BCSTM File

What are BCSTM files and how to open them

Are you having problems opening a BCSTM file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BCSTM files.

What is a BCSTM file?

A .BCSTM file is a BCSTM Audio file.

BCSTM is a streamed audio format used by Nintendo 3DS games to store soundtrack or background music with looping support. Files in this format are created by Nintendo's game build tools and played on the 3DS during gameplay to provide background sounds or music that can repeat seamlessly. One common use is for "bgm.bcstm" files in 3DS themes, which supply the theme's music in the system menus.

These files typically contain one or more audio streams encoded using one of several possible sample formats (such as DSP-ADPCM, IMA-ADPCM, PCM8 or PCM16), along with metadata that governs looping behavior, channel count, sample rate, and track layout. Decoding tools like ISA/Sound Editor and vgmstream can read the format and extract or convert the audio to standard formats like WAV for editing or playback elsewhere.

On the 3DS, BCSTM files are often stored inside BCSAR archives under "romfs:/sound/stream/" or included as theme music files (named "bgm.bcstm") in the Theme BGM slot. They are distinguished from similar formats by their INFO, SEEK, and DATA blocks.

These files begin with the ASCII signature "CSTM" at offset 0, followed by an INFO block with "INFO" at offset 64. Other internal fields define things like encoding type, loop start and end points, channel info, and sample block layout.

How to open BCSTM files

Important: Different programs may use files with the BCSTM file extension for different purposes, so unless you are sure which format your BCSTM file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 23, 2026

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