All the questions I’ve always wanted to ask and never dared…

[David Roth weiss]

[Paris_ntz] ” 2. What is Uncompressed HD? Meaning: since HD is not analog, its digital, therefore encoded, therefore there has to be a codec, therefore there has to be some kind of compression?

The term uncompressed is used quite loosely and inaccurately (technically speaking) in both SD and HD to cover any number of high quality formats, essentially all of which are actually somewhat compressed.

There really is no such thing as uncompressed HD, at least in most cases for most users. Even the cameras with the absolute highest resolution, recording at the very highest bitrates, have a compression stage before the signal is recorded. There are of course ways to bypass the cameras electronics, sending a truely uncompressed signal directly to hard drive, but most of us are using tape-based or P2 based cameras, all of which compress the signal in order to make the recorded data smaller in size, easier to store, and faster to transmit.

There’s at least part of the riddle out of the way for you I hope. Hopefully others will answer more of your good questions.

DRW

[Martin Baker]

3. HDCAM format: is it a codec too? Meaning: DVCProHD is a format you can natively edit in (there is no “capture” just a transfer of 0’s and 1’s from tape to hard drive). Do you have to transcode in some way what is HDCam on the tape to something digital but different? (not sure if Im being clear here)

Sony use hardware to compress and decompress the images to/from tape, but unlike Panasonic they do not currently made their HDCAM codec available to third parties (and are unlikely to). In the past it was possible to do native HDCAM editing with Sony’s own Xpri system (which is no longer being developed). Also Sony did flirt with Discreet in 1999 to implement HDCAM codec support but this seems to have been dropped too. So the bottom line is that in 2006 you interface to HDCAM with uncompressed i/o and the VTR compresses/decompresses the image for tape. It is not possible to work with the format natively as you can do with Panasonic solutions.

5. Lots of DVD players in Europe (well, at least in France) offer a choice between RGB and YUV. I somehow understand that YUV is PAL, while RGB is PAL or NTSC-agnostic. When should you render in RGB, when should you render in YUV, if youre going to DVDs or youre delivering to the web?

I think you’re confusing outputs on the player from the data on the DVD. YUV and RGB are used in both PAL and NTSC. All DVDs are encoded as YUV MPEG-2 so if you’re talking about FCP’s sequence settings, then you should be YUV all the way. Same for web – the end codec will convert to RGB if it needs to.

7. Whats the difference between, on one hand,choosing the sequence settings (selecting the sequence and apple-0) to be anamorphic 16:9, and, on the other hand, choosing in the same menu (apple 0, sequence settings) the quicktime video settings in compressor DV-Pal advanced button, the aspect ratio at 16/9?

The aspect ratio setting in the Advanced section does not affect the FCP sequence at all. It gets overridden by the Anamorphic checkbox. However, if you do an Export > Using QuickTime Conversion, then the Aspect Ratio setting in the export settings will determine the aspect ratio of the file when displayed in QT Player or if imported back into FCP.

Martin
Digital Heaven, London UK
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[Glenn Chan]

1. Why is HDCam’s 3:1:1 better than, for instance, DVCProHD’s 4:2:2? I thought the higher the numbers, the better the quality?
The x:x:x notation (or J:a:b) mostly refers to the ratios between the luma samples to the chroma samples.

HDV1 1280x720p 4:2:0 Luma res: 1280×720 Chroma res: 640×360
HDV2 1440x1080i 4:2:0 Luma res: 1440×1080 Chroma res: 720×540
DVCProHD 1280x720p 4:2:2 Luma res: 960×720 Chroma res: 480×720
DVCProHD
30fps 1920×1080 4:2:2 Luma res: 1280×1080 Chroma res: 640×1080
25fps 1920×1080 4:2:2 Luma res: 1440×1080 Chroma res: 720×1080
HDcam 1920×1080 4:2:2 Luma res: 1440×1080 Chroma res: 480×1080

HDCAM has a higher bitrate than Panasonic’s DVCPRO HD format, so this means that HDCAM is recording more information to begin with.

2. What is Uncompressed HD? Meaning: since HD is not analog, its digital, therefore encoded, therefore there has to be a codec, therefore there has to be some kind of compression?
Uncompressed usually refers to digital video that doesn’t have DCT-based, JPEG, MPEG, lossless compression, or other forms of compression (excluding chroma subsampling). 4:2:2 uncompressed video will go over SDI, while other forms of video will not.

4:2:2 chroma subsampling itself behaves very much like compression. Marco Solario’s site shows the differences between different 4:2:2 “uncompressed” codecs. codecs.onerivermedia.com
4:2:2 chroma subsampling, in practical situations, is usually not noticeable at all.

7. Whats the difference between, on one hand,choosing the sequence settings (selecting the sequence and apple-0) to be anamorphic 16:9, and, on the other hand, choosing in the same menu (apple 0, sequence settings) the quicktime video settings in compressor DV-Pal advanced button, the aspect ratio at 16/9?
When you add a clip to the timeline, FCP will look at both the clip’s settings and the timeline’s setting. If necessary, it will apply the correct “track motion” (distort) to the clip to make it match. Changing the anamorphic setting of a clip already on the timeline doesn’t seem to change its look- you should go into track motion and change things, or paste attributes onto that clip.

An anamorphic sequence will change the look of the canvas window to show the image in 16:9 ratio (instead of 4:3).

9. When you say 8-bit or 10-bit uncompressed, what are those 8-bits or 10-bits?
These bits refer to the bit depth of the video. It’s a similar idea to audio being 16-bit bit depth or 24-bit bit depth.
10-bit reduces the amount of rounding error. Rounding error can occur in places such as the conversion from R’G’B’ color space to Y’CbCr (many people incorrectly refer to Y’CbCr as “YUV”).