If you are talking about converting broadcast digital signals to analog, forget it. As pointed out already, the digital signal if far more than just a digitized version of the analog one. It will be an encoded stream which also carries program information and quite likely more than one program stream. It will also be encoded as OFDM, QAM, QPSK or another transport system and the actual video will be compressed using MPEG or H264. It's a very complex signal!
The DAC0808 is also far too slow to be able to produce the video bandwidth you require. Ideally, you want a DAC that can produce a signal containing components up to at least 6MHz for standard definition and about 12MHz for HD. The DAC0808 is of no use beyond about 3MHz.
Brian.