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Full Frame Rate Broadcast Recording with Wirecast

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Brian Alexander
Full Frame Rate Broadcast Recording with Wirecast
on Feb 19, 2014 at 11:30:19 pm

Anyone have any luck achieving a full frame-rate recording with Wirecast? I'm looking to help some colleagues solve some issues in this area and thought I'd come here first. Sure, I can peruse the manual but some of you (Craig) have been answering questions for years and may be able to pinpoint my exact needs without effort. I, in the meantime, will be perusing the manual.

I'm familiar with the correlation between bit-rates, codecs, processors, HDD/SSD speeds, etc. so at least we're not starting from scratch when answering my questions.

First, a little bit about what I'm doing with Wirecast:
Very little. I am treating Wirecast as a recording interface rather than a production switcher.

High Frame Rate Recording:
What is the best configuration for getting the highest frame-rate H.264 encoding? (without Matrox Max)
Turn off PVW screen?
Lower frame rate of playback within my PVW windows?
It appears that I can take advantage of the Matrox Max chip on the capture card by doing an ISO recording but that doesn't work for all of the techs I know.

Audio Drift:
I've heard of audio drifting reports. Not a standard delay which would be easy to fix in post (or pre for that matter) but fluctuating delay times throughout the file.

This screams of mismatched sample rates between the source sample rate and recording settings. What are your thoughts?

I appreciate any pointers you can provide. I want to see Wirecast succeed!!


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Craig Seeman
Re: Full Frame Rate Broadcast Recording with Wirecast
on Feb 19, 2014 at 11:59:32 pm

Wirecast 5.0.1 and use x264 .mp4 to record to disk. Best to use external fast disk (7200rpm USB3 or Thunderbolt for example).

I'm not sure what you mean by audio drift. Audio tends to remain synced with my input sources.
Or do you mean recording?
Wirecast records a slightly variable frame rate to avoid dropping frames. The audio doesn't drift in a player but might if an NLE tries to lock it to a standard frame rate. FCPX, for example, seems to handle it well, For other NLEs you may want to transcode the recording to a locked frame rate.

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Brian Alexander
Re: Full Frame Rate Broadcast Recording with Wirecast
on Feb 20, 2014 at 1:09:49 am

Hi Craig,

Yea, the audio drift is related to the recording - audio is solid when viewing the 'live' source. It's the same type of drift found when inadvertently recording or transcoding a 44kHz source to 48kHz.

You bring up a good point about VFR encoding. I'm guessing the audio and video run through their respective encoders before being combined in their output container. If that's the case it would make sense that complex video scenes may drop the frame rate slightly while the audio encoder is sailing right along with no problem. This may cause the delay that is being reported.

Is the only way to take advantage of Matrox Max through the ISO recorder?
What is the difference between choosing the Matrox source under MATROX INPUT DEVICE vs. the Matrox source under the SYSTEM DEVICES in the Source Settings preferences?

Thanks for your help Craig.
Much appreciated.

Brian Alexander, ISF, ISF-C
Sr. Video Engineer

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