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  1. Member
    Join Date: Jul 2014
    Location: United States
    Search Comp PM
    Hi guys,

    So my understanding of frames so far is that there are three types of frames: I, P, and B. I frames are snapshots of what the video looks like at that moment. P frames have data for only the changes that have been made to a previously encoded I frame. B frames grab data from both an I frame before it and after it. In terms of compression, I frames are not very compressed, P frames are more compressed, and B frames are the most compressed.

    Key frames are a little more gray for me. They seem to be elevated I frames that allow for additional data. The only thing I know about key frames is a frame needs to be encoded as a key frame if you want to split a video at that frame.

    I am trying to split a VOB that I ripped from a DVD. I assumed that a VOB was more or less a "lossless" rip of video streams, so I would be able to split it wherever I wanted. I figured that every frame was an I frame and/or a key frame. This seems to not be the case, so I was wondering how I would go about ripping a VOB to encode in either all key frames or with a clump of key frames around the area I would like to split the video.

    Thanks,
    Abbott
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  2. Member
    Join Date: Mar 2011
    Location: Nova Scotia, Canada
    Search Comp PM
    "I figured that every frame was an I frame and/or a key frame."

    An I-frame is a key frame. Much confusion here.

    What you want is smart cutting of DVD compliant mpeg2 video. I think TMPGEnc will do this, and avidemux may. Try searching.
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  3. Member
    Join Date: Jun 2012
    Location: USA
    Search Comp PM
    Specifically, TMPGenc Smart Renderer will reencode/create the necessary keyframes and not touch the stuff it doesn't have to -- but what is your goal here? To make another DVD?
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  4. Member
    Join Date: May 2005
    Location: Toronto ||*||
    Search Comp PM
    Hi,

    I'm not going to get into the pros/cons of encoding intra-only video but here's a few quick answers for you.

    two methods that come to mind for keyframe based copying are:

    1 dvdshrink's set start/end frames. Use for chapter or frame extraction (frames are intra).
    2. Avidemux. Let it index then set your in/out keyframes.


    Modern DVD's use MPEG2 compression (but possible to use mpeg1) and it does use frame prediction encoding ( I B P).
    It's possible to encode MPEG2 and/or MPEG4 video with intra only frames by telling ffmpeg to encode 'intra' only. Check ffmpeg
    docs for more info.


    Hope this helps.
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  5. Member
    Join Date: Jul 2014
    Location: United States
    Search Comp PM
    Originally Posted by Hoser Rob View Post
    An I-frame is a key frame.
    That makes things so much easier to understand.

    Originally Posted by VirtualDoobMon View Post
    It's possible to encode MPEG2 and/or MPEG4 video with intra only frames by telling ffmpeg to encode 'intra' only.
    This would be a "lossless" rip that I was expecting originally right? I imagine the size of the video would be a lot bigger, but I would be encoding it later so it's only a temporary problem. Are there any other downsides to this?

    I am ripping this DVD to MKV for my HTPC. Won't using a re-encoding tool like that cause artifacts or other problems because it is transcoding already encoded frames? Especially because the frames it would have to transcode would be the compressed p and b frames?
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  6. The only way to get an all I frame MPG would be to re-encode it with I frame only GOP, but then you would have a non-DVD compliant file that you would have to re-encode to be DVD compliant; bad news as far as quality goes.

    Like Hoser Rob and smrpix said TMW is the tools for you; the smart rendering will only re-encode the part that didn't fall on an I frame.

    Other tools that could work are TDA (will only cut on I frame, limits accuracy to 0.6 seconds), Videoredo (not sure, this one might have smart rendering) and Nerovision (this has smart rendering, they call it ultra-buffer and you may have got it with your burner).
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  7. Originally Posted by Abbotta4 View Post
    I am ripping this DVD to MKV for my HTPC. Won't using a re-encoding tool like that cause artifacts or other problems because it is transcoding already encoded frames? Especially because the frames it would have to transcode would be the compressed p and b frames?
    You should have mentionned that first, that changes everything. What VirtualDoobMon suggested is better, trim the DVD with Shrink/Recode after you rip it with DVDfab, then convert to MKV.

    No, you won't cause artifacts if you convert with a high enough bitrate; don't try to fit a movie onto a CD!
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  8. Member
    Join Date: Oct 2004
    Location: Freedonia
    Search Comp PM
    If the OP wishes to cut his video, or "split" it as he puts it, both the old MPEG-VCR and VideoReDo are fine choices that won't screw up his quality. Both will understand VOB.

    Since the ultimate goal is to get to MKV, then MakeMKV would be fine for that. Just keep installing the latest beta every time it expires and it will remain free. In such a case of DVD -> MKV I'm not really seeing the need to split the video unless he's trying to do something like nic2k4 suggests and put this on a CD or a really small flash drive.
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  9. Member
    Join Date: Jul 2014
    Location: United States
    Search Comp PM
    The DVD I am ripping is a TV Show season that I am splitting to episodes. I would like to encode with MeGUI so I can preserve consistent quality across all episodes. 23/24 Episodes are split and encoded correctly, one episode has content at the beginning that I would like to crop out. Would DVDShrink's set start/end only encode intra where the video needs to be split? That way I can still encode the end product with MeGUI. Or would the whole file be encoded as intra and then I would be encoding a second time, which opens up the possibility for visual errors?

    Thanks for answering all my questions so far and so quickly!

    Edit: I guess it's silly to ask this because this is exactly what TMPGenc Smart Renderer does. I will split with this tool and then encode with MeGUI.
    Last edited by Abbotta4; 22nd Jul 2014 at 13:01.
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  10. Something to keep in mind, all scene changes happen on I frames. That means the extra content at the beginning of that episode should be easy to remove. Shrink does not encode per se, it transcodes and causes a loss of quality in the process. If you set the compression to 100% there won't be any loss and as a bonus you can un-check the deep analysis and high quality encode options. A better alternative to splitting the epsiodes with Shrink is to select only the chapters for 1 episode at a time when you rip the DVD and save to separate folders.

    Have you tried to trim your MKV? SolveigMM AVI Trimmer + MKV can do that and it's lossless, the only issue is it only cuts on I frame and they can be pretty far apart on these kinds of files; the damning bit with it, is that it will seem like it will cut where you want, but it will actually do it on the following I frame. The key here is you have to seek the nearest keyframe to your cut and hope it works out.
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  11. Member
    Join Date: Jun 2012
    Location: USA
    Search Comp PM
    Originally Posted by Abbotta4 View Post
    Edit: I guess it's silly to ask this because this is exactly what TMPGenc Smart Renderer does. I will split with this tool and then encode with MeGUI.
    No need for MeGUI, TMPGenc will smart render directly to MKV if you tell it to.
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