A recent post on the (wonderful) “What If?” website entitled FedEx Bandwidth got me to thinking about a calculation I did some time ago, that for the life of me I can’t find, so I’ll have to re-generate.
What’s the equivalent download bandwidth of a Netflix DVD subscription? You know, the option Netflix actually started with: they ship you a DVD and you ship it back, with the simple caveat you can only have one DVD “out” at a time.
First we have to assume perfect timing:
- Day 1: Netflix ships your DVD
- Day 2: You get your DVD, watch it and ship it back
- Day 3: Netflix gets your DVD and ships you a new one
- Repeat, for an entire month.
Note several assumptions: you can ship the DVD back on the same day you received it. Typically that means a trip to the post office to drop it in the mail, since the postman’s already visited you once to deliver the disc in the first place. It also means you watch it as soon as you get it. Realistically this means you rip it to watch later, but we’ll stay legal – if a little busy – to keep this all above board.
Work the sequence and you’re looking at a disc every other day. (Like I said, in a perfect world.)
But wait … the post office isn’t available every day, and we need to account for that. Right now they deliver only 6 of every 7 days, skipping Sundays. In August of 2013 they’re planning to drop Saturday delivery as well to make that 5 of every 7. So we’ll need to account for that. Since most of this is basically approximations and guesswork, I’ll simply take the final result later and multiple by 6/7ths and 5/7ths to account for what we might refer to as “network down time”.
Now, there’s a wide variety in the amount of data that a DVD might hold. Some movies are significantly smaller than others, while some are not only lengthy films but also come packed with bonus features and the like.
Rather than try and figure all that out, I’ll simply assume a common “large” capacity double-sided two layer DVD which can hold 9.4GB, or approximately 9,400,000,000 bytes. 8 bits to a byte turns that into 75,200,000,000 bits.
75,200,000,000 bits every two days. 48 hours, 60 minutes per hour, 60 seconds per minute and we get…
435,185 bits per second.
We’d probably call that 435kbps, or just under half a megabit per second.
But wait! We still have to account for the postal service’s delivery schedule. The net result:
- Until August: approximately 373kbps, with 6 day a week delivery
- After August: approximately 311kbps, with 5 day a week delivery
Of course you could double your “bandwidth” by signing up for Netflix’s two discs at a time plan, or perhaps one of their Blu-ray options.
At least in this regard most broadband connections (I’d say 1.5mbps, aka 1500kbps, or better) are still faster than Netflix.
Just remember that assumes you’re using the connection 24 hours a day, 7 days a week to transfer the data. It doesn’t mean you can necessarily stream video – that requires you be able to download a 1 hour movie in no more than one hour. The calculations above send you one movie every two days.
Actually streaming standard definition (SD) at DVD quality requires something more than 1.5mbps. (The good news is that most streaming videos are nowhere near DVD quality, but even so 1.5mbps is pushing it.)