Audio Sync issues in Hak5 409, the fun of HD on the hacker level
Posted on October 31st, 2008 | by admin |
You may have noticed an audio sync issue in Hak5 episode 409. This is all part of the “fun” that comes with the ordeal of is changing our production pipeline.
Prior to 408 we shot with yucky analog video and audio. With 408 we implemented the first part of our HD plan with the use of an HDMI matrix switcher and two Black Magic Intensity HDMI capture cards on a Mac Pro using the Black Magic On-Air mixing software.
It’s a really slick bit of kit the essentially does the work of $15k in hardware in half the price. But as always going the “hacker route” comes with, bugs shall we say.
The bug we’ve encountered is that the audio and video get out of sync, especially when fading between channels. This is why you’ve seen hard cuts between camera and PC video instead of a nice dissolve.
What we end up with is a video clip with audio slightly shorter than the video. In episode 408 I was able to pretty much fix this by stretching and moving the audio to match the video. When it came to edit episode 409 I thought I had figured out the sync trick by stretching and matching lips at the end of each clip. As it turns out I did in fact get the end of the clip to match, but the beginning became further off until slowly, things finally sync’d up at the end.
Getting the sync right is difficult, especially when editing on a PC using Sony Vegas because the codec we record in, DVCPRO HD, isn’t natively supported so I had to purchase a $100 third party codec and even then I’m only getting about 4fps in preview. Sure it’s only a dual core with 4 gigs of ram but I was hoping to get a bit better performance.
So anyway this isn’t a permanent solution. We’re aiming to be editing in HD with Final Cut Pro on a mac as soon as we can afford to.
As for the audio sync, we figure this was due to the inadequate system specs of Paul’s Mac Pro, which we’re borrowing for capture until we can buy our own. We have since added a RAID0 and tripled his RAM. Hopefully this will fix the audio sync issues with the next shoot. We’ll find out tonight or tomorrow as we do Hak5 episodes 411 and 412. If not we’ll have to have a conversation with the tech’s over at Black Magic Design because our entire HD production process hinges on their hardware working as expected.