PDA

View Full Version : Bit-Rate 4/3 - 16/9



logic28
12-15-2007, 05:10 PM
Hi Guys,

I asked this question some time ago but nobody seems to have answered.

Just in case somebody missed it, I am going to post it again. Here goes:

As far as I am aware, the D1 sampling rate for VT4 equates to 173/177 Mb/s.

They don't specify though if that only applies to 4:3 aspect ratio or if it also covers the 16:9.

I assume it does by using the same screen resolution and simply adding the letter-box black lines totaling the same amount of data per frame.

But... the standard SMPTE specifies that SD-SDI should have a value of 277 Mb/s when recording in 16:9 format.

So, how does VT4 sample SD 16:9? And, is it different from selecting "working in 4:3 or 16:9" from the Preference panel?

In fact, what difference is there between the two since I haven't been able to find any reference about it in the manual and it doesn't appear to make any substantial changes to the platform?

I know somebody out there has already questioned this

Thanks,

Maz

rbartlett
12-15-2007, 05:49 PM
I believe you take the 177M figure and run that spec against 4:3 or 16:9 sources. 177M is the result of 8bit 4:2:2 uncompressed digitization. Or ~22MBytes/sec per D1 stream (prior to wrapping in RTV or AVI envelopes and prior to supporting more than 2 channels of audio).

The only difference between sources are in what pixel aspect ratio the same 720x576 PAL (or 720x486 NTSC) refers to. If your source is widescreen then the editing and preview mode in the VT needs to be 16:9 as the source is anamorphic (ie squished horizontally compared to traditional D1 rectangular pixels).

VT[4] doesn't furnish you with what you need to handle every aspect of standard def. ie Mixing 4:3 and 16:9 into a 16:9 product isn't the most straightforward requirement to find a solution for. Titles assume 4:3, there is no widescreen signalling (WSS) and DVEs assume target processing as 4:3 as of VT[4]. For just a few examples. VT[5] opens up more resolution and aspect ratio independence.

Adding letter-box isn't part of the digitization process. It is more for what you'd do to instruct the NLE part of the suite of your source properties and framing if you were editing in VT-Edit (VT[4]) or SpeedEDIT-VT (VT[5]).

The 270Mbps rate you've seen mentioned is in regard to SMPTE 259M-C for 625 line (PAL) when dealing with 10bit 4:2:2 data pumping the video of mux in a broadcast format (e.g. down an SDI cable). Bitrates vary depending on the dimensions and presence of audio, closed captions, timecode, and other sorts of metadata. VT is an 8bit YUV (Y'CbCr) system that restricts the I/O to 4:2:2 sub-sampling to and from real world devices (it has higher performance internally).

In a roundabout way, these answers have been given before but your question is quite original in nature. No bad thing really.

jsanfilippo
12-17-2007, 08:52 PM
Wow - I always feel really stupid by comparison when Richard posts. :)
And note that his profile says "amateur" videographer. LOL