Plays and records audio, including ACC and MP3 files.

To put music on there you can either just chuck it in the root of the SD card, or make a folder/s there. When listing music in the software it will first show you all folders together that contain music, even if they're subfolders. So don't bother organising stuff by putting artists in their own folders, as a folder without music files in it won't appear in the listing.

According to Nintendo's website the following formats are supported:

• AAC files with .m4a, .mp4, and .3gp extensions
• MP3 files with .mp3 extensions, bit rates of 16–320kbps, and sampling frequencies of 32–48kHz

So pretty standard, but no OGG >:-|

You can also make a small playlist of songs that will be used for StreetPass. I only found out about this is March 2020, so not sure what exactly gets shared, but it looks like it makes a 'top 10' list of songs based on that, and makes a note when your tastes match with other people's.

※ Exporting files for the 3DS on the Foobar2000 page.

There're lots of fun features when playing back music!

• You can use the L and R buttons to play along with the music, and select different instruments to play by tapping on their icons.
• You can, independently, change the pitch and speed.
• View a bunch of 3-D visualisations, some you can control with the analogue stick.
• Apply the filters that add echo, kinda remove the vocals, replace the song with '8-bit' instrumentation, and make it sound like it's playing on an old radio.
• Loop certain parts of a song, as well as the usual repeat, and random features.

Bunch of minigames you play with Miis you've got via StreetPass.

• ftpd - Simple FTP server for transferring files without having to turn the 3DS off and remove the SD card.
• JK's Save Manager (JKSM) - Export and import save data.
• Thenaya - Writing and ripping amiibos.
• Pretendo Network - Homebrew effort to replace the shut-down Nintendo Network.

It's possible to do screen capture over the network, without the need for special hardware. Framerate is low, but it's neat.

• https://gbatemp.net/threads/3ds-screen-recording-without-a-capture-card-ntr-cfw-method.423445/

• List of 3DS homebrew page on the GBATemp wiki.

On Linux I use mkfs to format the SD card. Guides say you need to format with a block size of 32kB/32768B, but mine is 4kB/4096B and seems to work fine? The DS emulator gives a warning, but otherwise works fine. Does seem a little slower than the card that came with the 3DS? Haven't had any luck with the recommended block size. Very likely I just don't understand disks stuff enough.

# mkfs.fat [disk]

Moving stuff to a new card is easy, just copy the directories over.

Okay, I've since reformatted it to 32kB, based on a guide I was reading to fix another problem—thought I may as well:

1. lsblk to list devices, note NAME
2. Unmount the disk sudo umount /dev/[NAME]
3. Format with 32KB cluster size, FAT32 (FAT16 for small card):
   • 2GB or lower: sudo mkfs.fat /dev/[NAME] -s 64 -F 16
   • 4–128GB: sudo mkfs.fat /dev/[NAME] -s 64 -F 32
   • 128GB or higher: sudo mkfs.fat /dev/[NAME] -s 128 -F 32

※ You can check block size with stat -fc %s [PATH] or stat -fc %s . from a directory on the disk.

• 3ds.hacks.guide
• Dumping Games to SD Card
• Regarding dumping - Getting saves.

• Notes on 3DS Games
• nintendo_3ds_hacking