Converting 50p to 25p without simply dropping frames

[Dave2ic]

I am using a Sony RX100M2 for video at 50p 28Mbps.

I want to convert some clips to 25p, but the methods I've been looking at seem to just drop every second frame, which seems to me a rather crude way of doing is as it's simply throwing away half your data. Also, the optimum shutter speed for 50p is 1/100 sec, so if you're discarding every second frame the resulting video at 25p won't look very smooth in panning.


Is there a way to convert 50p to 25p that makes use of all the data/frames to ensure smooth and high quality playback?

[racer-x]

Sure....................but it will then play at 50% of original speed.

[poisondeathray]

Not really

There are pros/cons to each method you choose. You simply cannot reduce 1/2 the frames without losing something

Some options are

1) straight decimation , but add motion blur (e.g. mvtools, mflowblur...)

2) some combination of frame blending

e.g.
merge(selectodd, selecteven)

[manono]

You could blend the frames, but you won't like the result.

Using AviSynth's QTGMC you can add some motion blur to smooth those pans. It's about the best way I know to do it.

Something like:

SelectEven()
QTGMC( Preset="Slower", FPSDivisor=2, ShutterBlur=1, ShutterAngleSrc=30, ShutterAngleOut=180 )

should do it. The settings are adjustable. From the included doc:

Single-rate output may look a little stuttery, depending on how the source was filmed/created. Adding motion blur to each frame can help with this, smoothing the feel of the slower rate playback. This is done by setting ShutterBlur to 1,2 or 3, then specifying the shutter angle that you wish the output to simulate. However, as there may be some motion blur already in the source you also need to specify/estimate the shutter angle used in the source. Shutter angles range from 0 to 360, with 0 being perfectly sharp and 360 being fully blurred from one frame to next (artificial output shutter angles > 360 are supported to a very limited degree).

Edit: A little late. This method is similar to pdr's option 1.

[racer-x]

Dang.......3 posts within 3 seconds, that's got to be a record.

[manono]

Hehe, 3 minutes, I think.

[Dave2ic]

Wow - thanks for all the prompt replies!

The reason I thought I'd shoot 50p is because in bright light it's not possible to maintain a slow enough shutter speed (1/50 sec) for 25p video on my RX100M2, as I can't attach a Neutral Density Filter. So I thought it would look a lot smoother using 50p, even if the shutter speed got very high.


However, if half the frames are being discarded to convert back to 25p, I'm probably worse off than shooting 25p at 24 Mbps. 50p is 28 Mbps, so discarding half the frames would leave me with 25p at 14 Mbps - and to make matters worse the frame rate will still be too high so panning will look stuttery. Is my thinking correct here?


Is another way to approach this to shoot 25p at 24 Mbps and add motion blur in post? If so, what's the best way to do this?


Or is there no real solution other than to get a filter adapter for my RX100M2 (like the Magfilter) and use an ND8 filter when I'm in sunlight to keep to shutter speed down?


Thanks for all the advice.

[poisondeathray]

However, if half the frames are being discarded to convert back to 25p, I'm probably worse off than shooting 25p at 24 Mbps. 50p is 28 Mbps, so discarding half the frames would leave me with 25p at 14 Mbps - and to make matters worse the frame rate will still be too high so panning will look stuttery. Is my thinking correct here?

In terms of bitrate - not exactly; because not all frames are allocated the same proportion of bitrate; and the GOP size is usually doubled for 50p shooting (resulting in better efficiency) - but the general idea is correct 25p @ 24Mbps would probably look better due to higher average bitrate per frame

In terms of high framerates - If you pan from A to B over 10 seconds, it's the same amount of "stutter" or choppiness cadence wise (disregarding motion blur) whether or not you shoot native 25p vs 50p and take every 2nd frame

Is another way to approach this to shoot 25p at 24 Mbps and add motion blur in post? If so, what's the best way to do this?

Or is there no real solution other than to get a filter adapter for my RX100M2 (like the Magfilter) and use an ND8 filter when I'm in sunlight to keep to shutter speed down?

Motion blur in post is always a gamble. Sometimes it works great, but some situations can be a nightmare. It's really content and situation specific. But if you can , real shutter blur is always better than synthetic

Overall, for avisynth I would say most of the time QTGMC produces slightly better results than mflowblur. I would say 3rd party motion blur RE:Vision FX ReelSmart Motion Blur (for After Effects, but they might have versions for some NLE's) is slightly better

[racer-x]

It really boils down to what your final format will be. If you will export to Blu-Ray, then 50p is supported at 1280x720 anyway. Personally I would shoot 50p as more options are available to you.

Have you tried shooting in Aperture Priority and selecting a wide open aperture. This will require constant focus adjustments. Also you need to slow your pans (or eliminate them) and use a good tripod.

[racer-x]

.........Ooops just noticed this is a compact still camera (similar to my Sony HX9V) that also shoots video. Disregard my last post and maybe frame blur will be your best option.

[Dave2ic]

It really boils down to what your final format will be. If you will export to Blu-Ray, then 50p is supported at 1280x720 anyway. Personally I would shoot 50p as more options are available to you.

I don't really have any need for 50p, but I would like to ensure my 25p video doesn't get jerky by letting the shutter speed get too high in bright sunlight. I thought the additional frame data from using 50p would help with this if I convert back to 25p, but it seems this is not the case.
If I want 25p I should shot 25p.

Have you tried shooting in Aperture Priority and selecting a wide open aperture. This will require constant focus adjustments. Also you need to slow your pans (or eliminate them) and use a good tripod.

But aperture wide open only increases shutter speed as it let's more light in. I need to stop down to decrease shutter speed, but even then I need another 2-3 stops to get as skew as 1/50 sec for 25p.


So I don't think there's anything else I can do but to get myself a thread adapter with an ND4 or ND8 for my RX100M2.

[vhelp]

post a small (moving) sample to give people something to try possible ideas.

[racer-x]

The idea of shooting with a wide open aperture implies getting a shallow DOF. Since this a compact digital camera, that throws that logic out the window, hence the reason I said to disregard that post.................

I incorrectly assumed that this was a decent quality video camera................sorry my bad.

[glenpinn]

I use VideoReDo Professional, i shoot 1080/50p @ 28Mbps and on one occasion just after Xmas i filmed the finish of an ocean yacht race where i live in australia, and the finished video was 45 minutes, and 9gb in size, which would take me at least 25 hours to upload, so i dropped it to 1080/25p, which dropped it to 4.5gb, so the upload time only took around 12 hours to upload.

By doing this, VRD removes half the frames, and the software does something to extend the left frames to fill the void, and altho my video is still beautiful quality, in panning scenes, or where there is fast moving objects moving past the camera (like a car) the video is a bit jerky, but i will never shoot video in anything other than 50p, especially when i am in roaming mode and using my custom hand held rig.

On a tripod with a nice fluid head, with just slow panning, you can do 25p video, or in my case i can shoot 50p then drop it to 25p and not suffer any, or at least very mild jerkiness.

Since that video was uploaded, i decided to try uploading a short sample 1080/50p mp4 file, and watched it in my firefox browser, only to find the video jerky, then i found out firefox will not let you play video in 50p, only 25p, so i tried it with Chrome and they actually let you select the 50p video and it plays it at 50p, so i will be moving to Chrome just for this feature.

I have now added several new videos to my youtube channel, with about 100 more to upload in the next month or 2, but rather than waste time uploading the 1080/50p files (again some will take too long) i converted the videos to 720/50p mp4 @ 13Mbps (thats what VRD uses) so my files are still in 50p but the files are about 45% smaller in size, halving the upload time, and in Chrome they look great.

1080/25p Video
https://www.youtube.com/watch?v=qH_H2meHFHA

720/50p Video
https://www.youtube.com/watch?v=WBonaYlbiqg

[smrpix]

The Sony RX100M2 is a pretty sophisticated camera with a lot of available settings. You can turn the iso as low as 100 and set the shutter speed as low as 8 seconds in aperture priority. You should be able to find some settings that work for you. Or add an ND.

[newpball]

I am using a Sony RX100M2 for video at 50p 28Mbps.

I want to convert some clips to 25p, but the methods I've been looking at seem to just drop every second frame, which seems to me a rather crude way of doing is as it's simply throwing away half your data.

Think about what you are asking.

Say you have a film script of 1000 pages, how can you reduce it to 500 pages without losing half your data?

Right, you can't!

[glenpinn]

I am using a Sony RX100M2 for video at 50p 28Mbps.

I want to convert some clips to 25p, but the methods I've been looking at seem to just drop every second frame, which seems to me a rather crude way of doing is as it's simply throwing away half your data.

Think about what you are asking.

Say you have a film script of 1000 pages, how can you reduce it to 500 pages without losing half your data?

Right, you can't!

Lose half the Data, so the software has to manipulate the used frames to fill the void, retaining the original length of the video and the Audio track.

[Cornucopia]

Not the best option, but you could always INTERLACE (aka convert from 50p to 25i) - ¡Qué Horror!. It would drop data but would keep the general motion smoothness.

Depends on what your final target platform & display uses...

Scott

[glenpinn]

Not the best option, but you could always INTERLACE (aka convert from 50p to 25i) - ¡Qué Horror!. It would drop data but would keep the general motion smoothness.

Depends on what your final target platform & display uses...

Scott

I wanted to convert a 1080/50p video to an mpeg2 p/s and usually VRD just drops the resolution to Standard Def and keeps the video at 25p, making it jerky in the panning scenes, so i did a conversion to 25i using TMPGE and the jerkiness goes away, but the video looks horrible, so if i ever need to output to dvd for someone, i just keep it at 25p.

[TorBru]

FFMpeg's tblend filter should give you the possibility to take frame pairs and blend them into one frame. Doing this in combination with a lowerage of fps should give you 25p without loosing any image data. The result of this is unknown, I've never tried it. A command could look something like:

ffmpeg -i "your_50p_file" -filter_complex "[0:v]tblend=all_mode=average[blended];[blended]fps=25" -c:v h264 -c:a copy -crf 20 "your_25p_file"

I've not testet the command and I'm not sure it produces the wanted result - but if it does it will make a "motion blur" effekt by frame combination

[newpball]

FFMpeg's tblend filter should give you the possibility to take frame pairs and blend them into one frame. Doing this in combination with a lowerage of fps should give you 25p without loosing any image data.

Surely you must be joking.

I got this art book with one hundred paintings, but it is too thick to my liking. No problem, I blend every two pages. Finally I can enjoy 50 blended pages without losing any image date. Yeah sure!

[LMotlow]

Not the best option, but you could always INTERLACE (aka convert from 50p to 25i) - ¡Qué Horror!. It would drop data but would keep the general motion smoothness.

Depends on what your final target platform & display uses...

Scott

I wanted to convert a 1080/50p video to an mpeg2 p/s and usually VRD just drops the resolution to Standard Def and keeps the video at 25p, making it jerky in the panning scenes, so i did a conversion to 25i using TMPGE and the jerkiness goes away, but the video looks horrible, so if i ever need to output to dvd for someone, i just keep it at 25p.

Of course it looks horrible. HD downsized to SD always looks that way unless some very specific and tricky downsizing procedures are used. DVD is almost always interlaced, telecined, or encoded as interlaced. Many encoders won't even allow encoding DVD as 25p without issuing warnings, or will enforce encoding progressive as interlaced, and some authoring programs won't accept 25p DVD. Even BluRay for SD at 25p is out of spec.

If you do this for others, I hope they don't pay you for it.

Blended frames? OMG, how many threads are in these forums from people who are desperate to repair blended-frame videos? I'm with newpball on this: very bad idea.

The creativity people use to f.u. digital video is unlimited. Some of it even makes VHS look good.

[TorBru]

Surely you must be joking.

I got this art book with one hundred paintings, but it is too thick to my liking. No problem, I blend every two pages. Finally I can enjoy 50 blended pages without losing any image date. Yeah sure!

LOL! If you look at your art book with 50 pages per second I think they would blend 'n blur anyway

Really; It could somehow be mended to work since it is not 50 different images pr sec 50 frames of flowing motion. I've just tried my command from above and it does not cut away the frames as intended. Instead it gives you a 25p blurry something. But a bit of trial and error often leads to success

[newpball]

But a bit of trial and error often leads to success

The success is easy here: don't change the framerate and view it on equipment that can handle it.

And yes if your cousin's second removed great grandmother (second removed) only has this:



Then too bad, shit happens!
Have her come over enjoying cookies and tea while watching it on a 21th century screen!

[LMotlow]

Uh, newpball, that's not what we're talking about. Anyway, the video is HD.

[_Al_]

glenpinn is talking about web viewing trying to have smooth playback, so advice about longer shutter speeds or using ND filter are valid if there is planning for the future, but to bring this old TV picture and old stuff is really not necessary ...

[newpball]

glenpinn is talking about web viewing trying to have smooth playback, so advice about longer shutter speeds or using ND filter are valid if there is planning for the future, but to bring this old TV picture and old stuff is really not necessary ...

Youtube supports 50p/60p for some time now.

[smrpix]

OP has never stated his ultimate viewing method other than to say he wants 25p. What he also says he wants longer exposure times to smooth out his pans with some motion blur. Let's re-focus people.

So, anybody know of some software that can create convincing, proportional, directional motion blur?

[poisondeathray]

The OP's last reply was over a year ago

[smrpix]

Yikes!