Latest post Mon, Mar 16 2020 5:14 PM by nigelpedwards. 8 replies.
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  • Fri, Mar 13 2020 6:22 PM

    Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    I've been using Media Composer for a long time but I've never been happy that I'm doing the best thing when it comes to mixing down footage, so I'm hoping someone will be able to help me understand this better.

    I usually film using Sony cameras set to record XAVC HD 1080p at 50fps, which records MXF files. I find I can happily link to these files and edit (no need to mixdown at that stage), but before outputting a QT Ref file for Sorrenson Squeeze it's necessary to mixdown the final edit in the sequence.  Productions are typically for online use, but I still want to be sure that I'm getting good quality.

    So, I select Mixdown > Video and the dialogue box has a drop-down for "Resolution".

    Now, this confuses me straightaway as, surely, the resolution is full HD with 1920×1080 pixels - this setting is not going to decrease the video resolution?

    The default is "DNxHD 75" with other selections for "DNxHD 165", "DNxHD 240", "DNxHD 365" and "DNxHD 365 X".

    Should I just stick with the default of DNxHD 75?  There's a significant difference in disk space between the settings, for example for the 1 minute sequence in my timeline at present:

    DNxHD 75: 560MB

    DNxHD 165: 1242MB

    DNxHD 240: 1802MB

    DNxHD 365: 2728MB (the same for DNxHD 365 X)

    There are a number of other non-DNxHD options available too (I'm not sure if they'd all work with Squeeze) with the final DNxUncompressed in the list producing a whopping file of nearly 50GB.

    I have tended to use DNxHD 165 but I'm wondering if I'm actually wasting disk space - would DNxHD 75 actually be fine?

    If someone could explain this to me or point me to an explanation it would be most appreciated.

  • Fri, Mar 13 2020 9:08 PM In reply to

    • jef
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    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    Two part answer.

    First - what are you making in Sorenson?  That will have a big impact on the answer.

    Second - I would not do a mixdown / QT Ref.  I would do a MXF OP1a export to whatever dnx format makes sense based on your answer to the first question.  This will give a complete - REAL - file at what should only be slight longer than the mixdown.  This file can have many other uses beyond feeding Sorenson.  These render just as fast a mixdown.  All that is different is it adding audio files and writing externally from the Avid media management world.

    Just my opinion.  I quit using QT refs a long time ago.

    Jef

    EDIT: I do realize that this might not work with Sorenson, but I would definitely try.  And as to the first question - I would not make an uncompressed file if the goal were an .mp4 presentation file.  Overkill.  How much overkill would come down to testing and what the person receiving the file could play without issue.

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  • Sat, Mar 14 2020 2:37 PM In reply to

    • dew
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    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    I had came across this video and I am now exporting this way as its a time saver when I need to make changes.

     

    https://www.youtube.com/watch?v=3Ylubek84Lw

  • Sat, Mar 14 2020 10:35 PM In reply to

    • Ken Lent
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    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    In this case, resolution is referring to degree of compression, and the DNxHD number is approximate megabits per second.

    I think 75 and 165 are both designed for offline editing, generally not suitable for your end product:

         DNx75 for 50p is probably comparable to DNx36 for 24p, way easier to play unrendered in editors but with lots of artifacts.

         DNX165 for 50p is probably comparable to DNx80 for 24p, which was and may still be thin-raster 1440x1080.

    So I would export as DNx240 or higher, depending on the quality of your original footage and your project's requirements.

    Note:  I could not find an explanation/definition online -- any Avid experts please feel free to corroborate or correct me!

    Ken

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  • Sun, Mar 15 2020 11:51 AM In reply to

    • Mercer
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    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    Unless you have specific delivery specs from a client broadcaster/producer, there is no fixed concept of a finishing resolution for online internet. But as a rule DNxHD is cassified in these terms:

    Anything above 120 (Pal 50i/25p) and 145 (NTSC 60i/30p) 4:2:2 would be considered a finishing resolution, but the codecs come in X (10bit) and 8 bit flavours, so that's maybe another consideration. I always finish for HD broadcast delivery in 185x for the UK. There is no 50p delivery requirements here, regardless of the originating format, but it would presumably be double the aforementioned bandwidths.

    For online I then derive a high quality, best compression method, H264. It is just as important for online to be aware of the difference in legal and safe colour gamuts, from terrestial broadcast.

     

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  • Mon, Mar 16 2020 4:26 PM In reply to

    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    jef:

    Two part answer.

    First - what are you making in Sorenson?  That will have a big impact on the answer.

    Second - I would not do a mixdown / QT Ref.  I would do a MXF OP1a export to whatever dnx format makes sense based on your answer to the first question.  This will give a complete - REAL - file at what should only be slight longer than the mixdown.  This file can have many other uses beyond feeding Sorenson.  These render just as fast a mixdown.  All that is different is it adding audio files and writing externally from the Avid media management world.

    Just my opinion.  I quit using QT refs a long time ago.

    Jef

    EDIT: I do realize that this might not work with Sorenson, but I would definitely try.  And as to the first question - I would not make an uncompressed file if the goal were an .mp4 presentation file.  Overkill.  How much overkill would come down to testing and what the person receiving the file could play without issue.

     

    Thanks very much for your reply Jef, very much appreciated.

    The answer to your first question is that in Sorenson I'd normally be using the "YouTube_1080p" preset within the "MPEG-4 (*.mp4)" category.

    Exporting to MXF OP1a sounds an encouraging approach, however having tried it I'm afraid Sorenson doesn't appear to work. Even though the MXF file happily plays using VLC Media Player, Sorenson only plays the sound, and when the preset was applied it created an MP4 file that also had no video.

    So it would seem that a different encoding application would be needed. Adobe Media Encoder is mentioned in Kevin P Mc's video that's linked to in Dew's reply, however I believe that's not available as a stand-alone application and would require purchase (or is it only rent?) of another Adobe product too.

    One other thing to observe is that, when exporting as MXF OP1a I'm still faced with choosing a "DNxHD nnn" setting (not called "resolution" here though, rather it's called "video compression", which reading Ken's reply seems is the more accurate label). Interestingly the lowest setting is DNxHD 165, there's no DNxHD 75 as there is for mixdown (which is perhaps a strong indicator that you should never use DNxHD 75 for something that's being exported for final encoding and delivery).

  • Mon, Mar 16 2020 4:36 PM In reply to

    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    dew:

    I had came across this video and I am now exporting this way as its a time saver when I need to make changes.

     

    https://www.youtube.com/watch?v=3Ylubek84Lw

    Thanks for your reply Dew, that's a useful video that explains using MXF OP1a for export very well, and it's interesting that you can use Insert Edit Export. I noticed that someone has commented on the video though to say that it's not possible to use it if the overall length of the video changes, which makes sense I suppose, and that it also doesn't work, they said, with stereo exports (which seems odd).

     

    The main problem for me though is that, as mentioned in my reply to Jef, Sorenson Squeeze doesn't seem to work for MXF OP1a.

    And Adobe Media Encoder, as mentioned in Kevin P Mc's video, is, I believe, not available as a stand-alone application and would require purchase (or is it only rent?) of another Adobe product too.

  • Mon, Mar 16 2020 4:53 PM In reply to

    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    Ken Lent:

    In this case, resolution is referring to degree of compression, and the DNxHD number is approximate megabits per second.

    I think 75 and 165 are both designed for offline editing, generally not suitable for your end product:

         DNx75 for 50p is probably comparable to DNx36 for 24p, way easier to play unrendered in editors but with lots of artifacts.

         DNX165 for 50p is probably comparable to DNx80 for 24p, which was and may still be thin-raster 1440x1080.

    So I would export as DNx240 or higher, depending on the quality of your original footage and your project's requirements.

    Note:  I could not find an explanation/definition online -- any Avid experts please feel free to corroborate or correct me!

    Ken

    Thanks for your reply Ken.  That makes a lot more sense, it seems to me that it's the wrong label on the DNxHD selection for mixdown, especially given I've now noticed that when exporting as MXF OP1a the DNxHD selection is not called "resolution", rather it's called "video compression".

    It sounds like I ought to be using DNxHD 240 anyway.

  • Mon, Mar 16 2020 5:14 PM In reply to

    Re: Which DNxHD resolution to choose when mixing down prior to exporting a QT Ref?

    Mercer:

    Unless you have specific delivery specs from a client broadcaster/producer, there is no fixed concept of a finishing resolution for online internet. But as a rule DNxHD is cassified in these terms:

    Anything above 120 (Pal 50i/25p) and 145 (NTSC 60i/30p) 4:2:2 would be considered a finishing resolution, but the codecs come in X (10bit) and 8 bit flavours, so that's maybe another consideration. I always finish for HD broadcast delivery in 185x for the UK. There is no 50p delivery requirements here, regardless of the originating format, but it would presumably be double the aforementioned bandwidths.

    For online I then derive a high quality, best compression method, H264. It is just as important for online to be aware of the difference in legal and safe colour gamuts, from terrestial broadcast.

     

    Thanks for your reply Mercer, that's useful information.  It sounds like I need to be using at least DNxHD 240 then.  There's no X version for this though, I'd have to go to 365 X.

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