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Prores 4444 vs Prores 422HQ

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  • CMC
    started a topic Prores 4444 vs Prores 422HQ

    Prores 4444 vs Prores 422HQ

    I've just noticed that when I export an identical clip from Mpeg Streamclip as proress 422HQ and then Prores 4444, the files sizes of both clips are exactly the same. Streamclip seams to be exporting Prores 4444 at 422HQ data rates. Has anyone else noticed this?

    CMC

  • CMC
    replied
    Thanks for the replies.

    The source footage is an RGB-10bit 1920x1080 25fps quicktime captured live, with a Kona 3 capture card set to Dual Link, off of a telecine chain playing 16mm stock footage.
    There is no alpha channel, we need prores 4444 as one of our delivery formats to keep the color information so that it can be used for grading, etc. Exporting via FCP and Quicktime pro both yield the expected data rate of around
    250 mbits/s (DVS Clipster also hits this mark) where as mpeg streamclip and compressor both stick to the 422HQ data rate of about 170 mbits/s. Prores has a variable bit rate so I understand that file size will change with the visual complexity of the footage.

    So, as is clear in the white paper, there are two reasons to use 4444; alpha channel preservation, and color detail preservation, for which we would expect a higher bitrate (see page 10 of the whitepaper). It seems that streamclip and compressor are only interested in the alpha channel capabilities of the codec...interesting. Indeed, I notice that compressor does not even call it's target option Prores 4444, rather "Apple Prores with Alpha", even though browsing the Inspector in the resulting quicktime reveals that it is at least technically a Prores 4444 file. It's a pity, because I could really use compressors batch rendering capabilities, not to mention the fact that it keeps the timecode track, unlike most other transcoding options.

    Thanks again

    CMC

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  • NoahKadner
    replied
    Yep exactly- you don't neccesarily see huge differences at those upper codec levels in ProRes- depending on the complexity/type of the source.

    Noah

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  • Zwick
    replied
    Yep, this question is rather meaningless without knowing what the source footage is. However, there is a significant difference in file size when you carry an Alpha channel. For more info read Apple's White Paper on ProRes. (Clicking this will download the PDF.)

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  • BenB
    replied
    Alpha channels don't take up much data at all, so yes, you'll get about the same size on both. Question is, does your original actually HAVE an alpha channel to start with. If not, there's no data to add in the 4444 encode. What codec was the original file?

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  • CMC
    replied
    Thought I'd reply to my own post to make it more relevant to this "compressor" forum. I just tried the same test with compressor, which I almost never use, and got the same result. Both the 422HQ and the 4444 have identical data rates. I think maybe that both applications (streamclip and compressor) have the 4444 option for it's alpha channel capability only and not the higher data rate that RGB media necessitates.

    Anyone...

    CMC

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