Desktop Video 9.7 causing H.264 Pro Recorder glitches

We've been happily using Blackmagic's H.264 Pro Recorders for over a year now with only a few hiccups. A couple of my crew had mentioned that a some captures were failing out in the field, so since I'd never updated Blackmagic's software (still using the version that came on the CD), I figured it's about time I do that.

Last week we updated 4 MacBook Pros (i7's, 8GM RAM, Late 2011 models) and all of them experienced the same issue capturing video through the Media Express software.

Our issue: About every 10-30 seconds or so, there would be 1/2 second or so of very bad digital pixelation that would appear around anything in motion on the video. It would resolve itself within a second normally, but obviously made the captured video unusable. The pixelation would never appear on the preview window of Media Express, only on the resulting saved mp4 file.

We're capturing directly from Canon XF305s, at 720P 59.94

Things we tried with zero effect:

• Switching the SDI cable from the camera with another one
• Changing the output from the camera to an HDMI cable
• Switching the H.264 Pro Recorder out with another one
• Switching the computer out with another one
• Switching the camera out with another one
• Switching out the USB cable out with another one
• Changing the bit rate which we were capturing (was the standard 5.5Mbps)
• Changing the capture setting from "Native: Progressive" to all of the other options

After scouring some forums, I found a few other older issues about this (including one with a sound off-sync issue which thankfully we've never experienced!), and someone mentioned using an older version of Blackmagic's software would resolve the problem.

I went back into Blackmagic's support site to download the software and looked under "Archived Drivers" where I grabbed 9.6.4 and reinstalled that. It seemed to lessen the issue, but didn't eradicate it until we switched to the setting "YouTube 720P". That seemed to get rid of the issue altogether.

ANY ideas of what's going on here?

looks like you've set the "quality" (or bit rate) too low.
Mpeg uses GOP (group of pictures) to encode, with one I frame, and plenty of P frames
the I frame, which encodes the entire picture, is constrained by the constant bit rate, thus you get a not so nice picture every X seconds (X depending on the length of the GOP)
it goes like this

Code: Select all

I P P P P P P P P P I P P P P P P
                      ^ nicer
  ^ nicer         ^ beautiful
^ crappy            ^crappy


Thank you Raphaël for the explanation of I and P frames, and that explanation makes sense for the kind of picture we were getting.

What's weird is that we've been capturing at bitrates from 3-5Mbps for over a solid year now with this exact camera setup, at multiple venues across the country, 2-3 times per week, and it was only when we updated the software that we experienced this glitch. I'm just wondering if anyone else experienced something similar with Desktop Video version 9.7, or if we're dealing with a gremlin here.

We experience a similar issue with our H.264 pro recorder. Our video path is a bit more complex, but we do have a XF305 amongst our sources, along with a Sony BRCZ330, and two generic 720p fixed cameras, all running at 720p 60fps (in pal). We definately lessened our glitching by changing the compression ratio. As we are mixing the video with the ATEM Software, the capture happens in the ATEM2 Software panel, we found that if we had the compression set to "23%" it records without any glitching, if we set it any higher we get the same glitch you are describing. The bitrate is around 5.5, not entirely sure how the % compares exactly with the bitrate, but certainly our results have been a lot better now that we dropped down, (we were recording at 26%, which glitched about once every 30-40 seconds).

Here is my original topic:
viewtopic.php?f=10&t=4214