Choosing capacitors for AD725 encoder
Input coupling caps are there primarily so that the internal DC clamps can find the black level and as such they can be X7R (I have used those for this purpose) although 1000pF C0G would probably be appropriate. 

The real advantage of C0G is the temperature coefficient (and Analog Devices video parts can be very susceptible to signal path variations due to thermal issues - I do not know of this is the case here).

The datasheet states:


  The inputs should be held at the input signal’s black level during
  the horizontal blanking interval. The internal dc clamps will clamp
  this level during color burst to a reference that is used internally as
  the black level. Any noise present on the RIN,GIN, BIN or AGND pins
  during this interval will be sampled onto the input capacitors. This
  can result in varying dc levels from line to line in all outputs, or if
  imbalanced, subcarrier feedthrough in the COMP and CRMA outputs.For
  increased noise rejection, larger input capacitors are desired. A
  capacitor of 0.1 μF is usually adequate.


So the larger capacitor (and 100nF is very common) keeps noise levels low.

For the output capacitor, keep in mind that the output is designed to drive 150\$ \Omega\$ so it is wise to keep the ESR reasonably low. Low ESR tantalums might not be appropriate as their capacitance rolls off quite quickly above a few 100 kHz although the large capacitance is for the low frequency components. As I have a lot of different reasons for not using tantalum devices in general, I have not used them in this particular scenario. 

AD does not have the best reputation for support from (at least the European) video support group incidentally.

I have used OS-CON devices for the output capacitors and they worked very well. These have ESRs on the order of &lt; 40 milliohms.

I don't really think 'audio grade' devices are necessary for clean video; they are optimised for performance in the audio spectrum which is only a small part of the bandwidth of a composite video signal.