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Thread: Output Quality

  1. #1
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    Default Output Quality

    Hi there,

    I notice that when I output my video files to DVD from Mediastudio there is a loss in picture quality. Some clips are quite grainy. I have saved the files as MPEG NTSC DVD (29.97 fps) using Field order A and B and also frame based but all give the same results.

    If I plug my camera directly into my tv the quality is fine so I'm losing quality somewhere.

    Does anyone have any ideas?

    CK
    PC specs:
    Pentium 4
    2.53GHz 512 MB RAM
    120 Gig HD

  2. #2
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    Default

    Because MPEG2 compression is higher with MPEG2 compression compared to the source DV streams, the quality is inevitavly (but frequently unnoticably) worse. It all depends on the bitrate and GOP structure. The first thing to check is that you're outputting at the highest video bitrate for your length of movie - this would be something like a constant bitrate of 8000kbps for less than one hour.

  3. #3
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    Default

    Hi CK, good to see you back

    Young Marc is quite right, for best quality output you have to set your bit rate to the highest possible level. If your video is under an hour long then this should be around 8,000Kbps. The only slight difference of opinion I have with young Marc is that I have found slightly better quality results from Variable (rather than constant) bit rates. To check your settings in MediaStudio check the following steps,

    1. Open your project file

    2. Press ALT-Enter to check the project settings

    3. Select 'MPEG' for file format

    4. Click the 'Edit' button

    5. Click the 'Compression' tab

    6. For Media Type select 'NTSC DVD'

    7. Set Video Data Rate to Variable 8,000Kbps

    8. Click OK

    9. Click OK

    10. Render your movie and open the output with your authoring tool.

    Then all you have to do is make sure that the project settings in your Auhtoring Tool are also set to Variable 8,000kbps.

    Hope this helps. Please let us know how you get on.

    COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
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    Remember, there is always more to learn than there is to teach.

  4. #4
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    Default

    Ahh, but at a constant bitrate, quality will be better for a movie of less than 1 hour using PCM audio. My reasoning is thus: the DVD standard doesn't allow a bitrate higher than x. If you have a Variable bitrate, your video will go up to the bitrate but no higher. It will therefore be lower than this maximum at certain points in the video. If you fit your entire movie at the constant maximum bitrate on a DVD, then CBR is better than VBR. *phew*

  5. #5
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    Default

    Yes indeed young Marc, all of that is true. However VBR is in general terms more efficient and peaks the bit rate at the time the de-coder needs it. For example the comment below is typical of what can be found on many technical Websites.

    Constant Bit Rate (CBR) encoding sets a fixed rate of transfer for the video information. Whilst this is allowable, it is not an efficient use of the DVD-Video format. In scenes where there is little or no movement, CBR is wasteful as it encodes the signal into considerably more bits than is necessary. For difficult to encode scenes with lots of movement, the constant bit rate limits the encoded picture quality.

    Variable Bit Rate encoding (VBR) dynamically alters the bit rate used depending on the complexity of the picture to be encoded. For simple scenes with little detail and motion, the bit rate drops significantly. This reduces the amount of data to be stored and read in when playing the disc whilst still maintaining picture quality. This means there is more capacity on the disc to accommodate the higher bit rates needed to maintain picture quality for scenes with a lot of detail and motion. The practical upper limit for the VBR is the maximum data transfer rate available in DVD.

    Variable Bit Rate encoding is normally used when authoring DVD-Video as it delivers a combination of higher picture quality and longer playing times compared to Constant Bit Rate encoding.
    Of course the difference is often marginal. I suppose if CK's movie is quite short, he could try both CBR and VBR and see which turns out the best.
    COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
    Sony TRV33e : Sony TRV310e : Canon XM2
    Sony Vegas Studio editions to v11

    Remember, there is always more to learn than there is to teach.

  6. #6
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    Default

    Thanks people!!!

    I upped the bitrate to 8000 and that improved the quality. I tried both constant and variable with no difference in quality. I guess this is because my movie at the moment is only 20 minutes long.

    Is 8000 kbs the maximum bitrate for DVDs?

    Any other tips for highest possible output quality?

    CK
    PC specs:
    Pentium 4
    2.53GHz 512 MB RAM
    120 Gig HD

  7. #7
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    Default

    If I remember corectly the maximum bit rate is in excess of 9,00Kbps (9.8Mbps rings a bell), but I am sure others can advise of the specific figure.
    COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
    Sony TRV33e : Sony TRV310e : Canon XM2
    Sony Vegas Studio editions to v11

    Remember, there is always more to learn than there is to teach.

  8. #8
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    Default

    The combined maximum bitrate for audio and video in the white book standard is 9.8 I believe. So with PCM audio and 1 hour of video, you impose a limit of 8,000kbps on the video.

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