Broadcast WAV to MP3 / AAC for transcription with timecode & metadata preserved.
Forgot to roll MP3s for transcription? Producer asking for MP3s after the interview is already over? Happens to the best of us. I got you, bruvs.
.WAV.MP3.AAC
Drop in WAVs. Get transcription ready MP3s or AACs back.
Timecode and scene/take info carried across. A 30 minute interview at 48 kHz / 24-bit goes from a 494 MB WAV to a 28 MB MP3, about 18x smaller, at the default 128 kbps.
Your master WAV is never touched. It is opened read only and every output is a brand new file, so the original stays the master for conform and sync.
Use it right here in the page, or install it as a real app on your phone, laptop or desktop with the button below and run the whole thing offline, on set, with no internet at all.
And even when you use it right here in the browser: every conversion happens on your own machine. Nothing is uploaded, so you never sit around waiting on your WAVs to crawl up to somebody's server, and confidential dailies never leave the room.
● 100% on this device. Audio is never uploaded
Works in all modern desktop browsers: Chrome, Edge, Firefox, Safari. MP3 output everywhere; .aac output needs Chrome or Edge. For big cards and long files, use a desktop browser.
SR
Install Sound Runner as an app
Real app icon on your dock, home screen or start menu. Opens in its own window and runs with no internet.
/ 01 Settings
This browser can’t encode AAC natively. MP3 is available here and is accepted by every major transcription service. For .aac output, use Chrome or Edge.
/ 02 Add files
Drop broadcast WAV files, or a whole folder, here or click to browse
Drop your WAV files, or a whole folder, straight off the card.
2Convert
Encoding happens right here on your machine, timecode and metadata kept.
3MP3AACOutput
MP3 or AAC files come back, plus a zip automatically when it is a batch.
4Transcribe
Upload the small files to your transcription service and get to work.
5Done
Your original WAVs are still on the card, untouched, ready for conform and sync.
/ 05 Why it works this way
Fast and reliable
Every conversion happens on your own machine, so there is no upload queue, no server to be busy, and nothing to wait on.
Private and secure
Nothing is uploaded. Confidential dailies never leave the room, and there is no copy of your audio sitting on somebody else's server.
100% offline
Install it once and run the whole thing with no internet at all, in the truck, on location, or on a plane.
Works anywhere
Use it right here in the browser, or install it as a real app on your phone, laptop or desktop.
Your machine. Your files. Your privacy.
No uploads. No waiting. No risk. Convert with confidence and keep your dailies exactly where they belong, on your own machine.
Frequently asked questions
Converting WAV to MP3 or WAV to AAC for a transcription service, and what happens to your timecode and metadata along the way.
How do I convert a WAV file to MP3?
Drop your WAV files onto the box above (or click it to browse, or use the folder button to add an entire card), leave the output format on .mp3, pick a bitrate, and press Convert all. The MP3s are ready to save in seconds, and a .zip of the whole batch downloads by itself once the last file finishes. Nothing is uploaded and there is no sign-up.
How do I convert a WAV file to AAC?
Exactly the same way, except you set the output format to .aac before you convert. The .aac file is a real ADTS AAC-LC stream, so the extension matches what is actually inside it and every transcription service and ffmpeg-based pipeline accepts it as is. AAC encoding uses the browser's built-in encoder, which means you need Chrome or Edge for .aac output. In Safari or Firefox, use MP3, which every service accepts anyway.
Is it free, and do I have to sign up or install anything?
It is free, there is no account, no sign-up, no watermark, no file limit and no queue. You can use it right here in the browser, or install it as a real app on your dock, home screen or start menu, or download the single-file version and keep it on a thumb drive. All three are the same tool.
Are my audio files uploaded to a server?
No. Every conversion runs on your own machine, inside your browser, using the same encoders your computer already has. Your audio is never uploaded, never stored and never seen by anyone else, which also means there is no waiting for a multi-gigabyte WAV to crawl up to somebody's server. Confidential dailies never leave the room.
Does converting WAV to MP3 lose quality?
Yes, a little, because MP3 and AAC are lossy formats: they throw away data your ears are least likely to miss in order to make the file roughly ten times smaller. For transcription, editorial review and client copies that difference does not matter at all. For the finished mix or anything going back into a conform, keep the WAV. That is why this tool never touches your original.
What bitrate should I use for transcription?
128 kbps is plenty for speech and gives you a file about one tenth the size of the WAV. Go to 192 or 256 kbps if the audio is noisy, heavily accented, multi-speaker or a crowded room, and drop to 96 kbps only when you are fighting a hard upload limit. Bitrates from 96 to 320 kbps are available here.
Will this change or overwrite my original WAV file?
Never. Source files are opened read-only through the browser's file APIs and every output is a brand new file written next to nothing. The master WAV on your card or drive is untouched, byte for byte, and stays the master for conform and sync.
Does it keep the timecode from a broadcast WAV (BWF)?
Yes, and that is the whole point of this tool. The BWF TimeReference value is read out of the bext chunk and converted to real start timecode at the file's own frame rate, then written into the output file's tags and into an optional conversion report. Supported rates are 23.976, 24, 25, 29.97 drop and non-drop, 30, 48, 50, 59.94 drop and non-drop, and 60. Drop-frame math is done properly.
What metadata is preserved when I convert?
Start timecode, frame rate and the raw sample count, scene, take, tape and project, track names, originator and origination date, the mixdown that was used, and a SHA-256 hash of both the source and the output. It goes into the output file's own tags, and optionally into a .txt report you can read and a .json file a machine can read. That paperwork is the point: nobody can claim the timecode or the scene and take got lost in the handoff.
Can I convert a whole folder or an entire card at once?
Yes. Use the folder button, or drag a whole folder onto the drop zone. Subfolders are scanned, non-WAV files are ignored, duplicates are skipped, and the batch converts in order with an overall progress bar. When the last file lands, a .zip of everything downloads automatically.
Is there a file size limit? Does it handle large poly WAV files?
There is no size limit. Files are read in blocks rather than loaded whole, so multi-gigabyte poly recordings are fine, along with RF64 and BW64 files that are already past the 4 GB WAV ceiling. Files over 512 MB skip the source SHA-256 only, because of a browser hashing limit, and the report says so.
How does it handle poly files with isolated tracks?
You get two choices: the original L/R stereo mix exactly as recorded, or a mono mix folded down from those same two tracks. Both work from tracks 1 and 2, the mixer's own mix. Isolated tracks are deliberately never summed in, because that doubles up dialogue and gives a transcription service a worse file than the mix does. Whichever you chose is written into the tags and the report.
Should I send MP3 or AAC to a transcription service?
Either works. Every major service, Rev, Otter, Trint, Descript, Sonix and anything built on ffmpeg or Whisper, takes both. MP3 is the safest default and works in every browser. AAC is smaller at the same quality, which helps if you are uploading a long interview over a hotel connection or a hotspot.
Which browsers, computers and phones does it work on?
Any modern browser: Chrome, Edge, Safari and Firefox, on Mac, Windows, Linux, iPhone, iPad and Android. MP3 output works everywhere; .aac output needs Chrome or Edge. For big cards and long files, a desktop browser is more comfortable than a phone.
Can I use it offline, with no internet?
Yes, and this is worth setting up before you need it. Install it as an app from the card near the top of the page and it caches itself, so it opens and converts with no signal at all. Or download the single-file version: one HTML file you can email, drop on a thumb drive or keep in a folder on set, that runs by double-clicking it. No internet, no install, no account.
What is a broadcast WAV (BWF), and why do I only have WAV files?
A broadcast WAV is an ordinary WAV with extra chunks bolted on, mainly bext and iXML, that carry the timecode, scene, take, project and track names post needs to sync and conform. Location sound recorders write them by default, which is why a shoot can wrap with nothing but WAVs on the card. When a producer then asks for MP3s for transcription, this is the tool that makes them without dropping the information that makes those files useful later.
Sound Runner · timecode & metadata live in the output tags + sidecar report · the original WAV stays the master for conform/sync floridasoundman.com