theory 30 to 24p

P

Park Edwards

Veteran
I haven't done the math exactly, but this is a thought. I've thought about using mjpeg 30p for some action sequences and instead of having a render farm to get proper 24p I have a thought.

Import 30p file.
Export image sequence photojpeg/tif
Delete every 7th frame in your sequence.
Import image sequence
Export image sequence to 24p

?????

What do you think?
 
Would have that weird dropped frames stutter...because you're..you know...dropping frames. 60p-->24p in a timeline does that as well, but since it can use a more regular pattern it is less noticeable.
 
If you do not have to sync the audio then can't you simply render the 30P to 24p - though the resulting footage will be little longer in length. I think with the progressive footage it will give the same look as that of 24p shot natively because the end result will be 24 frames displayed in a second and there won't be any dropped frames.
 
Ben_B said:
Would have that weird dropped frames stutter...because you're..you know...dropping frames. 60p-->24p in a timeline does that as well, but since it can use a more regular pattern it is less noticeable.
Click to expand...

dropping frames, yes, but dropping the right frames every second could lead to better results. can you notice 1 frame being dropped? That's 41 miliseconds a frame. The human eye can't possibly see a single frame dropped every 291.2 miliseconds.
 
Only way to know is to try...

I might do this, but how do you do this?

Import image sequence
Export image sequence to 24p

I'm guessing I'd be able to delete the right frame in photoshop, then just save it and import it to my NLE then export it back to 24p?
 
It's not that you consciously notice all the dropped frames, it's all about motion and the rate of dropping.

If you have constant motion for 291ms and then a slight break or stutter, it's noticable because the constant motion lasts for comparatively long. Granted 41ms is not noticable but 291ms is.
 
Excellent way to put it, commanderspike. There are unfortunately only 2 options - stuttery footage or lengthened footage. For a 13 second clip that's more than 3 seconds additional - smooth, but very noticeable in the speed of a pan, etc. Of course, this assumes I know what I'm talking about -- tested it both ways, but that's not saying I did it 100% correctly. :smile:
 
Obviously lengthened footage would look *exactly* like 24p but would be slightly slow-mo and out of sync with audio :)
 
yabyum said:
Only way to know is to try...

I might do this, but how do you do this?

Import image sequence
Export image sequence to 24p

I'm guessing I'd be able to delete the right frame in photoshop, then just save it and import it to my NLE then export it back to 24p?
Click to expand...

yep, i'm gonna try, just waiting on a nikon mount.


the way i plan on doing it is to phsycially delete the 7th file in the image sequence folder then drop that image sequence into quicktime pro, like you would with a timelapse and export to 24p. who knows. might work, but i think it's going to be better than 3hours of render time just for 5mins of footage.
 
commanderspike said:
It's not that you consciously notice all the dropped frames, it's all about motion and the rate of dropping.

If you have constant motion for 291ms and then a slight break or stutter, it's noticable because the constant motion lasts for comparatively long. Granted 41ms is not noticable but 291ms is.
Click to expand...

right, it's 291ms with a 41ms drop, then 291ms 41ms drop. it's the 41ms drop i don't think is possible to pickup on. it's 41ms.
 
30p footage converted to PAL 25p might be ok: just delete every fifth frame. In 30 frames delete frame 5, 10, 15, 20, 25, 30. That's 4 continuous frames either side of every deleted frame -- would the stutter of the missing frames be visible at that frequency?
 
I feel like 25p--->24p wouldn't be that noticeable with a frame delete but 30p-->24p...yeah I think I would notice.

If we can easily notice the 60-->24p when it's done the same way, but I believe as like 2 on 1 off 1 on 1 off, etc, which I think would be more subtle than 6 on, one off, than of course this is noticeable.

Seriously, I think this would be noticeable.
 
Here's the test results, and here's the problem: it looks like silky smooth 30p. It's 24p technically, but everything on either side of the dropped frame (which I by the way found VERY noticeable, look at the stuff at the end as the car drives away) is completely smooth.

Credit to DPreview for original footage, I didn't have anything 30p to work from. I exported from QT as Image Sequence, deleted every 7th frame by hand in the Finder (went pretty fast for a clip this short and being able to do arithmetic...sure there is an easy way to automate it) reimported as a 23.97 fps image sequence, and exported to mp4.

http://people.ucsc.edu/~bbunch/5D 30p to 24p Image Sequence Test.mp4
 
James Cameron tried a similar method to shorten the running time of terminator 2 and it looked horribly distracting. So simply removing the frames without the proper interpretation will look funky. If you have fcp, you could conform the clips to 23.98 in cinema tools in a matter of seconds. Then you'd have all the frames still in the shot. Then to get the proper speed you would just have to speed it up on the timeline or through compressor. People do this with 5d2 footage all the time. Can be issues with artifacts though, but it's an option.
 
it was panning that was distracting, otherwise, looked good. the goal here was to eliminate the 3hour render time needed to get 30p - 24p. i think i'm gonna mess around with it, see what i can do. thanks for everyones thoughts
 
That's why I mention cinema tools. Takes only seconds to conform to 23.98. But I guess you're using something other than fcp.
 
Did you not notice that aside from the frame drops it looks NOTHING like 24p?

Sure, it will conform in your 24p timeline to your other stuff, but it WILL NOT LOOK like 24p...this stuff looks like 30p! It's smooth! It just happens to drop a frame (which also looks like crap) regularly.
 
When I convert to 24p from 30p in Voltaic it only takes a very short time to do, but the end result stutters. As well it might, because of the dropped frames.

What about blending frames together instead? Might introduce a bit of motion blur but the frame rate versus actually camera movement would at least be constant and not have any irregular gaps.

Try slowing down footage in FCP by 50%, and enable frame blending.

Then render the sequence, export it, import it back into FCP & speed it up by 50%. Now you will have 30p but with frame blending. Then export this and convert it to 24p or 25p with Voltaic. See what it looks like. Can the eye be tricked this much?
 
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