• Sound card
  line in, mic in, multichannel in, digital in, on-board DSP
• Capture card
  TV: audio, video, data
• Firewire/USB
  video camera movie: audio, video, data
  digital cameria mini-movie: audio, video, data
• Network card
  streaming audio signal, streaming video signal
• Graphics card
  rendered raw video (T&L, OpenGL), TV-in (see Capture card)
  encoded video (hardware compression), raw video (hardware decompression)
• Hard disk/RAID
  encoded audio, encoded video, raw audio, raw video
• Disc media
  CD audio, DVD audio, VCD video, SVCD video, DVD video
• Software
  real-time audio generation/effects, real-time video generation/effects

I'd add:

• Metafiles
  playlists, meta redirectors (.ASX, .RAM, ...)
• Composite files
  things like Flash pages, or some parts of MPEG4 streams that are programmable