Free Online BRSTM Converter & Player — BGM Box

What is BGM Box?

BGM Box is a free online BRSTM converter and player designed for Nintendo gamers, modders, and emulator enthusiasts. Whether you want to replace the background music in Mario Kart Wii, add custom tracks to Super Smash Bros. Ultimate, or simply listen to a BRSTM file you downloaded from the community — BGM Box gives you everything you need in one place, right in your browser.

Unlike traditional desktop tools that require installation, command-line configuration, or manual hex editing, BGM Box runs entirely in your browser powered by vgmstream, the industry-standard game audio decoding engine. That means you can drag in virtually any audio format from any game — ADX from SEGA titles, HCA from mobile games, FSB from PC games, WEM from Switch games, ATRAC3 from PlayStation games, XMA from Xbox games — and convert them directly to BRSTM, BCSTM, or BFSTM. No intermediate tools. No format hopping. No downloads. No sign-ups. No server uploads — your files stay on your device.

What Nintendo Audio Formats Are Supported?

BGM Box supports all three major Nintendo audio container formats across console generations:

• BRSTM — Used by Nintendo Wii games. The most popular format for custom music in Mario Kart Wii, Super Smash Bros. Brawl mods (Project M / Project+), and Dolphin Emulator.
• BCSTM — Used by Nintendo 3DS games. Compatible with 3DS homebrew, custom HOME Menu themes, and Citra Emulator.
• BFSTM — Used by Wii U and Nintendo Switch games. The newest format, supporting higher-quality audio codecs and up to 8 channels. Perfect for Super Smash Bros. Ultimate mods and Yuzu/Ryujinx emulators.

Why Use an Online BRSTM Converter?

Before BGM Box, converting audio to BRSTM meant downloading specialized Windows-only tools like BrawlBox, BRSTM2WAV, or LoopingAudioConverter. These tools work, but they come with serious downsides:

• You have to download, extract, and configure software for every computer you use.
• Loop point editing typically requires manual hex editing or command-line tools — no visual feedback.
• Multi-channel BRSTM creation (for dynamic game music) is extremely tedious in traditional tools.
• Mac and Linux users are often left without any native options.

BGM Box eliminates all of these problems. The converter runs in your browser on any device — Windows, Mac, Linux, even ChromeOS or a tablet. The visual loop editor shows you exactly where your loop points land on a waveform slider. Multi-channel audio (up to 8 channels) is handled automatically. And because all processing happens locally via WebAssembly, there are no file size caps and no privacy concerns.

What Can You Do With BGM Box?

Here is what makes BGM Box a complete Nintendo audio toolkit:

• Convert MP3 to BRSTM — The most common use case. Turn any MP3 song into a Wii-compatible BRSTM file with custom loop points in seconds.
• Convert WAV to BRSTM — Use lossless WAV source files for the highest possible audio quality in your final BRSTM.
• Extract BRSTM to MP3 — Got a BRSTM file and want to listen to it on your phone? Decode and download as standard MP3.
• Create BCSTM for 3DS — Build custom audio for 3DS homebrew games, custom themes, and Luma3DS layeredfs mods.
• Create BFSTM for Switch / Wii U — The newest format for modern Nintendo consoles. Higher quality, more channels.
• Play BRSTM Files Online — Our built-in player decodes BRSTM, BCSTM, and BFSTM files with a real-time FFT spectrum visualizer and multi-track support. No software needed.
• Edit Loop Points Visually — All conversion tools include a visual waveform slider where you can drag to set precise loop start and end points. No more guessing sample numbers.

Decode 100+ Game Audio Formats — Encode to BRSTM/BCSTM/BFSTM

vgmstream is the industry-standard decoding engine for video game audio. Only BGM Box brings its full power to the browser — with zero installation.