected audio track.
Use the editor in this order
- Open a file already stored on your device.
- If an Audio track picker appears, choose the intended language or mix before editing.
- Wait for Ready, then drag over a section you want to inspect.
- Press Remove selection to delete that interval, or Keep only selection to discard everything outside it. Dragging a selection alone does not change the output.
- Repeat Remove selection for additional unwanted intervals. The kept sections remain in their source order.
- Choose an output, press Convert and use Save file only after the result is finished.
Changing the audio track after editing opens a warning because the selection, cuts, volume regions and undo history belong to the old timeline. Continuing clears them and starts a new waveform scan.
MP3, M4A and WAV are different processing choices
| Output | What this implementation writes |
|---|---|
| MP3 | A new 192 kbps MP3 from the selected decodable track. |
| Unedited AAC → M4A | The original AAC packets in a newly written M4A container. |
| Edited or non-AAC → M4A | New 192 kbps AAC after decoding. |
| WAV | Decoded audio as 16-bit PCM. |
There is no bitrate picker. MP3 and newly encoded M4A use the fixed 192 kbps target. M4A avoids re-encoding only when the visible copy note appears; a cut or volume change disables that route. WAV avoids another lossy encode, but it cannot improve a source that was already compressed.
Supported container does not guarantee a usable codec
The file picker accepts MP4, MOV, MKV, WebM, MPEG-TS, MP3, M4A, AAC, WAV, OGG and FLAC inputs. A container can still hold an audio codec that the current browser cannot decode. Multiple tracks in one file can also have different codecs, so one may work while another displays no decoder.
AVI, WMV, WMA, FLV and AIFF are not accepted by the shipped container reader. Renaming an unsupported file does not change its internal format. If the container opens but the waveform does not, use the stage-by-stage diagnostic guide rather than guessing from the extension.
Local processing removes the upload, not device limits
The browser reads the selected file from local storage and the conversion worker processes it on the same device. Page assets, advertising, Google Analytics and Cloudflare performance measurement still make their own network requests, but those requests do not carry the selected media. The local-processing guide shows how to inspect this distinction.
The page imposes neither a subscription tier nor a configured byte limit. Large files still take longer to scan and convert, need sufficient browser storage for the output, and can be interrupted when a phone suspends a background tab. No untested gigabyte, duration or processing-time guarantee is used here.
Process only media you own or otherwise have the right to use. The page reads local files; it has no URL input, external download function or access-control bypass.