I bought the red iPod cable for my iPhone 4 but have now decided to go the SD card route, I can just leave it in the car and know it is always connected.
I spent yesterday evening testing with a 2GB SD card, I confirmed that MP3s work (as expected) but also that M4a files, copied straight out of the iTunes folder, worked too - something that I wasn't originally sure about. Both formats showed cover art and all was good.
Today I uploaded 8GB of music onto a new 32GB SDHC card and both MP3 and M4a files play perfectly..... however no album cover art!
I assumed that it might be due to the different SD card so I tested the 2GB card that I used yesterday..... same thing, no cover art?
99% of the images are below 500 x 500 and besides they worked yesterday, so image sizing isn't the issue.
When I view the files on the SDHC card with my MacBook or my Windows laptop I can see the artwork, so it has embedded ok. It even shows the image when Windows Media Player plays a track.
I'm baffled now...... any ideas folks?