Whenever I speak in public about streaming production, I try to back up my recommendations with file parameters gathered from prominent media and corporate sites. Here are some file statistics gathered for a series of sessions that I taught this spring and summer.
Information from the first slide was gathered from about 50 corporate and media sites, which I divided into three categories based upon the total pixels in the frame. Conservative video is under 100K, Midrange under 200K, and Aggressive over 200K. There are multiple important take aways.
First, note that the aggressive broadcasters stream at a combined audio/video data rate of about 960 kbps. These are sites like ESPN, CNN and others who wouldn’t use those rates if the majority of their target viewers – in businesses and at home – couldn’t retrieve and play the file smoothly. If your video is stuck in the 300 kbps range because you’re concerned that your target customers can’t retrieve it, it may be time to rethink this policy.
Second, note the last column, which is bits per pixel per frame, essentially the data rate allocated to each pixel in the frame. Note that it’s up around .2 in both conservative groups, and much lower in the midrange and aggressive groups. This reflects a couple of realities. First, to some degree, codecs work more efficiently with larger resolution files than smaller resolution files, and you don’t need as high a data rate to produce the same quality. So, if you decide to boost your video resolution, you don’t need to increase your data rate linearly to maintain the same quality.
Secondly, some of these conservative producers are producing at a higher data rate than necessary.My rule of thumb is that irrespective of resolution, if your bits per pixel per frame is higher than .1, you may be producing at too high a data rate and should experiment with lower rates. This is reflected in the chart below.
As an example, ABC publishes one HD file of their prime time show Castle at .076 bits/pixel/frame, and the quality is flawless. Perhaps Sports Illustrated might need to be much higher for some of their video files, since they publish lots of high motion sports videos, but if I was in charge of encoding at CNN, TigerWoods.com and Apple, I’d be experimenting with lower rates, and I’ll bet I could achieve very similar quality levels at much lower data rates.
How do you compute bits per pixel per frame? Divide video data rate per second by (frames per second x video height x video width). Or, download the invaluable and free video utility MediaInfo, which works on Mac, Windows and Linux computers, and displays that info in the file analysis. Here’s a link to the download site.
Otherwise, if you’re thinking about reconfiguring your own video streams, hopefully you’ll find what other sites are doing helpful information.