HMC150 AVCHD VS Canon SLR MP4

H

Hunter Starnes

Active member
Hey guys,

I am wondering how the avchd codec in the hmc150 compares with Canon's 5D mkII, 7D etc. Can someone tell me which one is better and why?

Thanks,

Hunter
 
well avc is good ,but the canons record at a higher bitrate so the image is a bit cleaner ,im sure someone else can chime in with a summary of the pros/cons
 
According to de facto Panasonic spokesman Barry Green, shockingly, AVCCam is significantly superior to the Canon 7D format.

Now, we don't want to confuse this with a comparison of the 7D (or any current VDSLR) with the HMC150 (or other AVCCAM) in terms of cameras -- because any current VDSLR has all sorts of problems. BUT -- comparing the recording codecs -- is interesting.

Both codecs are MPEG-4/H.264. AVCCAM maxes out at 24 Mbps, in accordance with their global conspiracy agreement with Sony regarding the replacement format for HDV. For the 7D I've read both 44 and 48 Mbps.

So, the question is -- how is a 21-24 Mbps mpeg-4/h.264 stream better than a 44 or 48 Mbps mpeg-4/h.264 stream?

Fear not -- I'm sure Mr. Barry Green has a great answer.

Now -- for the record -- this is not some HMC150 or AVCCAM bashing question -- because the truth is that you really need to know what you're doing for 7D footage to not suck. I've been using the 7D next to the HMC150 and HPX170 for several months -- and I can honestly report that the 7D doesn't replace dedicated video cameras -- and especially not global shutter CCD cameras. But, the narrow focus of things the 7D does well -- it does extremely well.

All that being said -- I'm having a tough time trying to convince myself that the AVCCAM mpeg-4/h.264 codec (21-24 Mbps) is superior to the mpeg-4/h.264 7D codec (44 or 48 Mbps).
 
heres a simple translation from a lay man

avccam uses b frames in its encodings that helps in efficiently encoding the video and it is quite robust.
the canon does not have this and has to boost the bitrate to achieve a mudless video

lets say HYPOTHETICALLY they have equal image quality. (i cant say as there have been no test, however it is assured avccam produces superb quality better than hdv or xdcam)

both have equal image quality but the avccam only requires 24mbps while the other needs 45mbps.
 
Yes, it is because the AVCCAM AVCHD implementation uses bidirectional B-frames. AVCHD as implemented in the HMC150 uses a full IBP structure, instead of the DSLR's IP structure. So the GoP structure in the HMC150 looks something like IBBBPBBBPBBBP, whereas the GoP in the DSLR is more like IPPPPPPPPPPPPP. "B" frames are FAR more efficient to encode than P frames.

As such, the 21-megabits of PH mode in the AVCCAM products is a much more efficient, more robust, and overall better recording than the 50 megabits of IPPPPPPPPPPPP as found in the DSLRs. And does so in less than half the space.
 
i can't totally remember the terms, but i remember reading that one of the reasons avchd was so efficient is that it is constantly adjusting on the fly and deciding how efficient it needs to be. this is why it takes more cpu power to playback.
also, that there's something about the block size...avchd can use different block sizes....some parts of the image are more compressed than others, which, visually, can result in a better looking image with smaller file sizes. whereas, with a fixed block size, the entire image has the same level of compression...making it more susceptible to mud, requiring a higher bitrate to compensate.

i know that was a horrible attempt at an explanation, but i think there's some good info on it on the Panny site somewhere...
 
their both the same codec except the avccam has the b frame feature which reduces error in predicting frames.

It is possible that in the coming future that these dslrs would be able to record with b-frames.. for now they dont have the processing power to do this on the fly
 
Barry_Green said:
Yes, it is because the AVCCAM AVCHD implementation uses bidirectional B-frames. AVCHD as implemented in the HMC150 uses a full IBP structure, instead of the DSLR's IP structure. So the GoP structure in the HMC150 looks something like IBBBPBBBPBBBP, whereas the GoP in the DSLR is more like IPPPPPPPPPPPPP. "B" frames are FAR more efficient to encode than P frames.

As such, the 21-megabits of PH mode in the AVCCAM products is a much more efficient, more robust, and overall better recording than the 50 megabits of IPPPPPPPPPPPP as found in the DSLRs. And does so in less than half the space.
Click to expand...


So speaking of B frames in regards to the panasonic GH1 and GH2, from what I understand the GH1 did not use B frames, and the GH2 does. Now the GH2 can only record 720/60p at 17mbits. Will the image look cleaner with the B frame method even thought it's a lower bitrate/ the same as the GH1 bitrate?
 
The GH1 was limited to 17mbps in 720/60p mode. The GH2 has the same 17mbps, but with B-frames. It should look substantially better than the GH1.
 
Barry_Green said:
The GH1 was limited to 17mbps in 720/60p mode. The GH2 has the same 17mbps, but with B-frames. It should look substantially better than the GH1.
Click to expand...

Thanks Barry! I've been looking, but I can'at seem to find a good video comparing the I and P method, and then with B frames. Is there anything out there like this?
 
Not directly, that I can think of... the AVCCAM products do IBP in 17mbps, and the GH1 does 17mbps in IP, so you could almost compare them, except that they don't do the same modes. The AVCCAMs only do 17mbps in 1080/60i, and the GH1 doesn't do 1080/60i. The GH2 does 1080/60i, but it has IBP.

I guess the closest you could do is compare the GH2's 720/60p against the GH1's, that's probably 720/60 to 720/60, 17 to 17, IP to IBP.
 
Barry_Green said:
Yes, it is because the AVCCAM AVCHD implementation uses bidirectional B-frames. AVCHD as implemented in the HMC150 uses a full IBP structure, instead of the DSLR's IP structure. So the GoP structure in the HMC150 looks something like IBBBPBBBPBBBP, whereas the GoP in the DSLR is more like IPPPPPPPPPPPPP. "B" frames are FAR more efficient to encode than P frames.

As such, the 21-megabits of PH mode in the AVCCAM products is a much more efficient, more robust, and overall better recording than the 50 megabits of IPPPPPPPPPPPP as found in the DSLRs. And does so in less than half the space.
Click to expand...

Fantastic explanation...thanks Barry! I know I'm late in the game on this topic, but with the new Sony FS100 coming soon...I'm glad I found it. I'm a regular 5d user and am always frustrated that I cannot grade the footage too much as the codec seems to fall apart. If I shoot with a flat profile...when I add contrast back into the picture it makes for some serious noise and enhances the artifacts.

I am planning to get the FS100, but I'm wondering...can it's codec hold up considerably better than the 5d's codec in color grading?
 
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