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Size of recordings

A

Alandw

Guest
Hope this is not daft question but:-

I am thinking of getting the Sony RDR-GX3, but am a bit confused by how the recording size is specified. i.e on High Quality setting you get 60 mins, SP 90 mins etc. but would not the size of the recording depend on the type and quality of the material being recorded?

On my PC I have a Nebula DTT card, and when recording a 2 hour film, it takes up approx 2.5-3 GB in mpeg form (I don't think it is compressed in any way). I appreciate that the PC is recording the mpeg in digital and that the DVD recorder is turning analogue into digital but why the discrepancy in size between the two? (i.e a 2 hour film taking up 2.5 GB(uncompressed) in MPEG on the PC could not fit on 4.3GB DVD at High Quality setting)

If I look at the tech info for Nebula signals it gives a bit rate for the Video and Audio, which differ according to material and channel., so this explains some size differences for the PC recording with digital channels, but will analogue video always be the same size regardless of channel or material?

Thanks Alan
 

davee b

Active Member
The quality of the source material is irrelevant. the bit rate varies for each quality setting around 10mbps usually for top quality (1 hour recordings), 5 mbps for 2 hour etc etc. some machines will increase the bit rate momentarily to allow more data to be written for fast moving scenes. :cool:
 
A

Alandw

Guest
Ah thanks for that.

It just seems a bit odd that two recording that are both of the same material (a film say) and which end up in the same form i.e. mpeg should differ in size so much.;)
 

davee b

Active Member
If the films were both the same length and recorded at the same quality then they shouldnt have dramatically different sizes. i'm definitely no expert on this though :rolleyes:
 
M

Member 34135

Guest
When using a device like the Nebula you would be much better using a DVD writer installed in a PC, that way you keep the signal in the digital domain and it always looks as good as it was transmitted. The Nebula doesn't re-compress the signal it just records the mpeg stream.

Playing back a digital signal through a DAC and then through an ADC is really not the way to go as each stage adds noise.

Andy.
 
A

Alandw

Guest
Thanks for your responses.

I am not trying to copy PC recordings to DVD recorder, just wondered about the size difference between the two recordings.

The answer would seem to be that the DVD records at a fixed bit rate regardless of the material (and has to convert analogue to digital) which seems rather inefficient, as it takes up more space than would be strictly necessary for the same amount of information kept and stored in pure digital form.

Maybe you could say that analogue contains a infinite amount of infomation whislt digital is finite?

Alan
 

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