Latest post Wed, Mar 20 2019 9:41 AM by Dan_B. 10 replies.
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  • Wed, Feb 13 2019 4:27 PM

    Transcoding frame rates

    Hi,

    On my GH5 I film at 50fps. I have a project in MC set at a frame rate of 25fps.  When transcoding it asks whether to convert? So far I have said yes. As this is a direct multiple it should be Ok, so can I just transcode at the filmed rate (making slow-mo in edit easier)? What about weird ratios (filmed to edit project) - is it best to convert or to keep as original? (Technically, I am not certain if I have used the correct terminilogy phrasing this question.)

    DC

    Asus N55SF Notebook running Windows 10 Home Processor: Intel(R) Core (TM) i7-2670QM CPU @ 2.20GHz 2.20GHz Installed memory (RAM): 8.00 GB System type... [view my complete system specs]
  • Wed, Feb 13 2019 5:58 PM In reply to

    • Tom Pearson
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    Re: Transcoding frame rates

    As a given I always trans code to my frame rate in a native avid format

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  • Wed, Feb 13 2019 8:42 PM In reply to

    Re: Transcoding frame rates

    Hi Tom, thank you for coming back. Though please forgive me, I'm not sure I'm reading your response as the answer to the question. Can I transcode an original 50fps, keep it at this, and into a 25fps project? This, in theory at least, gives better options with a time warp speed reduction.

    DC

    Asus N55SF Notebook running Windows 10 Home Processor: Intel(R) Core (TM) i7-2670QM CPU @ 2.20GHz 2.20GHz Installed memory (RAM): 8.00 GB System type... [view my complete system specs]
  • Wed, Feb 13 2019 9:44 PM In reply to

    • gumbycat99
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    Re: Transcoding frame rates

    I usually transcode at the source files original frame rate. There are a couple of reasons for this.

    1. Slomo (this is what you're doing). If you transcode at the source 50fps then when you edit into the timeline Avid will add a motion adapter effect so that is plays on the 25fps timeline. If you open the motion effects editor then you can click 'Promote' to turn it into a full time-warp effect. Now you can halve the playback rate to make it a slomo using all the original frames. (If you had transcoced to 25fps then half the frames are thrown away and you can't get them back).

    2. Tweaking non-25fps footage to use for B-roll. If you get phone/dslr footage that has been shot at 30fps then transcode this at that original speed. Now go into the clips Source Settings and change the clips palyback framerate to 25fps. This means the clip will play at a slight slo-mo but without any frame-blending. I use this a lot for B-Roll that comes from odd sources as I find the slight slo-mo more acceptable than the frame-blending that happens when the 30fps is forced into a 25fps timeline.

    Hope this makes sense and helps.

    cheers

    Campbell

    8.5 on a mongrel PC, Win 7, QT7.5, Nvidia GTX 970, 16Gb RAM, SSD, NAS for raw media and a Macbook Pro [view my complete system specs]
  • Thu, Feb 14 2019 10:25 AM In reply to

    Re: Transcoding frame rates

    Hi Gumbycat (what a name!), interesting. Several things in response. 1. so overall I can transcode at any original frame rate, irrespective of the project’s frame rate? 2. if I transcode at 50fps, and not have it convert there and then  to 25fps, then effectively the MXF file will be twice as large? 3. If I transcode at 50fps, then placing this on a 25fps video track Avid does the work of ‘dropping’ alternate frames for purposes of playback and editing, while at the same actually keeping the ‘dropped’ frames in storage (for lack of a better term) so that in-edit slow-mo is smoothly facilitated? 4. Mobile phones record at 30fps (is this standard?) and if there is a dialogue then all this footage will play at slightly slower speed? 5. What, technically, is frame blending? Thank you, DC

     

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  • Thu, Feb 14 2019 9:30 PM In reply to

    • gumbycat99
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    Re: Transcoding frame rates

    Supermandan1:
    1. so overall I can transcode at any original frame rate, irrespective of the project’s frame rate?

    Yes! Awesome feature that came in a year or 2 ago. So now you can either a.Transcode everything to your delivery format at the beginning (which lots of people like to do to keep things simple during editing) or b. Transcode but keep the original frame rate and frame size so that you can have more options to manipulate things while editing.

    Supermandan1:
    2. if I transcode at 50fps, and not have it convert there and then  to 25fps, then effectively the MXF file will be twice as large?

    Haven't checked but I expect that this is the case as there are twice as many frames. You could transcode it both ways and then right-click on the clip in the bin and 'reveal source file' and check the file sizes.

    Supermandan1:
    3. If I transcode at 50fps, then placing this on a 25fps video track Avid does the work of ‘dropping’ alternate frames for purposes of playback and editing, while at the same actually keeping the ‘dropped’ frames in storage (for lack of a better term) so that in-edit slow-mo is smoothly facilitated?

    Yes exactly. Avid puts a 'motion adapter' effect on the clip which converts in real-time to 25fps. This means extra work for you computer which is one reason some people like to transcode to their delivery format at the beginning. You can select the method for the conversion by opening the Motion Effects Editor from the Tools menu and adjusting the settings. But basically in this scenario Avid will play back frames 1,3,5,7 etc but frames 2,4,6 etc are still thre in the clip, just not being displayed when you play back in your 25fps timeline.

    To 'retrieve' the extra frames for a slomo effect you can either Promote the motion adapter to full Timewarp and then adjust the speed, or change the playback rate in the Source Settings of the clip. (If you change the Source Settings then this sets the frame rate for every time you use the clip after that. If you've already put the clip in the timeline you may need to right-click on the sequence in the bin and choose Refresh->Motion adapters to update the sequence with the new source settings.

    Supermandan1:
    4. Mobile phones record at 30fps (is this standard?) and if there is a dialogue then all this footage will play at slightly slower speed?

    Seems to be the standard for phones to record at 30/29.97fps although this can be changed by some apps. I haven't tested what happens to audio if you change the source settings to a different rate, sorry. You may need to add a time-stretch effect to the audio manually?

    Supermandan1:
    5. What, technically, is frame blending?

    Frame blending is when extra frames for a slo-mo are created by dissolving between the existing frames. so if you have frames 1,2,3 and then slo-mo by 50% then you'll get extra frames 1b (which is a dissolve between 1 and 2) and 2b (which is a dissolve between 2 and 3) etc. Looks ok-ish on TV if you need it. There are other options such as duplicating frames or using Fluidmorph to create the extra frames. But nothing looks as good as if you actually have the extra frames from the original footage.

    Hope that all makes sense. Others may have better explanations than me if not or if I've got something wrong.

    cheers

    Campbell

    8.5 on a mongrel PC, Win 7, QT7.5, Nvidia GTX 970, 16Gb RAM, SSD, NAS for raw media and a Macbook Pro [view my complete system specs]
  • Sat, Feb 16 2019 11:12 AM In reply to

    Re: Transcoding frame rates

    Thank you, very helpful set of replies.  On a tangent, I did do a time lapse once - thoroughly manually - where I doubled-up every single frame on the timeline (1 frame playing over 2fps) and did a dissolve between each succeeding frame. The final effect was fabulous, though just lots and lots of work to get there.

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  • Sun, Mar 17 2019 6:19 PM In reply to

    Re: Transcoding frame rates

    Hi,

    Quickie update confirmation.  I have footage shot at 50fps, and a project set to 25fps.  Now ready to transcode, ticking "keep source's frame rate" and target video resolution changes to "DNxHR LB MXF".  Is this correct?

    DC

    Asus N55SF Notebook running Windows 10 Home Processor: Intel(R) Core (TM) i7-2670QM CPU @ 2.20GHz 2.20GHz Installed memory (RAM): 8.00 GB System type... [view my complete system specs]
  • Mon, Mar 18 2019 10:44 AM In reply to

    • Dan_B
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    Re: Transcoding frame rates

    Yes thats correct.

    If you require an offline codec which isn't on that list you need to transcode within a separte 50fps project an then copy the bins into your 25fps edit project.

    DNXHR LB is a decent offline codec - Its like a dynamic DNXHD36 - assuming you're working at HD at 50fps the bandwidth will be around 72Mbps.

     

  • Wed, Mar 20 2019 8:10 AM In reply to

    Re: Transcoding frame rates

    Hi Dan, thanks for getting back. This is all a bit on the tecchie for me, though always good to learn.  Can you elaborate a bit more on what you said?  Is the "dynamic" part of extra significance?

    D.

    Asus N55SF Notebook running Windows 10 Home Processor: Intel(R) Core (TM) i7-2670QM CPU @ 2.20GHz 2.20GHz Installed memory (RAM): 8.00 GB System type... [view my complete system specs]
  • Wed, Mar 20 2019 9:41 AM In reply to

    • Dan_B
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    Re: Transcoding frame rates

    Hi,

    no problem it can be a bit confusing at times.

    previous Avid codecs are named and grouped by their data rate / bit rate and are dependent on raster size & frame rate.

    for example DnxHD185 is 185 mbit/s and is HD 1920x1080, this format is available at 25 fps.

    the equivalent at 29.97 is DnxHD220 (220 mbit/s) because of a higher frame rate a higher bit rate is required to maintain the same level of quality - so the options change meaning the user is required to know what codecs match which rasters and frame rates.

    At 23.98/24 fps the user is offered DnxHD 175.

     

    in the case of the newer DnxHR codecs the bit rates are largely masked from the user.

    so for DnxHR HQ this will be roughly 185 mbit/s at 1920x1080 at 25 fps, when switching to UHD the same codec choice is available but Avid will scale up the bit rate as required.

     

    This has more info on the bit rates available for DnxHR and also the bit depths.

    http://avid.force.com/pkb/articles/en_US/White_Paper/DNxHR-Codec-Bandwidth-Specifications

     

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