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View Full Version : AVCHD implementation in the GH1.



Skeptikal
07-20-2010, 05:30 PM
I had a Canon 5D2 for a year, but I'm a total beginner with the GH1. I recently read something on Phillip Bloom's blog (discussion of the new Sony NEX VG10) that I find curious:



"Sony’s 24Mbit is decent – fine – no problem. The hacked GH1 needed 44Mbit AVCHD because it had such a dodgy implementation of AVCHD with tons of bugs, like a spike in P frames causing ‘mud’ and a complete break up of the image on occasion."

I thought AVCHD was a standard that manufacturers had to abide by and the main limitation of it in the GH1 was the low 17 mbps rate. However, the person who wrote this (he also has his own blog about the GH1) seem to be implying that a "well implemented" AVCHD @ 24 mbps could be as good as a "dodgy implementation" @ 44 mbps.

I'd appreciate any comments on this from experienced GH1 users.

Barry_Green
07-20-2010, 05:38 PM
The AVCHD implementation in the GH1 is indeed quite weak and cannot hold a candle to the 21mbps of AVCHD in the AVCCAM products. Panasonic appears to have punted on the codec on the stock GH1.

The camera is capable of really rather remarkable results, if the codec is given enough bandwidth, and that's what the PTool allows you to do.

A well-implemented, proper fully-realized codec like AVCCAM's PH mode (utilizing I, B, and P frames) would probably substantially outperform even the 44mbps of the GH1's modified codec.

Skeptikal
07-20-2010, 05:48 PM
That's interesting...and I always thought the camera makers had to implement AVCHD according to some rock-solid guidelines.

I guess Sony's NXCAM is comparable to Panasonic's AVCCAM. It's interesting that they both max out at 24 mbps.

Would it be reasonable to assume that the new consumer camcorders like the JVC GZ-HM1 with AVCHD @ 24 mbps are also using an efficient AVCCAM type codec?

Thanks Barry

Barry_Green
07-20-2010, 09:32 PM
They both max out at 24mbps, because the AVCHD specification calls for a maximum data rate of 24mbps.

I would certainly expect Sony's NXCAM to be operating comparably to Panasonic's AVCCAM; if it isn't, that'd be a huge fail on their part. But seeing as they are co-sponsors and co-inventors of AVCHD, I can't think of any reason why NXCAM would be anything other than top notch and comparable to AVCCAM. Only problem I've heard of with it is some sort of audio issue that makes it incompatible with Apple's NLE right off the bat, but presumably that's either already been fixed or will shortly.

As for JVC... I have no idea. Frankly I was startled when the GH1's AVCHD turned out to be so sub-par; I thought the badge of AVCHD would mean a certain standard, but apparently it doesn't imply any minimum level of quality. So while in normal circumstances I would expect any version of AVCHD to be of full quality, in practice it means that we can't really take anything for granted. Still, I would be quite surprised if it was a stripped-down version.