HS2 recording defocussing

Ged

Active Member
Whilst recording footy on Sky to the HDD at SP,I have noticed that the recorded image is loosing focus detail, almost as if the bit rate is dropping off.
This is happening randomly when reording to the HDD and is there when transferred to a -R, if you record in XP it still happens but is less noticable.
For example the clock at the top left of the screen is a good marker, it may drift in other recordings but without such a reference it will be hard to spot.
Any ideas as what I can do?
 

Ged

Active Member
I have swiched the VBR setting to fixed and timeslipped Sky Sports News for the hard edged graphics and it seems ok..
fingers crossed.
Can anyone explain what limitations to setting the VBR to fixed may cause?
Ged
 

kenfowler3966

Active Member
Fixing is better if you want to download into a computer and edit later. Also some players dont like a variable bit rate as they cant handle the change in resolution
Basically the player when set to variable bit rate can drop to a lower resolution on a very complicated scene for a short time, and then change back later giving a better picture overall. By fixing it the complicated scene will become blocky as the amount of data required for a quality picture cannot be processed in the time available
 

Ged

Active Member
When the VBR was variable the Sky Sport Clock drifted in and out of focus, I have not noticed it since, I hope this is now OK.
During previous recordng the display became quite blocky/low res in it's resolution.
 

Ged

Active Member
I am still having problems.
I recorded the Derby with XP setting and it plays perfectly.
Dubbed to RAM a total of 1h45m with flexible rec.
I once again had the drop in recording quality, it drifts in and out of focus for no apparent reason, I am now dubbing with SP as this covers the time so I will check in the AM.
Does any one know why I keep getting this transient loss in picture quality/resolution?
As mentioned the origional is perfect, it is only the dub(RAM / DVDR) which is out.
Ged
 

PhilipL

Member
Hi

Does any one know why I keep getting this transient loss in picture quality/resolution?

It could just be a result of MPEG encoding. That is largely how it works. The encoder may be deciding that something static sat in the far corner of the screen isn't what is being watched, but the moving action is in the middle, and so the logo in the corner doesn't get priority encoding, with the result that when there isn't enough bits left, it is encoded at lower quality, which gives the effect of knocking it out of focus.

You get similar effects with peoples faces on lower rates, where the skin loses detail when the face starts moving, and the detail comes back when it becomes static.

Re-encoding is obviously putting the original through another decode-reencode cycle making this more obvious.

Regards

Philip
 

Ged

Active Member
Thanks Philip,
I have checked the second dub and it looks better, this was done set at SP, the editted match was 1h 45m.
So it seems there is a tade off and it comes down to one of the two;
allways record and edit in XP and either

1. dub with FR and get variable detail loss on sharper edges

or

2.dub with SP and get a softer yet more consistent image.

Ged
 

edz

Active Member
Hi all,

just a small point the "fixed" setting doesnt relate to fixed bit rate or constant bit rate, it refers to frame size.

When the bit rate drops too low or using time based recording if the unit is in variable it may reduce the recording frame size from 720 (or 704) x 576 down to 352 x 576 or even 352 x 288.

This will play back ok on the recorder but will be a headache if you want to extract the files and edit them without re-encoding.

If you change this setting to fixed it wont change frame sizes during the encode, the only disadvantage to this is if you are running low on space on your disk or there is a lot of heavy action on screen at a low bit rate you may get more macroblocks.

I dont believe you can make the unit record in a constant bit rate although XP mode will always provide a high bit rate throughout the recording.

Hope this helps


Cheers

Edz
 

Ged

Active Member
Thanks for the advice,
this has been a strange one and I am still not too sure why it should drift as it happens two to three times a match, or there abouts.
Like any intermittent glich, once spotted you tend to be looking for it all the time.
 

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