35 Mbps average or maximum rate?

[Michael Mann]

35 Mbps VBR - does this number define average or maximum bit rate?

[Robert Schemitsch]

the maximum bitrate.
but don't try to compare XDCAM with the 25Mbit CBR of HDV.

[Michael Mann]

"but don't try to compare XDCAM with the 25Mbit CBR of HDV."

Why not ? Please explain.

If 35 VBR defines the maximum rate - does this mean that, depending on the content of the image, the AVERAGE bit rate of 35 VBR mode can drop significantly even below 25 Mbps?

[Herman Van Deventer]

Jackpot Question ! Michael -

Eager to see feedback on this one -

[Robert Schemitsch]

No, i'm sure it can't drop under 25Mbit.
The comparison between HDV and XDCAM is non-permissible because XDCAM uses a better codec. I tested my 350 under several conditions. I came to the following conclusion:

18Mbit XDCAM HD = 25Mbit HDV
25Mbit XDCAM HD compares to a fiktive HDV50
an the 35Mbit HD is nearly DVCPROHD.

Thats my opinion ;)

[Carlo Sigismondi]

Originally Posted by Robert Schemitsch

an the 35Mbit HD is nearly DVCPROHD.

Robert, have you seen some of the tiffs in xdcam ex forum? Clearly they're grabs from some blueray disc...But...have you seen some macroblocking artifacts in Xdcam 350 like those tiffs at 35mb ? In your experience at which datarate xdcam could show artifacts like those tiffs? thanks

[Steven Thomas]

Originally Posted by Carlo Sigismondi

Robert, have you seen some of the tiffs in xdcam ex forum? Clearly they're grabs from some blueray disc...But...have you seen some macroblocking artifacts in Xdcam 350 like those tiffs at 35mb ? In your experience at which datarate xdcam could show artifacts like those tiffs? thanks

I'm surprised there has been little discussion about those tiffs.
Some look good, and some look really bad.
Why the macroblocking if the codec is supposed to be better than HDV?

[Andy Mees]

Originally Posted by Michael Mann

"If 35 VBR defines the maximum rate - does this mean that, depending on the content of the image, the AVERAGE bit rate of 35 VBR mode can drop significantly even below 25 Mbps?

as far as I understand it Michael, yes it can drop below 25 Mbps.
you have to think of it in terms of the mathematics. where fast moving high detail images will need all 35 Mbs to encode the data, static low detail images will need significantly less, perhaps less than 25 Mbs (maybe even a lot less) ... but so what? what would be gained by storing redundant image data? the 25 Mbs CBR of HDV dictates that a full 25 Mbps of image data be retained even when that data is not needed, this is the down side to any CBR format, MPEG or otherwise.

[Robert Schemitsch]

mysterious ;).

Some month ago, i think, i read the specs fpr the XDCAM HD HQ - Mode, where it says max bitrate is 35, average is 30, and minimum is 25.
Yes, if i find some free time, i'll post a tiff of the 350 in HQ-Mode.

[Michael Mann]

Originally Posted by Andy Mees

... what would be gained by storing redundant image data? the 25 Mbs CBR of HDV dictates that a full 25 Mbps of image data be retained even when that data is not needed...

Andy, I thought for more static images there is not redundant data stored but a lower compression applied. And that might be visible. Isn't that so?

[Michael Mann]

Originally Posted by Robert Schemitsch

Yes, if i find some free time, i'll post a tiff of the 350 in HQ-Mode.

Please do, Robert.

[Michael Mann]

Originally Posted by Robert Schemitsch

The comparison between HDV and XDCAM is non-permissible because XDCAM uses a better codec.

Hhm ... I found this in the EX brochure:

"This highly efficient “MPEG-2 Long GOP” codec – that is also
adopted in the XDCAM HD and HDV 1080i series of
products – enables users to record stunning-quality HD
video and audio over a long period of time by efficiently
compressing the data."

That doesn't sound like a big difference in quality of codecs, does it?
Anyway, I'd be pleased to learn that the XDCAM codec looks better than HDV, Robert.

[Greg Boston]

Originally Posted by Michael Mann

Anyway, I'd be pleased to learn that the XDCAM codec looks better than HDV, Robert.

We already learned this in March 2006 when the XDCAM HD cameras were first released. The XDCAM EX expands on that already good looking image.

The 35mb VBR codec can go up or down as needed. I was even told by a Sony engineering type it can briefly spike a little higher than 35 mbs under certain scenarios.

The VBR is more efficient for storage capacity vs. quality. Large, static, unmoving, solid color objects can be compressed more without a loss of visual quality.

-gb-

[Steve Connor]

I haven't seen ANY macroblocking on any of the footage we have shot over the last year. XDCam HD code is very solid and VERY different to HDV.

You can't comment on .tiffs posted on the web you have to see original footage.

[Greg Boston]

Originally Posted by Steve Connor

I haven't seen ANY macroblocking on any of the footage we have shot over the last year. XDCam HD code is very solid and VERY different to HDV.

You can't comment on .tiffs posted on the web you have to see original footage.

Well stated, Steve. And very true!

My favorite XDCAM HD story is the one told about the big wigs evaluating XDCAM HD and viewing a freeze frame of a helicopter in flight. One of them tried to point out the macroblocking artifact on one of the main rotor blades.

Fortunately for all, an astute observer with aviation knowledge pointed out that what they were in fact seeing, was the trim tab on the rotor blade!

-gb-