In the U.S., Casino Gaming has retention requirements based on venue.
The NIGC (National Indian Gaming Commission) requires 7 days retention for all MICS-required (Minimum Internal Control Standards) cameras and 30-day retention of evidence files. Nevada Gaming Commission and State Gaming Control Board require varying retention times based on venue and camera function: 7 days for most cameras but 30 days for detentions and security interviews in casinos; 90 days for all cameras in "Gaming Salons". 3 days for other cameras.
Some states require Indian casinos to retain their cameras longer than the 7 days NIGC MICS requires. Up to 30 days.
Our future system will retain most cameras for 15 days, while cash counting and cages will be retained for 60 days. We never delete evidence clips. We have some stored going back to 1994.
I'm not aware of any maximum OR minimum legal requirements under Canadian or BC law (can't speak for other provinces). I know some INDUSTRIES have set GUIDELINES, although they're not hard-and-fast rules.
Video in the US, no limits Federally, I am not sure if any states have limits (NY doesn't)
Audio is a great question, again not a ton of this is set at a Federal level, and there are a dozen or so States that have different laws regarding ANY recording of audio, but I dont know if they address duration of holding it once it is legally recorded. I'm sure someone in law enforcement could clarify.