Quote:
Originally Posted by ManosHandsOfFate
And don't forget bandwidth caps. The 250 gig per month that Comcast allots me isn't going to allow me to stream a lot of Blu-Ray quality movies.
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Actually, 250GB is quite a lot. Note that I'm not necessarily supportive of any cap, but as far as caps go 250GB is a good number to choose.
As for streaming a blu-ray quality movie, that really depends. First, let's make some assumptions:
- The average movie length is 2 hours (120 minutes). While movies have been growing in length (I hate 3+ hour long movies!), there are enough 80 and 90 minute movies to compensate for the average.
- Blu-Ray movies often waste bitrate because they can. When you have 25GB or 50GB of space to work with, who cares if you use a constant bitrate rather than constant quality (variable bitrate)? For streaming, bits are precious. Depending on the movie, a 30,000kbps constant bitrate movie will look good with as little as 8000-10000kbps bitrate. Let's be generous and call it 15,000kbps average.
- Sound costs much less in terms of bitrate. Many blu-ray movies will use an uncompressed audio track, but again that's just a factor of having space to burn. For this comparison, I'm going to assume a 1500kbps DTS Surround soundtrack. That's 10% of the video bitrate, and gives excellent audio quality.
- I'm completely ignoring special features, multiple language soundtracks, commentary tracks, etc. All I'm considering here is the main feature and a single audio track in the language of your choice.
So, let's math.
Video + audio bitrate = 15,000 + 1,500 = 16,500kbps. Note that's in
bits not bytes, so let's divide that by 8 = 2062.5 KB/s, or just over 2MB/s. Let's round to 2MB/s. There are 60 seconds in a minute, so that's 120MB per minute. Using our previously stated 120 minutes per movie, that's 14502 MB per movie, or 14.2GB. With a 250GB cap, that's 17.6 movies you can watch per month. That seems like quite a lot to me. I have a hard time watching 2-3 movies per month (I watch considerably more TV, but we're just talking about movies here -- we need different assumptions and calculations for TV). Also, that assumes you're using your network connection only for streaming TV, so let's drop that number down a bit. Let's call it 15 movies at 14.2GB per movie. That's 213GB, leaving a healthy 37GB for everything else.
All of the above assumes you can even stream 16,000kbps. My Comcast connection can (I've got the 20Mbps plan, and I can actually do closer to 25Mbps sustained), but what do you do if you have the 12Mbps plan, or have slower DSL?
tl;dr: You have to try really, really hard to go over 250GB per month.
PS, If you want to do the math for other types of video, using the following:
- HDTV tops out at 20,000kbps, but is also MPEG2 which is much less efficient than other codecs. Comcast's HD is closer to 13,000kbps. You can reliably reduce that by at least 50% (and closer to 75%-90% -- I routinely compress MPEG2 HDTV recordings to ~2500kbps without any noticeable loss in quality), call it 5-7,000kbps. Audio is generally 384kbps AC3.
- TV shows tend to be 42-44 minutes per "hour", or 21-22 minutes per "half hour" (yay for ads!).
- If you don't need 1080p and are fine with 720p, the 15,000kbps number we used before can be reduced to 5,000kbps or less without any noticeable loss in quality. For comparison, Netflix's 720p streams are 3000kbps or 3500kbps, depending on the title.
- If you're fine with Dolby Digital 5.1 and don't need DTS, AC3 caps out at 640kbps.
In other words, there are plenty of ways to reduce bitrates without sacrificing much (or any) quality. The 14.2GB 1080p video we calculated above could be as little as 3.6GB using 3500kbps 720p video and 640kbps AC3 audio. You could watch over 70 of those before reaching the 250GB cap.