You have a couple of issues here. Your SDI or HDMI outputs out of the switcher ia high definition only. The RCA inputs on your dvd are SD (standard definition) only. These two will not speak to each other without external conversion.
The easiest way is to get an HDMI to SD downconverter that has the necessary connectors to allow you to do this. I have used the Blackmagic Design Mini Converter UpDownCross Converter to do this. You have to adapt the cables to RCA style to get the audio in.
The second issue is that by definition DVD is not HD in terms of quality so expect a downgrade. You cannot buy a DVD recorder that will accept digital inputs directly (SDI or HDMI) due to HDCP (content Protection). The only way to record a blue ray disc in original HD resolution is through a computer generated DVD.
Hope this helps.
Jim Brown
M&M Productions USA
Oak Ridge, TN