Sony HQ+ and re-encoding technical question

Discussion in 'Blu-ray & DVD Players & Recorders' started by johnmccoy, Oct 30, 2005.

  1. johnmccoy

    johnmccoy
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    As a general principle I know you should not encode a signal twice, so I always copy to the HDD in the compression mode I'm going to use when writing to DVD.
    However I read on another thread that the Sony HQ+ mode is designed in a way that if you record to the HDD using this then re-sample down to the bitrate that fits the DVD, you get a better encoding than going straight from the broadcast to final mpeg. I can't see this in the manual or elsewhere and can only quess that this is like doing a two-pass encoding somehow.

    Does anyone know if this is true and why it would be so? Has anyone had the time to do some tests to see if it is better this way? If not I will try to find the time to do experiments myself, but that could take a while and I would really like a technical explaination.

    Thanks
     
  2. geekdude

    geekdude
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    If you record using the HQ+ mode. You record on the HDD at 15mbps. In addition the video additional information which is called complexity data is recorded. This is used to identify areas of the video where a higher data rate is required and also where less data can be used. When dubbing from HDD to DVD this data is used to vary the data rate of the copy so more data is used in areas with high picture complexity e.g Fast movement or fine detail. This means that the data rate can swing over a grater range and therefore give better picture quality than recording straight to DVD at the highest rate. Hope that makes some sort of sense.
     
  3. musukebba

    musukebba
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    It's a two-pass encoding, rather than a single pass. This will indeed give a better end-result.
     
  4. johnmccoy

    johnmccoy
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    Thanks for that - where did you find out about the complexity data? I'd like to read up on this in more detail if possible. However, it looks like I'll be recording things this way from now on.
     
  5. geekdude

    geekdude
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    The complexity date is generated during the encoding it indicates the frequency or detail in the image. It is a bit like a Speedo in a car it indicates how fast or how complex the data is. www.mpeg.org is a good place to start.
     
  6. ArtS

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    Manual (Euro version on page 73) says:

    "When a title recorded to HDD in HQ or HQ+ mode is converted to another mode, the recorder automatically assigns an appropriate bit rate, thus retaining the original picture quality as much as possible."

    It is enigmatic info, but it suggests that recorder uses two-pass encoding method when reencoding from HQ or HQ+ to others. I used this method yesterday. First I recorded title in HQ+ mode, then reencoded to HSP (1.5h) mode on DVD. Results are impressing!.

    I'm going to experiment with original DVD and I'm going to compare the same material recorded directly in HSP, SP, LSP, LP and maybe in EP mode to material recorded in HQ and HQ+ and reencoded to above modes.

    Pay attention - I think reencode from HQ+ to HQ doesn't make sense because HQ mode uses approx. 9 mbps bitrate, which is maximum value for DVD standard and encoder cannot use variable bitrate.

    ArtS :cool:
     
  7. johnmccoy

    johnmccoy
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    Thanks for all the replies everyone. I found this on the Sony UK site:

    "The Sony ... DVD recorders feature recording in HQ+ mode
    By recording on the hard disk drive at a rate of 15Mbps, you can achieve recordings at a higher quality level (HQ+) than DVD discs.

    When you want to dub HQ+ recordings to a DVD disk you can use Dynamic Variable Bit Rate (VBR) dubbing. Dynamic VBR captures quick & complex motion footage more precisely, offering superior quality DVD recordings.

    Dynamic VBR Dubbing uses an adaptation of 2-Pass Encoding Technology, which is used by commercial production companies to author pre-recorded DVDs."

    I look forward to seeing the results of ArtS's tests. I wish this had been made clearer in the manual as I will definitely start using the recorder this way from now on.

    This seems to be a major plus point for Sony in the quality stakes - do any other manufacturers offer anything like this that you know of? I was regretting not getting a recorder with a flexible record option, but this makes me feel better about buying the Sony machine!
     

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