Sony announced during their E3 presser that PlayStation 4 is getting a new media player app. It's now available in Europe, so just download it for free if you want it. You can enjoy music, photos and videos either from a USB stick or from your own server.
In the US PlayStation Blog they confirmed all the supported formats, and the list can be seen under the picture.
File Formats and Codecs
Video
MKV
Visual: H.264/MPEG-4 AVC High Profile Level4.2
Audio: MP3, AAC LC, AC-3(Dolby Digital)
AVI
Visual: MPEG4 ASP, H.264/MPEG-4 AVC High Profile Level4.2
Audio: MP3, AAC LC, AC-3(Dolby Digital)
MP4
Visual: H.264/MPEG-4 AVC High Profile Level4.2
Audio: AAC LC, AC-3(Dolby Digital)
MPEG-2 TS
Visual: H.264/MPEG-4 AVC High Profile Level4.2, MPEG2 Visual
Audio: MP2(MPEG2 Audio Layer 2), AAC LC, AC-3(Dolby Digital)
AVCHD: (.m2ts, .mts)
Photo
JPEG (based on DCF 2.0/Exif 2.21)
BMP
PNG
Music
MP3
AAC (M4A)