2017 Audi A3 vs SD cards

My new car has a fancy stereo from Audi / Bang & Olufsen that can play audio (and video!) off of SD cards. Awesome! So I loaded up a 128GB SDXC card with my music collection, inserted it, and watched it crash as it indexed. But it seemed to work anyway after rebooting. Only some music is missing.

Looking more closely I figured out music started being missing right around Johnny Cash. But nothing wrong with those Johnny Cash files, they work on a new card just fine. A bit more googling and head-scratching and I learned the Audi might only read 64GB of an SD card. This limit is baffling; the big limit on SD is 32GB, the SDHC format. The car’s manual explicitly says it supports up to 128GB cards. I found this other post that claims > 64GB cards work, but only with FAT32, not exFAT. There may also be limits on the number of files / directories / etc, but it’s vague.

Anyway, on my exFAT SDXC card everything after Johnny Cash is unreadable. At first I thought that was the 64GB limit but counting carefully really it’s like 69GB in. I’m also at about 9800 files before I hit the Js, so maybe it’s actually a 10,000 file limit?

Another mystery is the indexing system. It definitely scanned the SD card the first time it saw it, for several minutes before crashing. Now when I put the card in it doesn’t index it. I’m not positive if it’s detecting changes in the drive or not. (I think so?) Where is it storing the index? There’s a file on the root of the SD filesystem named “WMPInfo.xml” that it placed there, some Windows Media Player junk. But it’s only 296 bytes. The car has its own dedicated hard drive with a partition for a “jukebox” I can copy music to. Perhaps it has another partition for databases and stuff. It’s got a copy of the GraceNote database built in somewhere!