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

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Frank Black
Is a capture and playback device a passthrough or a pitstop?
on Dec 23, 2011 at 4:07:44 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


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Gary Bettan
Re: Is a capture and playback device a passthrough or a pitstop?
on Dec 23, 2011 at 2:20:33 pm

First - why do you think you need uncompressed. For 99% of video editors, that represents nothing but a waste of disc space. Most editors use either an intermediary CODEC like Apple ProRes or Avid DNxHD. Today's latest NLEs also support native file formats such as XD CAM, P2, DSLR and AVCHD. While these formats require a faster computer to edit, they deliver the same outstanding image quality as the device that you used to shoot with.

You made an excellent point about compression. Your camcorder compresses the video into it's file format while you shoot. Once it is saved to disc, it is compressed. So running it out uncompressed does not make it magically better.

Today's workflows are file based. You simply transfer the files from the media it was recorder on into your computer and then edit. Some programs such as FCP7 require you to encode the files into ProRes before you can work with them. As I said earlier, Adobe and Avid now edit these files natively.

So why do you still need I/O hardware?

  • For playback in full res. I use an MXO2 Mini and output via HDMI to a Sharp Aquos LCD HDTV. Directly from the timeline. In full HD resolution.



  • Sometimes I do have to capture. It may be because i get footage form a non file based camcorder. Or there are times when I do really need uncompressed footage, not for my whole project, but for a segment. Perhaps I'm doing a lot of green screening and composting in After Effects; or a multi-layered segment with tons of filters and efffects; or just a clip that for whatever reason, the compressio
  • n plays havoc with. So I capture it via HDMI and it works better.

  • If you integrate with SDI based workflows, then you want a capture card that supports SDI. Look for upconvert/downconvert and cross convert features. That is what separates the different cards. For straight HD capture, you'll find they all offer pretty much the same quality.


  • I hope this helps. I suggest you give us a call 800 323-2325 and talk to one of our techs. We can help guide you towards the right products and workflows for your budget.

    Gary

    COW members get 5% OFF with Coupon COW5OFF

    http://www.videoguys.com 800 323-2325 | We are the video editing and production experts!


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    Frank Black
    Re: Is a capture and playback device a passthrough or a pitstop?
    on Dec 29, 2011 at 2:42:19 am

    Hi Gary, I just read your response again and was real glad to read the 3rd to last paragraph-- it helped me with something I'm researching further. Thx


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    David Eaks
    Re: Is a capture and playback device a passthrough or a pitstop?
    on Dec 23, 2011 at 4:57:28 pm

    I'll try to answer to the best of my knowledge and in an understandable language, if anything is fundamentally wrong or misleading I ask the experts to please correct me.

    [Frank Black] "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"

    It "can" do uncompressed, but playing back a compressed format from a camera's internal recording is not uncompressed.

    When you record with a cameras built-in recording method, the video gets compressed... forever. Information is PERMANENTLY LOST. When you play the video back to capture, it does not magically become uncompressed. The video is played from the compressed file, then you capture it into the codec of your choice. During capture you do not regain the "lost information", you simply take what the camera compressed and re-record it into another format that is better for editing.

    The compressed file from a camera is hard(er) for an NLE to work with, that's why you capture to a different codec that is better for editing. Also this is why the "editing codec" is a larger file than the "recording codec", because the editing codec is less compressed. Again, you do not magically regain any information (or in other words quality) when capturing to a better codec. You just change the compressed video into a less compressed form for editing, the quality of the video is not improved in the process. You end up with the same quality as the original recording, but in a form that is easier for the computer to handle.

    To capture "uncompressed" you would record from the HD-SDI output from an HD camera to an "uncompressed codec".

    It's like this-
    Light goes into the camera lens and is focused on the camera's sensor, forming the image for your video. From the sensor the signal goes two ways. One way is to the cameras internal processor to be compressed and recorded, the other is to the SDI out. This is where you get an "uncompressed" signal. Uncompressed meaning that the signal is at the camera sensors "native" quality. However good your sensor is, that's what you get.

    So, the video from the camera sensor bypasses the internal recordings compression, is output from the SDI and is ready to be recorded or captured.

    You "could" record the uncompressed signal with an I/O device (I/O = In/Out = Capture/Playback device) to an Uncompressed codec but that produces HUGE files and is most likely far from necessary quality-wise (not to mention the cost of operating in an uncompressed workflow). A much more feasible option is to capture the uncompressed signal to a highly efficient codec that retains lots of information without creating too big of a file size, namely Apple Prores or Avid DNxHD.


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

    It doesn't decompress and magically playback the full-quality uncompressed video. Video compression is not like compressing a word document. Let's say you compressed a word document into a smaller file size, emailed the compressed file, then the recipient uncompressed the file, all of the words will be there as expected. When video is compressed, parts of it are lost forever. Fortunately, with good video compression and depending on your needs, you might not even notice the lost information.


    [Frank Black] "how do aja Io, BM UltraStudio 3d, and MXO2 transfer? does it serve as a passthrough or a pitstop?"

    Of these, I can only speak to the Matrox MXO2 LE from actual experience. The video signal goes out of the camera through the MXO2 and into the computer for capture. The I/O device just feeds the signal to the computer. During capture the MXO2's outputs are active, so you can send the video/audio to a monitor or other device at the same time as capturing on the computer. If that is what I think you mean by passthrough, then yes it is that. It can also up/down/cross-convert the incoming video before it goes to be captured, if this is what you mean by "pitstop" then yes, it is that too.


    [Frank Black] "4. do all of the three machines mentioned above capture from playback only?"

    No, you can capture the signal live from the camera (again I'll only speak to the MXO2 specifically). I do it all the time with my MXO2 LE and 17" MBP. Capturing 1920x1080 59.94 Prores, live out in the field. So I take the uncompressed signal from my cameras HD-SDI out and record it directly into the compressed codec Apple Prores, through the MXO2. I also record AVCHD inside the camera as a back-up.


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    Frank Black
    Re: Is a capture and playback device a passthrough or a pitstop?
    on Dec 28, 2011 at 2:07:05 am

    Gary and David,

    Please excuse how long it took me to respond. Really, so sorry. Things just worked out this way... You guys really brought it down to my level. I appreciate your time. I posted in more than one cow forum and people really came through. I understand uncompressed now. I really was going in circles for about three weeks. Thanks a lot for your long answers. I actually have a clear picture if uncompressed now. You really helped me out. And I was able to pick up little tips and tricks from everyone who responded and was able to put together a REALLY clear picture of uncompressed. Thanks a lot, really. Best, Val


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    Frank Black
    Re: Is a capture and playback device a passthrough or a pitstop?
    on Dec 28, 2011 at 2:18:25 am

    I actually gotta say guys, your responses were from the ones that really spoke to me. You really put in the time and also the effort to bring it down CLEARLY to my level. I'm very happy to know uncompressed now. Thanks a lot.


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    Frank Black
    Re: Is a capture and playback device a passthrough or a pitstop?
    on Dec 28, 2011 at 3:31:47 am

    Guys, can you please help me further? I'm still researching I/O devices and am finding only definitions for many details.

    I'm trying to find about 3G-SDI/HDMI, 4:4:4 RGB, and conversions (and genlock if possible).

    So what if I have SDI? Tougher cables, etc... But so what? What stands out? Can it transfer better quality? Is that even possible?

    (beat)

    What is 4:4:4 RGB?


    And if I'm converting between 4:4:4 and 4:2:2 to set up single-link HD-SDI output, why am I doing this? And how is it happening?


    In up/down/cross conversions, do I choose one of the three (is there a button?). Can I choose NOT to choose one and to just let the data through? And how is it down? What happens to the footage? Do lines get added? And why would I need to do this? I know that in a broadcast setting, and I’m sure other settings as well, one may be given some SD footage and some HD and will need to kinda match them up. But why else?


    I'm sorry for cross-posting, but its very helpful, and I really need the help at the moment, and I take solace in the fact that as rude as it is, it doesn't hurt anyone as I'll take EVERY answer seriously. If you can help again, the way you did before, you would be doing a lot for me. Thanks either way.


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    Frank Black
    Re: Is a capture and playback device a passthrough or a pitstop?
    on Dec 29, 2011 at 2:47:57 am

    Hi David,
    I hope I'm not misunderstood by thanking everyone again, but I'm going back over what you guys wrote and just wanna say thanks again for certain details --

    this one is a real gem: The compressed file from a camera is hard(er) for an NLE to work with, that's why you capture to a different codec that is better for editing. Also this is why the "editing codec" is a larger file than the "recording codec", because the editing codec is less compressed.

    And the last paragraph is very helpful too. And the WHOLE thing is helpful as regards "uncompressed."


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