FORUMS: list search recent posts

Is a capture and playback device a passthrough or a pitstop?

COW Forums : Apple Final Cut Pro Legacy

<< PREVIOUS   •   FAQ   •   VIEW ALL   •   PRINT   •   NEXT >>
Frank Black
Is a capture and playback device a passthrough or a pitstop?
on Dec 23, 2011 at 4:10:23 am

Hi guys,

Some of you already know that I'm researching the depths of what a capture and playback device does WHAT but that I'm looking for "precise" answers in a language a 2nd grader -- me! -- would understand.

Anyway -- I've been going in circles for 2 and half weeks -- no lie. I have so much in notes -- in word, in notepad, on paper, in emails, IN MY HEAD -- that I need to be UNCOMPRESSED!

I feel like all the answers are in my notes (so many notes). But the dots aren't connecting, and part of the reason is that I'm getting opinions that seem to contradicting but in all probability are most like just not "sensitive" enough. The other part of the reason is that I'm a second grader!

The dots aren't connecting because there actually are "holes" in the lines at the beginning and end the dots are. These holes are cause by the two "parts" mentioned above. I'm stuck MAINLY on one thing! And I need an a "sensitive" answer!! -- not an industry answer! I need (and I say need respectfully) an answer sensitive the level of my mind's current capacity not to shut off the moment an unfamiliar term injects it with fear and doubt.

So here's where I'm stuck (and there's gotta be a simple way to FULLY explain this):

1. why do we say that a cap and play device transfers uncompressed when a camera compresses the data when recording it, and since the camera's decompression doesn't fully restore. a full answer if possible. i will remember your name forever. full meaning something like this (though this probably wrong): well, a camera compresses it, then a cap and play connects to it via sdi, a button is pressed and a camera begins playback, and another button is pressed, and the cap and play sucks the wind out of the sdi and the sdi vacuums the footage out of the camera's playback (yep, takes it right off the LCD), and then it takes the data, encodes it, and shoots it thru a thunderbolt pipe into a mac. oh ye and by the way -- the playback was uncompressed. we call it uncompressed because the playback just orders the lost data to come out where it has fled to and get back in line to form a full original file in all its megabytes, and the guys that aren't coming back -- well we won't even notice they're gone. and so and so. (sorry for getting carried away. thanks if you're still with me. help!)

2. when does the camera decompress -- in playback or when you press the magic "decompress" button.

3. how do aja Io, BM UltraStudio 3d, and MXO2 transfer? does it serve as a passthrough or a pitstop? does it say: hang on data! cant go to the mac yet! we must do something to you first. we must: encode? decode? x? y? z?...

4. do all of the three machines mentioned above capture from playback only?


thanks. i'm in debt to you already if you've read this far.


val


Return to posts index

Jeff Meyer
Re: Is a capture and playback device a passthrough or a pitstop?
on Dec 28, 2011 at 1:41:39 am

I'll admit to having a difficult time understanding what you're trying to figure out, but I'll attempt to talk around what has you confused.

1) Most cameras do not record an uncompressed data stream. Uncompressed video is extremely large, so often cameras will use a codec that throws some information away - compresses - to drop the size of the data stream and to fit more onto the card/tape/drive.

Once recorded into a compressed medium it is possible to to play an uncompressed stream of the compressed data. For example, you could shoot on a DSLR, transcode it to uncompressed/animation and play an uncompressed stream out, but you'll be playing a perfect copy of the compressed copy. It's like starting with a 1,000 pixel (camera RAW) wide image, making an 800 (camera recorded) pixel wide copy, then making a perfect copy of the 800 (uncompressed transfer of camera recorded playback) pixel image. It doesn't have all of the detail the 1,000 pixel copy, but it has all of the information of the 800 pixel image.

2) Think of camera playback as converting data to a video stream rather than than decompressing. The camera compression at recording isn't lossless compression like a .zip file, it's lossy compression like making .mp3 files.

3) Interfaces (AJA, BlackMagic, etc.) are just that, interfaces. They take a video stream and convert it to a data stream that can be seized by a computer as a file, or the opposite.

4) I can't say that I understand this question. If you shoot on a digital camera that records to a card you should capture from the card, not through playback. This method is lossless relative to what the camera recorded. If you captured onto a tape you should capture through an interface (AJA, BlackMagic, etc.) or firewire if the tape was DV/HDV. That said, you could route/connect a camera or a switcher into a deck or a computer I/O and capture, at which point it isn't capturing playback.


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2018 CreativeCOW.net All Rights Reserved
[TOP]