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Data Rate questions
I’ve got a few questions about data rates and storage options. I’ve been finding conflicting information about almost everything I’ve tried to look up so far.
I am watching animations made in After Effects with the DVCPro HD codec….in Final Cut via a Decklink HD Pro card.
I’ve been having lots of problems with motion jitter in some of the animation moves. I’ve worked through every other fix and tweak and the only thing I am left with is that my drive does not have a fast enough data rate to playback the animations.I’ve read in several places that DVCPro HD data rate is 100MB/sec. I’ve also seen a few places that state it is 15MB/sec.
This is quite a discrepancy! Which is correct?Blackmagic’s Speed Disk test tells me that my extra internal render drive is working at 48MB/sec. If DVCPro HD plays at 15MB/sec, then this drive speed is sufficient and I’ve got to figure out what else could be making my motion jumpy.
If DVCPro HD plays at 100MB/sec, then I need to find myself a faster storage solution ASAP.
I can’t spend a lot because I really only need the faster storage for HD and I will more than likely not have any other HD projects for at least a year. I’d hate to blow lots of money that I don’t have now…..to find it outdated by the next time I needed it!I was told that Medea’s G-Raid Firewire 800 storage is an affordable possibility. However, I am getting some mixed messages from their website.
It says it supports 3 real-time video streams of DVCPro HD, 4 of HDV and 7 of DV streams. The compatibility chart with Blackmagic does not mention HD capabilities at all though. The model info page says that the G-Raid has a max data rate of 75MB/sec.
How could it support 3 streams of DVCPro if it doesn’t even have a data rate of 100MB/sec?
I tried to get a Medea sales rep on the phone to discuss it, but couldn’t get anyone to call me back.I need to figure this out by tomorrow. I am supposed to output and deliver stuff by next week!
Can anyone speak with authority on any of these topics?Thanks!
alisa -
6 Replies
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Hi Alisa,
The confusion between the numbers people are telling you relates to bits (b) versus bytes (B). Remember that there are 8 bits to every 1 byte.
DVCPRO HD is often referred to as DV100. It has a data rate of 100 mega bits per second, ie 100 Mb/s. If you divide this number by 8, in order to express it as mega bytes, it will return 12.5 mega bytes per second, ie 12.5 MB/s. We quote 14.5 MB/s in our documentation so as to include both audio and video date.
The DVCPRO HD data rate should be expressed as 100 Mb/s and not 100 MB/s. As with other DV formats, it’s data rate is fixed, regardless of whether you are using HD 720p or HD 1080 formats, and regardless of the frame rate.
I am quite sure that a FireWire 800 solution will be fine for this purpose because even my 3G iPod can handle capture and playback of HDTV1080 video in the DVCPRO HD format and iPod’s use energy-efficient disks which are comparitively low speed.
Can you provide some sample clips for us to review and also tell us from what source they were created? Hopefully we’ll be able to diagnose what is going wrong.
Regards,
Luke Maslen
Blackmagic Design -
Thanks so much, Luke.
I put an example up on my server. It can be accessed at:
https://webftp.powweb.com/?action=logout
hostname: terra.powweb.com
username: alisagraphics
password: graphicsThere is a DVCPro HD animation on there that is giving me the ‘motion jitter’ problem during the move. I also included the folder with the After Effects project in it that I used to make the animation.
So, if DVCPro HD only has a 14MB/sec data rate, then my maxtor render drive with a 48MB/sec data rate shouldn’t have a problem playing it back, right?
Or is there something very different just in the striping process that would make the Medea Firewire 800 solution work much better?If it IS in playback, I need to fix it today by ordering different storage solutions.
If it isn’t in playback due to data rate, I’ve got to figure out what I’m doing wrong in the project file.
However, after an extremely long process-of-elimination period of tests……It seems to me that it must be a playback issue.
My main problem is that there is NO ONE that I know in Boston with an HD setup that I can go test with. I’m going to overnight an example to the online editor in Canada to check on his system.
But, I am actually supposed to be outputting all of the finals this weekend. ……stress……Best,
Alisa -
Hey alisa. I downloaded and watched your move on the map. I see no image stutter. What I did notice is that the audio is rendered out at 44.1 which might be choking FCP. EIther mixdown/render the audio or rerender the audio out at 48khz. You should also turn on the dropframe alert to see if in fact FCP is dropping frames. If it is turned off and FCP is dropping frames, then the image will appear to stutter. You can find it in the user preferences>General tab & make sure the ‘report dropped frames during playback’ is checked.
Let me know how that works out.
Your drives should be able to process the DVCPro HD material by the way.
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Thanks, Jeremy.
I really appreciate you taking the time to check it out.
Best,
Alisa -
Hi Jeremy,
That’s great info. While I’m waiting for the files to download, another thing Alisa can check is the RT popup menu at the top-left of her timeline. I suspect that the RT playback quality is set to High and this will cause problems if RT effects are applied. Reducing Playback Video Quality it to at least Medium should help overcome any jittery playback if this is a factor.
You are absolutely correct that the audio needs to be 48kHz as that is a TV standard and DeckLink cards always require 48kHz audio
Regards,
Luke Maslen
Blackmagic Design -
Luke,
Were you able to download and play that animation?
Did it have a motion jitter when you played it?I do have ‘report dropped frames’ selected in the settings and it hasn’t reported any dropped frames.
I’ve spoken to several people about the storage and data rate and now am led back to believe that is not my problem.
It is either something in After Effects (moving too many pixels, too quickly) or perhaps something in my video card. Not sure it could be the video card though because many animations look great. It is only the fast moving ones that are givng me a problem.Didn’t know that thing about the audio though. I only had audio on as a reference. These don’t have to have sound at all.
Is that something that could trip up Final Cut and the Decklink in this way?
Thanks for your time.Alisa
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