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Thread: Missing information on the Internet.

  1. #1
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    Default Missing information on the Internet.

    1. Ok a very simple question yet I cannot find an answer anywhere.

    I have some MPEG2 captures which I want to take a few scenes from.

    The file is 6gb for an hours worth, I just want a few scenes from it about 5-6 minutes.

    The catch?

    I want it at EXACTLY the same quality as the original 6gb MPEG2 file.


    I have Premiere and some other programs (virtualdub, etc) , yet this only allows me to save as AVI and AVI DV. I fear that these, even at the UNCOMPRESSED setting will lose some data. Again I just need the exact same quality as the original file.

    Say using Premiere how would I save the cropped file at EXACTLY the same quality as the original, preferably in the same codec, or in the most lossless and easiest to cleanup/edit codec possible.

    Where lies my answer?

    2. What is the easiest way to "clean up" and enhance video very well?

    I am very sorry if these are noob questions but I am a complete novice in video.

    Thank you very much for your time.

  2. #2
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    MPEG is a lossy format. If you trancode MPEG to MPEG, you will probably get a reduction in quality. I'm assuming you want to maintain the original video codec to create a DVD, but if you wanted to make an exact copy, use a lossless codec such as huffyuv. You won't notice a reduction in quality if you use DV AVI.

    In reality, if you keep a high constant bitrate and use a decent MPEG encoder, you won't notice any change in quality.

    Expirement.

  3. #3
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    Default

    Thanks so much for your quick reply!

    Basically all I want is to not lose any information when I crop my original MPEG2. I will try to export the cropped file as huffyuv under Premiere.

    If that doesn't work can you advise which is the losslessest format to export under Premiere. AVI or AVI DV? And which settings do I select,.. Drop frame...limit bandwidth,... there are so many under options.... Basically the few seconds of the MPEG2 that I cropped I want to save under the highest quality possible.

  4. #4
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    The term AVI is pretty generic. It's really just a term - if you're going to encode to "AVI", you'll need to choose a codec. And there's a plethora to choose from - from heavily compressed MPEG4 codecs such as DivX to losslesss codecs such a huffyuv.

    If you don't want the hassle of understanding all the options, go for DV AVI and download the Panasonic DV Codec.

  5. #5
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    Ok I'm learning fast. I installed huffyuv.

    In premiere it becomes available in export codec choices only if you select Microsoft AVI as the filetype. (Selecting AVI DV) will not let you choose it.

    My question now is there is also a check box for recompress (option "Maintain datarate" or " always.") This defaults to on, should this be switched off for huffyuv or doesn't it matter.

    Trying the Panasonic DV codec now.

  6. #6
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    Yep, DV AVI is an AVI that uses a DV codec

  7. #7
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    Ok seems I was talking bull.

    I cropped my 4 gb 1 hour 40 minute video to 3.39 seconds.

    I saved it as AVI, using huffyuv (maintaining original datarate).

    The three minute and thirty three second avi sitting on my desktop is 3.6gb.

    I had no idea lossless meant such a filesize.

    Gonna try the DV option and hope for a more realistic few hundred megs.

  8. #8
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    See if you can follow me.

    It isn't working,.. no matter what codec I use I still get some compression, (i.e. the ugly "squares").

    I don't understand.

    My 1 hour MPEG2 file is 3gb.

    So at that ratio 10 minutes should be 500mb,

    5 minutes should be 250 mb.


    Why is it that I cannot simply crop that file??

    I made a crop (total 5 minutes) logic says it should be 250 meg right?

    If I save as lossless huffyuv this 5 minutes = 3.6 gigabytes

    If I save as DV AVI (panasonic or otherwise) 5 minutes is = 300(!?) meg

    but with very ugly compression squares/blocks/artifacts, (full quality "no compression" selected, and maintain bitrate selected.)


    Why can I not simply crop my original file, keeping the little 5 minutes in the middle unchanged and just replace the start and stop bits so it's still an MPEG2, but unchanged!

    Why all this stuff that drives you crazy?


    Man your my only hope.
    Sager 5680 Notebook
    P4 3.2 HT
    512 Ram
    800 FSB
    5400 40GB HD
    Mobility Radeon 9600 Pro
    Adaptec Videoh! USB 2.0

  9. #9
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    Lets start from the beginning.

    Video is made up of series of picture frames; changes from one frame to the other creates movement - rather like the matchstick man flip book. If you flick the pages quickly enough, you see the little man dancing. In PAL video, 25 frames are processed every second. That's a lot of pages in a book

    Unlike our flip book, digital video is made up of data and the more data processed, the better quality the video. Unfotunately processing every single frame means the amount of data is HUGE. Lets imagine we scanned in every single page of our matchstick man and saved it as a Bitmap file. We want the video to last 5 mins, so thats 25 * 60 * 60 = 90,000 files. How many pictures do you have on your hardrive? Less than 90,000? Of the pictures you do have, how many are bitmaps? Probably none - they're all JPEG, right?

    We can reduce the file size of our scanned images by converting them to JPEG. This discards data that isn't needed to make up the picture, but so that the naked eye can't tell the difference. In practice, and depending on how much "compression" you want, the quality will degrade.

    So all of a sudden we've compressed our data and reduced the amount of space on the harddrive - we can discard the data to reduce file sizes. What happens if we then print the JPEG and scan it back in as a bitmap? We get back to the same scenario as before - huge file size.

    Now let's compare this to a lossless codec. To compress our video, we can use MPEG. But if we convert BACK from MPEG to a lossless codec, we're actually processing 25 key frames of data every single second. So our data actually goes up. But we won't loose any quality whatsoever. This is usually used during the capture process from RAW, analogue video to ensure you achieve an acurate copy of the original. This AVI is then edited and output as a MPEF etc

    You can however trancode to MPEG. This will result in a slight degredation of quality as you'll probably throw away more data. But in your case, it's the best way to go.

    So that leaves the question of why is the quality bad. Well, to answer that, I really need to know where you got the video from.

  10. #10
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    Thank you very much for your continued support.

    I understand fully what you have written.

    I will attempt to provide you with all the information in the hope that you will not get tired of me.

    I get my video as follows: A digital sattelite receiver is tuned to a sattelite which sends digital and analogue channels. This LNB feeds to an analogue tuner tuned to only 1 channel (I only need the one).

    This tuner uses a composite out signal to feed the analogue data to an Adaptec Videoh USB 2.0 Hardware MPEG2 encoder. This plugs into a P4 3.2 HT laptop via USB 2 (unfortunately firewire and PCI is not an option) . and captures twice daily 4gb streams off that sattelite.

    At the end of each day all I need is 5 minutes out of each 4gb (1 hour) feed.


    Now,... the captured MPEG2 is excellent quality, when compared to what I see on a reference LNB monitor. (Remember it's an analogue channel, so it isn't HDTV to begin with).

    The only problem is when I use an editing program to crop those 4gb 1 hour long files to a mere 5 minutes.


    My only options seem to be a huffyuv' 5 minute 3.6 gb file (which is huge and unuseable)

    Or a very artifacty looking AVI or AVI DV of around 300 mb.


    If I could just be home and simply CAPTURE only the 5 minutes that I need, then that MPEG2 stream is perfect, but I cannot.

    My only question is, can these 4gb MPEG2 files not be simply cropped without applying a decompression-recompression. I.e. just crop them as they are.

    I am at such a loss, I am contemplating a screen recorder of somesort to just play and screenrecord the 5 minutes that I need.

    *Any* advice is very welcome.
    Sager 5680 Notebook
    P4 3.2 HT
    512 Ram
    800 FSB
    5400 40GB HD
    Mobility Radeon 9600 Pro
    Adaptec Videoh! USB 2.0

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