Do HardDrive/dvd recorders record at Full DVD quality...?

Discussion in 'Blu-ray & DVD Players & Recorders' started by ancient, May 15, 2005.

  1. ancient

    ancient
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    Hi...

    Just looking into buying my first Hardrive/dvd recorder.

    I'm interested in recording from sky/tv at Full dvd quality (on Hardrive) and then transfering it on to a dvd blank disc (again retaining full DVD quality).

    From what I've read all units have different recording qualitys ie xp, sp, lp etc...

    Obviously the highest quality is the best...(I'm assuming full dvd quality?) but when you transfer from Hardrive to DVD disc at the highest quality you can only get 1 hour of recording unless you go one lower and then get 2 hours.

    1 hour not good enough for movies!

    Will the one down from the top setting still be full dvd quality...?

    Have also read about a new panasonic 50 model,that it records onto Hdrive at a higher qulaity than dvd...?(I could then lower that setting and get more time on a disc?) do any others do this...?

    Please advise...
    Thanks.
     
  2. Rasczak

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    Have a look at this FAQ. Sky is a low bitrate source and your DVD recorder receives a decent RGB signal. Nevertheless it is encoding an analogue source and thus you will start to notice a drop in quality as you work down the modes. I try to avoid putting more than 90mins on a DVDR although, again, if the movie is longer than that you have to compromise.
     
  3. ancient

    ancient
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    So...it sounds like I should wait for the new Sony ones D710 which will record onto Dual Layer....?

    Cheers.
     
  4. ancient

    ancient
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    Have also read the panasonic 50 model records at full resolution for 4 hours on a normal disc...?
     
  5. Rasczak

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    Yes they do.

    If you want - obviously double the space will mean you will be able to use higher recording modes for longer.
     
  6. gavan

    gavan
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    Depends what you mean by 'DVD Quality'. I've seen some DVDs with superb picture quality, others with rubbishy encoding and loads of artifacts. It all depends on how well the material was encoded during the mastering process.

    Personally, I find that the 'SP' (2 hours per single-layer DVD) mode of my Panasonic EH-50 appears to make 'perfect' copies of the input signal from Sky or any other source that I've tried.

    With 'dual layer' recorders in the pipeline, it's not unreasonable to expect that you'll be sson able to put 4 hours of high quality recording onto a home-made DVD.


    Gav
     
  7. Loobster

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    Agreed. There is currently no UK broadcast source that is of a high enough quality to take advantage of any mode "higher" than two hours. It's perfect for archiving Sky+. And of course any DVD movie backups should be done on the PC.

    --Loob.
     
  8. ancient

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    Quote:
    Have also read the panasonic 50 model records at full resolution for 4 hours on a normal disc...?


    "Yes they do."

    So how is it possible they can achieve this;as every other make can only fit 1 hour of high quailty...?

    Thanks for any input guys.
     
  9. Rasczak

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    Absolute rubbish. UK Digital TV may be low bitrate but we are recording the analogue output. Thus the higher the bitrate the better. I can certainly see the difference between HQ, HSP and SP modes (or equivalent) when recording high action scenes. Just because you can't see the difference on a 28" TV Loobster doesn't mean it doesn't exist.
     
  10. Loobster

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    It's not.....

    --Loob.
     
  11. LV426

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    Terminology. You can indeed fit varying amounts of full resolution video on a 4.7gb (single layer) DVD.

    "Standard play" is full resolution at a given compression rate which produces a file size from 2hrs video that will fit on a 4.7gb disc. With increased "quality" settings (above "standard play"), what differs is not the resolution, but the rate of digital compression used. Less compression = less likelihood of mpeg artefacts; not greater resolution. The way the soundtrack is encoded may also differ. On my Pioneer, at the highest bitrate (= shortest play time) setting, it uses PCM audio rather than Dolby Digital. This is lossless (unlike DD) but takes up more data.

    For the most part, less compression (only) may well be undetectable to most viewers.

    Getting more play time on a given disc is a matter of reducing the data needed (file size). This can be done (to an extent) in two ways

    - either by reducing the resolution (half as many pixels means half the file size, or twice the play time, all other things being equal)

    - or by increasing the amount of digital compression (reducing the data rate). More compression (alone) means greater likelihood of digital artefacts, but not less pixels (resolution).

    or a combination of both. The super-long "extended play" setting may well halve the resolution in both directions (quarter the file size, quadruple the play time) and apply lots of compression, too.
     
  12. ancient

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    Cheers guys.
     
  13. phelings

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    I have been tryingto get this through to Loobsters thick skull for months at Digital Spy.
    While we admit that there could be much better quality on Sky,its obvious to most that no matter how poor the various channels are,recording them in XP will offer superior results to recording in SP.Loob(and others) seem to think as Sky only broadcasts at around 5Mbps its not worth using 10Mbps to record it.Only true with genuine digital to digital recording-which we cannot presently do on a set top.
    Using Loobs twisted logic would mean recording from a VHS tape in EP and from low bitrate channels in LP as "its not worth recording in XP".
    Admittedly,most movies look fine in SP,but a one hour programme definitely looks better on dvd in XP(FINE).
     
  14. Rasczak

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    Loobster, by his own admission, has a 28" CRT. Notwithstanding that 28" CRT are hardly the be all and end all of reference status, they are also too small to accurately access PQ. A 28" TV is around 50cm tall - and the screen is smaller - we'll have people accessing quality from mobile phones next!
     
  15. LV426

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    I'm not totally convinced of the wisdom in recording VHS material at "fine" settings.

    I accept totally that the noise (etc) coming off such an analog source will increase the likelihood of compression artefacts for a given compression setting. So I can see the logic behind using as little compression as possible.

    However (using my Pioneer as a basis, and using the manual "quality" values) as you reduce the "quality" value down from its best (1 hr per DVD = "fine = "MN32"), what happens is:

    first, the compression increases whilst retaining full resolution until you get to MN19, which is a bit below Standard Play.
    then, from MN18 downwards (until MN7), the resolution is halved in the horizontal direction only; vertical resolution remains at the full 576 lines.

    At this point (on the Pioneer, on a video mode DVD) the play time that can be put on a 4.7gb disc is 150 minutes, which is a little over twice what "fine" offers. However, much of this increase (up to 120 minutes, in fact) can be directly attributed to halved resolution. Or, to put it another way, the level of compression applied is actually equal to that applied at (Pioneer speak) MN29 quality (75 minutes, much higher than Standard Play but not quite "fine"); only the resolution differs.

    Now, given that the maximium resolution achievable from VHS is about 250x576, and SVHS about 350x576, and given that the resolution on a DVD produced in this way is 352 x 576, that would seem to me to more than adequately cover the incoming signal, whilst applying almost minimum compression.

    There seems little point in encoding a 250 (or 350) x 576 source at 704 x 576. Indeed, I'd contend that, for such a source, using the highest manual value, just below the resolution threshold (which on the Pioneer is MN18) would actually produce a better result than Standard Play (MN21) by using less compression. Yet allow 150 minutes to fit on a single disc.

    It may even be the case that halving the horizontal resolution actually reduces the impact of noise in the signal as well, thus reducing the impact on the compression process.
     
  16. EN

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    I made a test recording from same scene from VHS tape on HSP, SPand LP mode on my ex-SONY recorder 900. I was suprised from the result. I can hardly tell the difference in rezolution at all. But when recoded in SP mode I found more block structure than in SP mode in same frames. In HSP mode there as no block structure and the record was fine. So, I copied all tapes in LP mode.

    About PQ recording from TV. Lately I record 4h program so I can watch it later. One of the movies is some stupid "action" series SHE SPIES. I have noticed that in the movie there has been a lot of fast changing frames, so in SP mode I used blocking structure made picture very bad to watch, it was so obvious.
     
  17. TobyW

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    My own observations don't support that statement, especially when I use a good quality monitor.

    Let's try to explore the theory. It goes something like this. (Just speaking from memory, so don't quote me!)

    For a PAL signal, the broadcast video bandwidth is around 5MHz, depending where you live. At that rate, you could transmit a 5 MHz sine wave on a scan line and see it as a horizontal series of bright and dark points, at 10 points per microsecond. A horizontal line is roughly 50 microseconds long, so you could show roughly 500 bright and dark points on a line.

    Now, in the analog world, the term "lines of resolution" refers not to the whole line, but only to a part of the line that's equal in length to the vertical height of the picture. So for a 4:3 aspect ratio, our 500 points would yield 375 "lines" of resolution. (Remember I'm talking rough figures here, so don't quote these numbers!)

    Likewise, a VHS machine of 250 lines can display 333 black and white points on a horizontal line. Notice I didn't say "dots". These are sine waves, remember!

    Now, suppose you display a series of such lines, in which each line is offset a fraction of a dot from the line above it, like when displaying a diagonal edge. When you digitise the line, the sampling points are exactly above each other, so to capture the diagonal edge there must be enough sampling points to follow the slope of the edge on successive lines.

    If you only have 352 sampling points, you won't follow the edge. You won't even follow small variations within a given line. As an extreme example, suppose a good quality VHS generates a sine wave of 352 bright and dark points on a line, and your 352 samples happen to be exactly in the middle of the transitions between points, all you will capture is a line-full of gray samples.

    So if your VHS is any good, 352 x 576 definitely won't capture it all.

    On a historical note, there is of course a similar limitation in the vertical direction. From the early days of broadcasting this was recognised by applying a fudge factor, called the Kell factor, when working out what bandwidth was needed to transmit with a horizontal resolution similar to the vertical resolution. The Kell factor was 0.7 so for a 4:3 aspect ratio and 576 displayed lines, the broadcast number of dots on a line is 576 x 0.7 x 4/3, = 537 elements. That's why the video broadcast bandwidth is 5 MHz or so (as above).

    As I said, this is from memory over my lunch at work, so don't quote me!
     
  18. LV426

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    Perhaps I have to defer to greater knowledge here. It's certainly the first time I've seen the "250 = 330" detail. But I'm a bit puzzled by the segment about following diagonals.

    I understand what you mean about the slight offset as it applies to the original content of the line, assuming sufficient bandwidth to resolve it. However, surely it is not the case that the properties of the line itself (i.e. its ability, if I may use that term, to change shade) are offset? Is it not true that the sine wave to which you refer is of fixed frequency and varying amplitude? And that each line's sine wave occurs directly above or below that of the adjacent line? Then the only difference (aside from frequency) between the analog medium, VHS, and a digital medium, is that the one is a sine and the other is square. In other words, the inability to follow a diagonal already exists in the VHS source as each cycle of the waveform is directly above (or below) those of the adjacent lines.
     
  19. TobyW

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    Sorry to have confused you. This would be true if you looked at the RF signal, before the tuner demodulates it and converts it to plain video. The video signal is said to "amplitude modulate" a "radio frequency carrier" sine wave at the broadcast transmitting station, and the receiving tuner retrieves the original video signal, discarding the carrier. VHS recorders also modulate a carrier, but it's frequency modulation instead of amplitude modulation, so there is no correlation of the carrier from one line to the next.

    I didn't mean to suggest that every line consists of a 5MHz sine wave with varying amplitude. Rather, I was using the 5MHz sine wave to illustrate the fastest rate of change of the brightness across a horizontal line.

    To put it another way, a white-to-black or black-to-white signal transition is not an instant step-shaped edge. Rather, it's gradual, being directly restricted by the available bandwidth. Crudely speaking, a 5MHz bandwidth restricts the fastest possible transition time to about 1/500 th of a line length, so you can only cram 500 transitions into each line.

    A typical line won't contain any actual sine waves. Instead, the waveform will fluctuate in a seemingly random pattern, corresponding directly to the brightness fluctuations that you can see along the line. So if there's a regular pattern of near-vertical stripes in the picture (often called a "picket fence"), it's perfectly possible for a series of dots on one line to fall between the dots on the next line.

    Hope this helps.
     

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