XDCAM EX vs. HDV

[rc444]

Hi there,

what's the main difference between XDCAM EX and HDV?

They both seem pretty similar (both formats are 4:2:0), the only differences to me is that XDCAM of course has 2/3 inch lens, and a bitrate of 35Mbps, compared to 25Mbps and 1/3 inch lens with HDV.

Also, which format do you think would is superior out of these three -- DVCPRO HD, XDCAM EX or HDV? DVCPRO HD would probably be superior being 4:2:2, but I could be wrong.

Thanks,
rc444

[Barry_Green]

You've asked a question that's a lot harder to answer than you know.

XDCAM is not just XDCAM. There's XDCAM-HD, in three different flavors, and then there's XDCAM-EX, in two flavors in 1080, plus XDCAM-EX in 720. So there's lots of different versions.

What they all have in common is that they're all long-GOP, interframe 4:2:0 MPEG-2.

XDCAM HD, in all three modes (18, 25, and 35 megabits) and XDCAM-EX in 25-megabit modes, all record at 1440x1080. XDCAM-EX in HQ mode records at 1920x1080.

XDCAM HD and XDCAM-EX in 25 megabits is basically the same as HDV, except the audio is uncompressed in XDCAM vs. compressed in HDV. Other than that, they're the same.

In 25 megabit mode, all versions of XDCAM HD and XDCAM EX and HDV record in constant bitrate. In 18-megabit and 35-megabit XDCAM HD, and in 35-megabit XDCAM-EX, it uses variable bitrate.

XDCAM EX uses two channels of uncompressed audio; I believe XDCAM HD uses four channels. This is significant, because it means that of the extra 10 megabits that XDCAM-HD gets over HDV, about half of that is spent on audio. And XDCAM EX has to cram 33% more video data into the same bandwidth, but its job is eased by losing two audio channels, which frees up 3 megabits. XDCAM EX will still be more compressed than XDCAM HD 35 megabits, but not by a whole lot, and it will have more spatial resolution data.

Which format is "better" or "superior"? Again, that's a loaded question, because people seem to have an awfully hard time separating the format from the camcorder. Formats are not camcorders. Yes an HVX is a DVCPRO-HD camcorder, but so is a $48,000 HPX3000. So you have to look at the format separately.

As a format, and as only comparing formats, DVCPRO-HD decimates HDV and is always superior to XDCAM-HD. The question arises with XDCAM-EX because EX records the full raster. Even so, it's 4:2:2 vs. 4:2:0, and long-GOP vs. Intraframe. In that comparison I would always choose the intraframe codec.

Let's put it a different way, which is a lot simpler to understand: DVCPRO-HD is Panasonic's answer to HDCAM. Both formats are directly comparable. Sony ranks its HD offerings like this: HDV is at the bottom, HDCAM is at the top, and XDCAM-HD is in the middle. So by that reckoning, and assuming that you agree that DVCPRO-HD is basically equivalent to HDCAM, then Sony would be saying that DVCPRO-HD is superior to XDCAM-HD.

We don't know how they'll position XDCAM-EX, but given that it's still a 4:2:0 format and still long-GOP I'm comfortable lumping it in with XDCAM-HD, but perhaps slightly above the existing XDCAM-HD.

But why does this all not matter? Because the camera head is usually more important than all this format stuff anyway. If you put a $5,000 HVX200 up against a $35,000 XDCAM-HD camera, guess what -- the XDCAM is probably going to produce superior-looking footage, even though the HVX has the better format! (I say probably because, again, it depends on the type of footage you're going for; people at WETA Digital did exactly this comparison for chroma keying, and ended up choosing the HVX as the product that delivered the superior key even against the $35,000 XDCAM 350).

Conversely, if you put a $48,000 DVCPRO-HD HPX3000 up against a $7500 XDCAM EX system, the HPX3000 is likely going to mop the floor up with the XDCAM camera.

But if you took that same comparison, and took off the HPX3000's lens and substituted in a crappy cheap lens, then the tables might turn again.

So you have to look at it all in overall context, as a complete end-to-end imaging system.

As formats go, AVC-Intra/D5/HDCAM-SR > DVCPRO-HD/HDCAM > XDCAM-EX > XDCAM-HD > AVC-HD > HDV. (and I suspect that 24-megabit AVC-HD will hold up very well to XDCAM-HD, but since there are no high-quality AVC-HD heads out there that's a test that'll have to wait a while.)

But unless you're buying a mastering tape deck, you're not buying a format, right? You're buying a whole system. So other things come into play, such as NLE support, ease of editing and post workflow, camera heads, lenses, etc. In that comparison, many of the top formats (like HDCAM) sink to the bottom because you can't edit HDCAM in its native codec on any NLE (except the Sony XPri, I believe). And XDCAM-EX isn't yet supported by NLEs, and neither is AVC-Intra, and very few editors support AVC-HD yet. Whereas most every editor has native DVCPRO-HD and HDV support.

Again, you have to look at the total system.

[mikkowilson]

Barry; Whats your source for 25mbps XDCAM-EX?

I was under the impression that XDCAM-EX was 35mbps only. That the 25mbps mode on the EX1 is simply traditional HDV(25) recorded to solid state.

I know that the HDV output connector is only active in 25mbps mode, and that it can't output HDV (or anything) when in 35mbps mode.

- Mikko

[Barry_Green]

Could be wrong; it was my understanding that XDCAM's 25mbps mode is bitstream identical in video, but that it uses uncompressed audio, and hence it is not technically HDV. And I further understood that XDCAM-EX continues that same format (although perhaps in an MP4 wrapper). But again, I could be wrong.

What it streams out the firewire port would definitely be compressed audio though, to make it HDV-compliant.

[mikkowilson]

We shall have to wait and see I guess.

- Mikko

[moldcad]

Could be wrong; it was my understanding that XDCAM's 25mbps mode is bitstream identical in video, but that it uses uncompressed audio, and hence it is not technically HDV. And I further understood that XDCAM-EX continues that same format (although perhaps in an MP4 wrapper). But again, I could be wrong.

What it streams out the firewire port would definitely be compressed audio though, to make it HDV-compliant.

So, I'm still uncertain on whether at 25Mbps, the EX1 will be 100% compatible with the HVR-DR60 disk drive, which can (only, I guess) record fully HDV-compliant, m2t files. This is of paramout importance to me, as I'm going to upgrade from the V1 and alredy have the DR60 drive. I was hoping that for as long as the SxS cards are so expensive, I could only record the 35Mbps stuff to them but should I need longer recording time, use the DR60 instead to get HDV...

[mikkowilson]

moldcad; I was told at IBC that yes the DR60 (and all other HDV decks/recorders) will work with EX1 in "SQ" (25mbps) mode.

- Mikko

[arges03]

Great info on the XDCAM/XDCAM-EX Barry! Lots of us are interested, especially with recent the hype around the EX-1. Thanks for breaking down some of the info related to the formats.

[moldcad]

moldcad; I was told at IBC that yes the DR60 (and all other HDV decks/recorders) will work with EX1 in "SQ" (25mbps) mode.

- Mikko
Mikko, thanks - yes I've heard that, but does the EX1 handle the DR60 in the "synchro" mode like the V1 does? Does it have anything in the menu/status screens for that purpose? And, last but not least, can I record to the DR60 without an SxS card?

[mikkowilson]

Those specific details I don't have, sorry. :(

- Mikko

[Simon Wyndham]

This is significant, because it means that of the extra 10 megabits that XDCAM-HD gets over HDV, about half of that is spent on audio.

Wrong. The 35M/bits/sec figure is for the video only. The audio is on top of that.

[Barry_Green]

That was the question -- so you're saying that the file size on an XDCAM-HD disc can theoretically go to 41 megabits (35 video, six audio)? I thought the write speed of the blu-ray disc used in XD-HD was only 36 megabits?

[Tim Le]

I thought the write speed of the blu-ray disc used in XD-HD was only 36 megabits?

The write speed of Professional Disc is capable of at least 50 Mbps since SD XDCAM was capable of 50 Mbps MPEG-IMX and the new MPEG HD422 can do 50 Mbps.

I think Simon is probably right. Sony says that a 23.3 GB single layer PD holds about 60 min of 35 Mbps HD video. So if we take 23.3 GB ( 23,300,000,000 bytes like the way storage is advertised) and convert that to bits, it's 186,400,000,000 bits. Divide that by the time (60 min = 3600 sec) and we get a bitrate of 51.7 Mbps. This is the theoretical, constant bit rate needed to fill up a 23.3 GB disc in 60 mins. Taken another way, if the 35 Mbps bitrate was the limit for both video and audio, it would fill up 15.8 GB in 60 mins, which is far below the capacity of the disc.

So it seems to make sense that the 35 Mbps of XDCAM-HD is only for video, especially since that bitrate is also VBR....unless my math is wrong :huh:

[Simon Wyndham]

Tim is correct. The max allowable data rate for video is around 50Mbps. The actual write speed is higher than this figure though because of overheads for proxy file creation and audio.

The drive units in the new 335 and 355 cameras are just shy of being twice as fast (120Mbps read speed compared to the current 70-75Mbps).

[TimurCivan]

interesting. Very interesting. I am very excited by this new camera.

[Elton]

I'm also VERY interested in this camera. The specs are phenomenal but it'll be interesting to see if it lives up to the CineAlta badge once it's out in the wild and getting a good shakedown. (hopefully without too much rolling shutter ;-) )

[dchai]

Played around with this baby, the lens is excellent, the matrix settings are very very customizable and the Sony rep says that the ISO is equivalent of ASA 800. I pointed around and am extremely impressed with the low light performance, low noise and clean image. Not noisy at all like the Panasonic HVX200 and even HPX500. This camera is going to sell like hot cakes. The resolution is clearly there, the CMOS has a more pleasing skin tone to my eye than even the higher priced XDCAM cameras.

Very exciting indeed.
David :D