HDV compared to HD

[Markinout]

I'm planning a project that will be creted as HD (1920 x1080) jpeg image sequences and posted in DS NItris. The delivery is in SD but I wish to archive high definition master to tape.
Does anybody know: is the spec of HDV high enough to be used in this way? Can anyone give me a direct technical comparison of the two formats (HDV & HD) regarding compression, image size etc?

[Alan Roberts]

Yes, I can give you all the info you need and a lot more.

HD image resolution comes in two flavours:

1920x1080 (at a variety of frame rates, and interlaced or psf (film-style)).
1280x720 (at the same variety of rates, but always progressive, often used to generate frame-duplicated film-look as well)

HDV image resolution also comes in two flavours:

1440x1080 (same rates as for HD, plus interlaced and psf).
1280x720 (as for HD)

But, HD is 4:2:2 chroma sampled while HDV is 4:2:0, that means you get only half the vertcial chroma resolution in HDV.

HD recording formats also have flavours:

HDCAM is only 1080. Luma resolution is 1440 and chroma is 480, expressed as 3:1:1. Compression is 4.3:1, intraframe (i.e. I-frame only), 144Mb/s.
DVCProHD100 has two variants:
720p. Luma resolution is 960 and chroma 480, expressed as 4:2:2. Compression is 6.7:1, intraframe with smaller blocks than HDCAM.
1080. Luma resolution is 1440 and chroma 720 in 50Hz versisons, 1280 and 640 in 60Hz versions, both espressed as 4:2:2. Compression is 6.7:1, intraframe.

At the higgest end of this game, there is also HDD5 recording (1920x1080 or 1280x720, both 4:2:2 at 3.5:1 compression, 350Mb/s), and HDCAM-SR which can do 1920x1080 at 4:2:2, 440Mb/s, and 1920x1080 at 4:4:4, 880Mb/s, both short-GoP MPEG4 at 2.7:1 compression).

I'd be wary of using JPEG for HD, unless you're using JPEG2000. It's more usual to go for something like MXF files when working at the top end of HD.

Hope that helps.

[Markinout]

Thats very good infomation Alan, thanks.

[Bruce]

Alan - could I ask if you have any views on the new DNxHD Avid codec for editing HD?

Is there a BBC promulgation on compressed HD post production?

Just contemplating going HD rather than HDV for a future project.

[Markinout]

I think Sky have adopted the avid DNxHD codec for their machines. they use DNxHD at 185Mb/s (10bit full raster) and this actually uses less storage than SD. They run Nitris on a Unity system. DNxHD is switchable between 120Mb/s or 185Mb/s on my Nitris here in Manchester.

[Alan Roberts]

I've no information on BBC practice these days, I've retired :)

But I can always ask.

[Unicorn]

Yeah, DNxHD-185 seems to work well. Certainly HDV->DNxHD->MPEG-2 is basically indistinguishable from the original footage.

[Bruce]

Have just looked at Avid Adrenalin today. Have been told that HDV has been cracked and is best put through the Avid HD codec.

Am now confused having read that 1080i it the preferred format - had thought of getting Sony 730s. But now should it be the 750 with 25p. HD is a minefield.

[Alan Roberts]

1080 is the preferred format for the UK. Interlace for sport, news etc, psf for drama and film-look. psf travels as though it were interlace, but is actually progressive, but only at 25fps, not the 50fps that 720 will run at.

The HDW750 will shoot 1080i/25 (i.e. interlaced at 25 frames/second, 50 fields/second) and at 1080psf/25 (i.e. progressive frames at 25/second, delivered as interlaced fields for transmission, just like film). The HDW730 sells in the US and is like the 750 but at 29.97 instead of 25. The HDW730s is the cheap version, shooting 1080/25 and 1080i/29.97, no progressive or psf (progressive with segmented frames). Pansonic Varicam is 720p only, tape runs at 59.94 or 60 frames/second, the camera runs anywhere between 4 and 60 fps, most use is for 25fps film look, with under/over cranking. HVX200 is like that but runs at fewer spot speeds.

And so on.

[Unicorn]

Have just looked at Avid Adrenalin today. Have been told that HDV has been cracked and is best put through the Avid HD codec.

Not sure about Adrenaline, but with Xpress Pro HD it's basically a trade-off between CPU and disk space. Native HDV uses less disk space than DNxHD but more CPU, so if you have lots of fast disks, then DNxHD would be a better way to edit: you won't see any significant quality drop from the original HDV footage, but it will handle realtime effects better since it only has to decompress the individual frames it's processing not multiple frames of MPEG-2.

[Bruce]

The Avid man was telling me that HDV is ok until you use effects of any kind. Once its not straight cuts the quality can diminish a graet deal. Looks as if Avid with their special codec or Canopus with HQ codec may be the solution.

[Unicorn]

The Avid man was telling me that HDV is ok until you use effects of any kind. Once its not straight cuts the quality can diminish a graet deal.

Sounds like they don't know their own software :). Xpress Pro HD renders HDV effects using the DNxHD-120 codec, which won't be quite as high quality as DNxHD-185, but still seems fine to me as a compromise between quality, performance and disk usage. I presume Adrenaline would be at least as good.

Again, though, if I had a fast RAID system with a few terabytes of disk space, I'd convert everything to DNxHD-185 when capturing.