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Mysterious stuttering in Mini Recorder captures

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Jeff Mann
Mysterious stuttering in Mini Recorder captures
on May 14, 2014 at 11:14:42 pm

Hi, I'm having a problem with intermittent "stuttering" in parts of some Prores 1080p footage captured with our Blackmagic equipment. This was the first shoot we've done with it. I'm having a hard time diagnosing the cause of the problem, maybe someone recognizes it?

There's a short example of the problem here:

During playback, the stuttering always happens in roughly the same part of the footage, but not always on the same frames. Also, it doesn't happen every time. If I set the above clip to play in a loop in QuickTime Player, sometimes it plays perfectly smoothly, and sometimes with very noticeable stuttering. I've played it on several different computers, all of which should have no problem playing back a normal Prores HD file, but they all do the same thing. I tried converting it to uncompressed, and playing it from a RAM disk. The CPU runs less than 40%, but I still get the same thing, sometimes playing smoothly, sometimes stuttering around the same place. Also tried transcoding to 720p H.264, again the same. If I step through it frame by frame, everything looks fine. Is there some kind of utility that one can use to inspect the frames and structure of a video file, to see where the problem might be?

We can't do the shoot over again, so I'm really hoping there's some way to make it play back consistently.

The footage is 1080p/29.97 Prores 422 captured with Media Express 3.2.4. It was captured from a Sony EVIHD1 camera, going SDI through an ATEM 1ME Production Studio 4k, into a Decklink Mini Recorder, in a Mac Pro 4,1 8-core 2.26GHz, onto an internal drive with 180MB/s read/write. There were no dropped frames reported during capture. I also captured from a second EVI camera, through the switcher, to a MacBook Pro with OS X 10.8.5 and Ultrastudio Thunderbolt Mini Recorder, onto a >65MB/s Firewire 800 drive. Both captures are giving problems with stuttering in certain parts of the footage.

Any advice appreciated, thanks.

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