Recording File Sizes D1/960h Vs. TVI

I am planning on switching over to TVI camera systems. Question I have is about Hard Drive sizing. Currently, I use a 1 TB drive for my 4/8 channel D1/960h systems. I generally set mine to record motion only, with a 5 second pre and post record, and mask the areas where traffic goes by, trees, bushes, etc. On this setup, I have been able to have an 8 channel 960h with 8 Sony SSA 700TVL cameras keep the recordings for at least 2 months in a 9-5 business environment. In switching over to TVI, how much larger are the file sizes? I use the WD Purple Surveillance hard drives, and the cost difference between a 1 TB and 2 TB is about $25. I deal with mostly cheap-ass customers, so I was wondering in the 8 Channel TVI, would the 1 TB be ok to use, or would it be better to use the 2 TB. Generally, I like to keep recordings for at least 6 weeks, just in case there are any issues that did not get noticed right away.

Thanks!

TVI is a video format, not a resolution. With TVI you would normally record at 1280x720 or 1920x1080. Recording time depends on bitrate, not on resolution. But normally if you use double the resolution, you would want to use double the bitrate (when using the same frames per second).

So, if 960H is 960x576 = 0.55 megapixels, and you record at 1280x720 = 0.92 megapixels, from there you can make some numbers.

OK... so basically, I am looking at a min of 40% increase in file sizes then. So, I would guestimate on motion only about 3-4 weeks on 8 Ch 1TB and 16 Ch 2 TB. Still should be plenty, but I can give the customer the option on 1 TB, 2 TB and 4 TB depending on how long that want to keep the recordings.

Thanks!