TweakTown posted a review on Western Digital's WD TV HD Media Player

You could think of it as a DVD player without the optical DVD drive and a home theater PC without the full functionality of a computer. It really is just that - it doesn't come with any internal storage and sadly no Ethernet networking support, but it does include two hi-speed USB 2.0 ports, which allows you to hook up two external hard drives or USB flash drives which use a FAT32, NTFS or HFS+ (no journaling) file system.

The WD TV allows you to view photos, listen to music and watch movies on your TV. We have seen several devices like in this part, but none as good as this one. As for photos, WD TV supports JPEG, GIF, TIF/TIFF, BMP and PNG file formats. As for music, it supports MP3, WMA, OGG, WAV/PCM/LPCM, AAC, FLAC, Dolby Digital, AIF/AIFF and MKA file formats. As for movies, it supports MPEG1/2/4, WMV9, AVI (MPEG4, Xvid, AVC), H.264, MKV, MOV (MPEG4, H.264),MTS, TP and TS file formats. You will need to update your WD TV firmware to version 1.01 for all of these formats to be supported. Ours came already updated, so you may or may not need to depending on how long yours has been sitting around in the warehouse.

Western Digital's WD TV HD Media Player - Video Review