XDCAM EX vs. AVCHD

[Chris7]

Wondering about the difference in quality between AVCHD and XDCAM (XDCAM EX and HD). So far as I can tell, both are interframe, long GOP, VBR, 4:2:0 codecs. AVCHD is MPEG-4 (H.264) and XDCAM is MPEG-2.

I have heard/read that MPEG-4 provides equal quality as MPEG-2 at half the bitrate (e.g. MPEG-4 recorded at 21 mb/sec should provide roughly equal quality as MPEG-2 at 42 mb/sec).

From these specs, it appears that AVCHD recorded at 21 mb/sec VBR should provide roughly equal quality as XDCAM EX/HD does at 35 mb/sec VBR.

From what I’ve seen from consumer cameras, AVCHD is inferior in quality to even HDV, but I’ve heard this is likely due to the conversion chip in these cameras. And I don’t think the AVCHD Panisonic HMC-150 has a direct comparison (I don’t think the XDCAM EX JVC100U really counts).

Does XDCAM EX/HD provide superior quality to AVCHD, provided that the a proper in-camera conversion chip is used?

Why is AVCHD considered a “consumer” format, while XDCAM EX/HD is considered “professional.”

I realize that AVCHD is much more difficult to work with in post (more taxing on the CPU if edited natively, and requires a generation loss if converted into ProRes for editing, for example). And also, AVCHD was originally introduced to consumer cameras, while XDCAM EX/HD was prosumer plus from the beginning. Other than that it seems like they should be of the same quality, and so should be considered pretty much equal (at least in theory, based on the specs).

(BTW, I do not understand the difference between XDCAM EX and XDCAM HD, but I believe they are both long GOP 4:2:0 codecs in MPEG-2 VBR 35 mb/sec. What’s the difference?)

 

[cpcarrot]

The main flaw in your assumption is simply:

“I have heard/read that MPEG-4 provides equal quality as MPEG-2 at half the bitrate (e.g. MPEG-4 recorded at 21 mb/sec should provide roughly equal quality as MPEG-2 at 42 mb/sec).”

As that is just simply not true. The main advantage XDCAM EX has over AVCHD is it’s improved bitrate which does equate to a better quality image. Would be great if MPEG-4 really could give you twice the quality for the same bitrate but it doesn’t come close to that.

 

[Chris7]

Clarification

The main flaw in your assumption is simply:

“I have heard/read that MPEG-4 provides equal quality as MPEG-2 at half the bitrate (e.g. MPEG-4 recorded at 21 mb/sec should provide roughly equal quality as MPEG-2 at 42 mb/sec).”

As that is just simply not true. The main advantage XDCAM EX has over AVCHD is it’s improved bitrate which does equate to a better quality image. Would be great if MPEG-4 really could give you twice the quality for the same bitrate but it doesn’t come close to that.

Not wanting to debate here -- there's tons of pro's on this forum that know a thousand times more about this stuff than I.

But I want to be clear that I am not saying that "MPEG-4 gives twice the quality [as MPEG-2] for the same bitrate." How much better AVCHD looks than MPEG-2 at a given bitrate is the subject of some debate, but I've never read that it's anywhere near "twice the quality."

What I have read is only that MPEG-4 provides equal quality as MPEG-2 at half the bitrate. (A google search for "H.264" "MPEG-2" "bitrate" and "half" yields a lot of results.)

So this info is inaccurate?

Thanks,
Chris

 

[MisterMe]

...
So this info is inaccurate?

...

The premise of your OP is flawed in many fundamental ways. XDCAM EX is the third generation of the XDCAM tapeless professional video system. You want to know how it compares to a AVCHD, a tapeless format for consumer videography. How do they compare? They don't.

 

[filman408]

What about XDCAM EX versus DVCPRO HD? They are both "pro" codecs.
Like in the Sony EX1/3 or the Panasonic 170...

 

[LethalWolfe]

The premise of your OP is flawed in many fundamental ways. XDCAM EX is the third generation of the XDCAM tapeless professional video system. You want to know how it compares to a AVCHD, a tapeless format for consumer videography. How do they compare? They don't.

I for one would like to hear all the ways Chris7's premise is fundamentally flawed. The OP is asking a question so I fail to see how he can have a flawed premise when he has presented no premise but merely asked for clarification.

The biggest reason, IMO, XDCAM EX/HD is considered 'pro' and 'AVCHD' is considered 'consumer' is because XDCAM is marketed as a 'pro' solution and AVCHD is marketed as a 'consumer' solution. AVCHD will be allowed to get to close-but-not-quite in terms of quality and usability as long as Sony and Panasonic have higher quality codecs 'reserved' for the pro market (again, IMO). I think the wild card is Nikon and what it does along the vDSLR route as Canon will hamper it's vDSLRs as long as possible until it figures out what to do w/it's camcorder division. Red is obviously going to stick to there own RedCode compression scheme so they don't have a horse in this race.

Some differences between XDCAM EX and XDCAM HD are that HDCAM EX is full raster and capable of 1080i/p and 720p modes. XDCAM HD, IIRC, is 1080i60 only and not full raster (it's 1440x1080). There is a new XDCAM HD format that is full raster, 50Mbit/s, and 4:2:2.


Lethal

 

[TheStrudel]

AVCHD is limited in a few ways. For one, it is chroma subsampled to 4:2:0. (So is HDV. XDCAM EX is capable of 4:2:2, though isn't implemented in recording) For another, the AVCHD you see in consumer cameras is both limited by the hardware at hand (CMOS chips, lenses), and it's less sophisticated than the AVC-Intra compression being used on newer, more expensive Panasonic cameras (among others). I suppose that the format can be used at a higher level - and is - but not in slower media such as SD cards. That said, it's not always employed at the highest bitrate either, often giving HDV an edge there as well. I think most of the newer formats are AVC derivatives, but AVCHD is one of the more basic implementations.

 

[LethalWolfe]

AVCHD is limited in a few ways. For one, it is chroma subsampled to 4:2:0. (So is HDV. XDCAM EX allows 4:2:2) For another, the AVCHD you see in consumer cameras is both limited by the hardware at hand (CMOS chips, lenses), and it's less sophisticated than the AVC-Intra compression being used on newer, more expensive Panasonic cameras (among others). I suppose that the format can be used at a higher level - and is - but not in slower media such as SD cards. That said, it's not always employed at the highest bitrate either, often giving HDV an edge there as well. I think most of the newer formats are AVC derivatives, but AVCHD is one of the more basic implementations.

The EX camera hardware operates in 4:2:2 (so it can send a 4:2:2 signal out via HD-SDI, for example) but the XDCAM EX codec itself is 4:2:0.


Lethal

 

[knello]

It's simple, really: XDCAM EX is HDV with an extra 10Mbps, which gets recorded to a disk instead of tape.

If you don't like the 4:2:0 limitation, you can get around that with an HD-SDI tether.