I used to capture MPEG2 video with my Hauppauge WinTV-PVR-150 and the capture resolution was 720x576. The MPEG2 video captured with my recently bought Panasonic DMR-EH50 has the resolution of 704x576. I've noticed that other DVRs produce 720x576 videos... So, why does the Panasonic do this clipping? Is it possible to configure the unit to record in 720x576? Isn't the 720x576 resolution more "standard" than 704x576?
Thanks in advance!
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Thread: Why only 704x576?
704x576 is an official video DVD size. Why Panasonic chose it instead of 720x576 is something their engineer's would have to answer. Possibly it is to squeeze a little higher bit rate for longer recordings thereby providing slightly better picture quality.
704x576 is the official digital video size for TV. 720x576 is the official digital video size for DVD. !6 lines in DVD are just blank lines and are not read.
704x480 is broadcast standard. 8 pixels on each side of the image are added to pad the resolution to 720. This is done to protect the sides of the 4:3 image from horizontal phase shift during dubs and transmission. If you record broadcasts in 720 you typically get noise on the outer edges. These are pad pixels, and can be cropped without affecting pixel aspect ratio. To transfer to DVD you'd typically crop to 704x480 and store it that way, or add your own padding to make it 720x480. The Panasonic units (most of them) essentially crop for you by not capping these pad pixels. It makes sense. Quality should be slightly better. But to answer your question, no I don't believe there is any way to cap in full 720x480 resolution using that unit.Been around the world and found that only stupid people are breeding.
The black strips (left and right) shown here are the extra 8 pixels on each side to when capturing 720x480/576.
4:3 broadcast is always 704. This includes ATSC standard definition digital broadcasting.
And 704 and 720 are BOTH "official" for DVD.
Thank you very much guys!
With the Hauppauge card, that captures in 720x576, I never noticed any noise at the edges, either from cable signal ou VCR. So, isn't Panasonic being a bit exagerated? With this little "differente", they are able to get a slight increase in picture quality per file size, relative to other manufactureres... At the expense image information! Isn't this just a marketing move?
I'm worried because of the amount of information "loss" that each module introduces from the signal source to the TV! The DVD recorder clips the edges, the TV oversans, etc.. The result is that sometimes, in programs with subtitles embedded, the subtitles are clipped, losing some letters on each side in long sentences! This is really annoying...
Originally Posted by Cirruz
You see the blanking edges in a window on a computer but it gets lost to overscan on any TV. It's hard to argue that capture to 704 improves MPeg quality since the 16 pixels are mostly black and consume little motion bitrate. Panasonic is doing a favor to computer geeks by cropping the black edges 704.
Ok, I got it, thanks edDV. BTW, what's the software you got that last screenshot from?
Some other thoughts on 704 vs 720 and DVD. Both use 13.5 MHz. sampling so the difference is the width of the capture.
Most consumer equipment including DV camcorder pass through and DV transcoders such as the Canopus ADVC will capture 704x480/576 broadcasts and VHS dubs at 720x480/576 and thus have the 8 pixel left and right blanking edges in the capture.
If you encode this as 720 to a DVD, you get the same black edges on the DVD but the broadcast pixels are spatially 1:1 to the DVD. If you crop to 704, you should encode as 704. If you crop to 704 and then encode to 720, you will be scaling 704 to 720 (i.e 2.27% H upscale) and this will have some interpolation artifacts.
If you intend to encode 352x480/576 you should crop to 704 first since 704/2 = 352. If you convert 720 to 352, you will have the black edges and be downscaling at an odd interpolation of 48.89% rather than the ideal 50%. 50% will be sharper than 48.89%.
The reason why 704 is used is that it is the closest "digital" reference to the analogue signal of 702. 720 is used for digital broadcasting - assuming that the source is a digital signal and not just converted analogue. I think the reason why Panasonic chose to record at 704 is that they thought most people would be recording analogue sources (off air TV, satellite) and wouldn't have access to digital TV signals. Of course this has now changed, but as has been said above, I would worry too much about loosing the 16 pixels as no appreciatable picture is lost. To downconvert to half D1, just loose 8 pixels eitehr side to make it 704x576 and then its a straight 50% resize.
Originally Posted by energy80s
For N. America, Cable SD MPeg2 "digital channels" seem to be all 704 as well.
I'm not sure how other countries are planning to do it. There may be local deviations.
PS: Another confusing legacy issue: true analog NTSC as historically recorded to broadcast tape and sent over air had 486 lines. The FCC actually issued warnings when early digital equipment used 480 lines but soon relented. 4:3 aspect required 648x486 which was difficult to handle with a computer.
In the UK BBC uses 720x576 for all digital txs, ITV & Channel Four use 704. The Original Analogue txs were officially 702 wide. Now a lot of stations use 544 (ie. ITV on satellite) as they are using such low bitrates that a higher resolution would macroblock all over the place! This is for both 4:3 and 16:9 images.