Latest post Thu, Sep 27 2018 6:19 PM by Lukas Boeck. 3 replies.
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  • Thu, Sep 27 2018 11:43 AM

    • Roger Owen
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    Import MP4

    Hi all, I have to input some MP4 material to work mainly on the audio. I want to maintain the best picture quality, but without overloading my systen by Inputing at 1:1 MXF. I've analysed the MP4 files (with the very clever 'Media Info' Ap), and 1200 Kb/s bit rate is shown. Seems to me that there's little point in inputing any higher than DNxHD36......or, am I wrong here?

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  • Thu, Sep 27 2018 2:04 PM In reply to

    • BarkinMadd
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    Re: Import MP4

    Depends on what you are trying to do. If you want to work with a light-weight proxy for editing then you would link (not import) to your MP4 and transcode to DNxHD36. Then you can edit using the light-weight proxies and when you want the final output, relink your sequence back to your original source MP4s and output the sequence in whatever quality you wish... The key is that you aren't locking your decision of output quality early in this process.

    Does that make sense to you or am I misunderstanding your use-case?

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  • Thu, Sep 27 2018 2:41 PM In reply to

    Re: Import MP4

    36 Mbps of an intra-frame codec like DNxHD is not really comparable to the same rate (or even lower!) of an inter-frame or long-GOP codec like AVCHD.

    Intra-frame codecs like DNxHD, ProRes, AVC-Intra, and others perform better (i.e. faster scrubbing, playback, etc.) because each frame is self-contained - there's no calculation being done in reference to nearby frames.  However, that means greater file sizes and data rates are needed in order to achieve the same level of quality.  36 Mbps of DNxHD will look far worse than similar (or even lower!) rates of codecs like AVCHD and XDCamEX.  With these codecs, file sizes are smaller because frames are generated by having a single large "I-frame," surrounded by a little group of other frames that reference the I-frame.  Great for saving space on a media card in your camera.  Not so great for fast scrubbing and editing (though XDCam is Avid-natively supported and does work pretty well).

    So, when you transcode a codec like AVCHD or XDCamEX, to something like DNxHD or ProRes, you'll need to use a higher rate, maybe 115 at 1080p29.97, in order to achieve the same level of quality.  The file sizes will be much larger than the original, but playback and editing will be drastically faster than trying to edit raw media.

    But again - if you just want to use a low-resolution proxy to edit from, to save space as you edit, especially if you have massive amounts of raw media, you can, as BarkinMadd said, use something like DNxHD36, or even something like DNxHR-LB in 1/4 or 1/16 proxy mode, to get better performance, while sacrificing quality, and then relink the sequence to your originals later on.

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  • Thu, Sep 27 2018 6:19 PM In reply to

    • Lukas Boeck
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    Re: Import MP4

    At the same time i think that transcoding to say XDCAM 50 will work for editing as well as export.

    I'll eat my hat if you can really tell the difference coming from 8 bit 1.2Mbit mp4.

    you can try transcodig and see for yourself if you can spot the difference.

    this will probably save you some time if you have reviews.

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