External Recorders, Bit Rates, and Sampling
Posted 10 October 2011 - 06:17 AM
I have searched this forum about the following question but have had no luck finding answers:
Facts: Using an Ag-af100 with a nanoflash external recorder the bit rate goes from the standard 25mbps up to 250mbps. The colour sampling rate goes from 4:2:0 to 4:2:2.
Questions: having not observed any noticeable difference between the two images, standard and nano-infused, do external recorders coming through an HD SDI port somehow bypass the cameras compression settings and create a souped up image? Or does it take the cameras compressed image and digitally ramp up the bit rate?
How does the bit-rate actually affect the overall image?
It is all just a bit confusing and I thank you in advance for your answers and patience for my ignorance.
Posted 10 October 2011 - 06:38 AM
Advantages of a less compressed image are that a 4:2:2 colour space is easier to key for chroma key stuff. The milder compression means the footage is easier for a colourist to grade without the image going bad. Also less compression means less video compression artifacts.
If you are trying to compare footage you have seen on the internet, keep in mind it has all been compressed to hell before uploading to youtube or Vimeo or whatever anyway. Also sometimes the differences can be subtle, and lastly, some people are by this point, so used to seeing compressed video, they don't notice any of the artifacts.
Edited by Freya Black, 10 October 2011 - 06:39 AM.
Posted 10 October 2011 - 08:34 AM
Some broadcasters specify an absolute minimum bitrate for certain types of acquisition, often 50Mbps.
This is idiocy, because you will get better pictures with (for instance) h.264 at a given bitrate than you would with MPEG-2, and you'll get better pictures with a good encoder that costs a lot of money and consumes a lot of power, as opposed to one that's cheap and runs on double-A batteries. It also puts things like Panasonic's P2 format in an interesting position because although the bitrate for that format is commonly taken to be 100Mbps, at 24fps it's actually only recording 40.
Given that various codecs can also create problems with compatibility in postproduction, personally I prefer to get everything into uncompressed as soon as possible. The hardware required to handle it is no longer exotic. Recent developments such as Blackmagic's Hyperdeck Shuttle recorder make this so cheap and easy it almost seems churlish to turn it down. At some point, compression is just an excuse.
Posted 10 October 2011 - 10:03 AM
Posted 10 October 2011 - 01:39 PM
I think once you get up into the hundreds of gigabytes it invariably boils down to an LTO solution if you aren't just willing to splurge on heaps of flash. I tend to engineer data handling to deal with the worst feasible case, working away from civilisation somewhere with at best a 12V power supply available. Of course if you're willing to assume more support than that, it gets easier.
Posted 28 October 2012 - 01:21 AM
You really should look at native footage shot on a camera. I have a trusty Sony Z5 and went from HDV tape to using it with an Atomos Ninja. The difference is incredible. Exactly as Freya says, the coloring in Final Cut is solo much better. You can shoot at nearly a stop slower and still pull tons out of the lowlights. Made the Z5 with 0.5 lux into a midnight wonder cam... Well almost.!
Best £600 you can spend on a small-bitrate camera... And you are HD channel ready should something you shoot get used!