Understanding bitrate capture vs delivery

[John Rofrano]

[John Hughes] “So I’m learning that the max bitrate of say Blu-Ray is around 40Mbps but that’s more for pressed Hollywood media and that standard Blu-Ray is about 20-25Mbps. If I am delivering the final product as a Blu-Ray, it seems then that I may be losing a lot of quality going from source to delivery (50Mbps to 20ish Mbps)?”

Quality is relative. Will you see a quality loss? It is possible because you have seen the original, but then again you might not. Will your audience perceive a quality loss? Absolutely not! It will look like great HD to them. Blu-ray was created back when high quality HD was 25Mbps. The days of DVD where a acquisition formats didn’t change for 10 years is over. From here on out, you will never be able to deliver in the quality of your acquisition because formats are changing too fast for players to keep up. Just accept it.

[John Hughes] “I’ve also heard of people using higher bit rate renders for posting video online. Is online video the best medium available from which to post the highest quality content? “

The majority of the world doesn’t have the bandwidth for video bitrates that high so unless you only want to appeal to people in large metropolitan areas. Forget about that too.

[John Hughes] “And can someone help me understand 2-pass vs 1-pass encoding? Is this just for encoding video that goes online and not with DVD/Blu-Ray media?”

1 pass encoding makes an educated guess at how many bits it can use for each frame in order to stay within the average. Two pass encoding make an initial pass taking note off exactly how many bits each frame needs. Then it makes a plan on how to best allocate the bits given the average rate, and then makes a second pass where it encodes each frame at exactly the bits it needs (no guessing). Two Pass yields higher quality for a given average bit rate. This applies to DVD, Blu-ray, on-line, whatever.

~jr

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