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DivX 5.1 re-encoding with VirtualDub...

Discussion in 'DivX / XviD' started by Totenkopf, Oct 22, 2003.

  1. Totenkopf

    Totenkopf Member

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    Some questions:

    1. What should I do if on my second pass I get a bigger/smaller file size than the one I want? Do I just do another 'multipass-nth' pass with a bitrate adjustment + update log file?

    2. Under what circumstances do I have to do the 1st pass again?

    3. What filters do you recommend to increase quality when re-encoding?

    4. How do I determine what to set 'Max bitrate' to?

    5. What do you recommend for these settings: GMC, Qpix, and B-Frames and pyschovisual.
     
  2. powerdup

    powerdup Regular member

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    1. If you choose not to overwrite the first log file, then you can use that again and increase or decrease bitrate if needed.

    2. If you overwrite the first log file.

    3. In the way youre re-encoding you are not losing any quality since you are not using an previously encoded avi. Youre still encoding the vobs when you redo the nth pass based on the first log file.

    4. Im really not sure what codec youre but personally Ive never changed the max bitrate setting...

    5. If youre going for one cd, the B-Frames will really help with compression.
    Ive never used Qpel or GMC.

    Id recommend Psychovisual enhancements...I usually set mine to light. Of course this is with the 5.05 version so Im not sure how it works with 5.1.

    Good Luck.
     
  3. Totenkopf

    Totenkopf Member

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    Thank you for replying.

    I forgot to mention, I'm re-encoding an already encoded avi movie to fit it to a 700MB CD. Yeah, I know there will be some quality loss, this is why I need to know the best settings.

    I'm still a bit confused about 2-pass encoding, please tell me if the following is correct for doing subsequent passes.

    1. The original oversized file is always loaded for doing subsequent passes.

    2. I must do the 1st pass again if I update the log file. So under what circumstances do I have to update the log file (ie. when I modify the bitrate on the second pass from the 1st pass or something?) Is updating the log and doing the 1st pass all over again necessary for each subsequent passes?

    Thank you
     
  4. powerdup

    powerdup Regular member

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    Did you try to lower the filesize, before re-encoding the file?

    Example: Cut out the ending credits
    Lowered to bitrate of the audio

    1. Yes.

    2. Ok, Im sorry, about your first question in your first post, you just have to do another multipass with a bitrate adjustment + updated log file.
    Sorry if I caused you any inconvenience...Its been awhile since I did an encode and I totally misread your post.
     
  5. Totenkopf

    Totenkopf Member

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    Yes, I always re-encode the audio at a lower bitrate prior to re-encoding the movie, but I can't figure out why the GMC, Qpix, and B-Frames fields are ghosted.

    Also, the Mpeg layer-3 audio compression settings in VD only shows up to 24,000Hz for some reason.
     
  6. powerdup

    powerdup Regular member

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    Have you tried using only B-frames and not the other two options?

    Im not sure about Vdub's audio compression since ive never used it. I usually use CDeX for re-encoding my audio files.
     
  7. sumsaris

    sumsaris Member

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    Hoping this thread is not dead, I have a variant request to ask powderup. Is it possible to re-encode a divx/avi file to a higher bitrate and thus larger file in hopes of improving the overall image quality (smoothness, resolve artefacts, etc.) This assumes file space is not a problem and the original vob files are unavailable. And if so, how will this play with the inherent loss of quality due to a new generation en-code? thanks
     
  8. powerdup

    powerdup Regular member

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    Sorry, re-encoding will always lower the quality of the movie. Even if you use a higher bitrate than what was used before, youre still re-compressing the film and by doing so you lose bits which gives you lower quality. But you can use filters when re-encoding which can help hide the quality loss.

    If youve got a high quality source the degradation in quality might not be too noticeable especially if you combine the use of good filtering and lowering the resolution.
     
  9. sumsaris

    sumsaris Member

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    thanks powderup for your reply. If I assume my original avi file is decent what then would be the pre-processing 'filters' to apply in a program such as vdubmod or any other that would correct the specific problems of jerkiness and box artefacts. Post-processing in ffdshow hardly has any effect on these. In conclusion, do you believe then the trade-off between inherent quality loss in the new generation and the gain in refiltering basically results in a tie? And final question re/ 'something I heard': is it true that for a given avi file size, you may come across vastly varying quality, due solely to the fact that certain original sources (i.e. movies) compress more difficulty than others? What are the factors involved? Does VHS for ex. compress harder than dvd? Thanks again for your interest in the matter
     
  10. powerdup

    powerdup Regular member

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    Im not sure how to help with the jerkiness without more info on the problem but I can tell you that if the original file was interlaced and the encoder performed an IVTC then theres no way for you to get back the smooth playback.
    Smoother filters can help with the block artefacts.
    You can find some great filters here:
    http://neuron2.net/mine.html#virtualdub

    Yes and No.
    When yo re-encode a really great source using filters wisely you can achieve excellent results, however re-encoding a bad source will only give you bad results.
    Quality also depends on how yo perceive it. Some movies will look great to you while to others they look pretty bad. So, test out some sample clips of the movie with some filters and if they look good to you then you should re-encode. If they look worse, Id recommend keeping the movie as is.
    Yes. Movies that have many complex scenes like action-oriented ones tend to give the codec a hard time. Even something as simple as rain can give the codec a hard time in compressing the movie.

    I cant give you an answer about this question because I have no experience in compressing VHS tapes.

    No Problem.
     
  11. sumsaris

    sumsaris Member

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    Your comments were of great use. A Smart Smooth filter sample I tried worked so well that not only did it remove all the boxiness it also removed a mole from actor Jean Gabin's face and erased all the articles he was reading in a newspaper. I'm sure it's only a matter of finding the right dosage. As regards 'jerking', I probably should have used the term 'skipping'(as in frames). The phenomenom is similar to what you experience when you've got a weak processor or video card except in my case of course there are no problems with other videos. I might add the film in question is encoded under mp42 which I understand to be somewhat antiquated. Could this be responsible and if so what to do? Would the 'smart bob filter' help? Oh, and yes the films is interlaced (stopping the action shows the lines) but I have no clue as to whether or not IVTC has been applied or not.Thanks powerup.
     
  12. powerdup

    powerdup Regular member

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    Never used that codec before...

    If the video was interlaced, you can tell if it was IVTC'd by looking at the framerate. if its 23.976 it was if its 29.97 it wasnt IVTC'd but deinterlaced.

    Ive never tried the smart bob filter so I really cant help in that area...Have you tried using it so far?
     

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