Converting the Mini's 30fps video to 24fps

[RogerDH]

I've seen complaints in some Mini reviews about the lack of a 24fps mode. That may be added in the next firmware release, but one way to convert 30fps video to 24fps is to just slow it down to 80% of its original playback speed. The frame rate isn't directly specified in the MP4 files, but it is possible to change the "timescale" values that determines the effective playback frame rate that video viewers and editors will use. There's no need to re-encode the video stream itself, so there's no loss of quality.

I have several Mobius cameras, so I use the mSetup Windows utility to configure them. One of the functions that it has it to change the playback speed of an MP4 video file. I just tested it on a Mini video, and it works fine. (This method doesn't change the length of a sound track, but that's no problem for Mini videos since they don't have any.)

You can download mSetup here. Don't worry about the startup screen that wants to connect to a Mobius camera -- just click the Tools button, then under Special Functions, click the box for "Modify existing MP4 or MOV videos to increase or decrease playback speed." That will open a window where you can drag and drop one or more Mini video files. You can specify a different directory for the result files, or if you unset that checkbox, it will rename the original files to add .bak and write new files with the original names on the same directory. At the bottom, there is an option to change the playback speed by a specified factor, but the desired 0.8 isn't an option, so you need to click the box for "Allow manual edit" and change the 30000 value in the box to be 24000. Then click Modify, and you will have video files that your editor will think were shot at 24fps.

Edit: I have verified that this also works to change a 25fps video to 24fps using the same 24000 value.

 

[brett8883]

I've seen complaints in some Mini reviews about the lack of a 24fps mode. That may be added in the next firmware release, but one way to convert 30fps video to 24fps is to just slow it down to 80% of its original playback speed. The frame rate isn't directly specified in the MP4 files, but it is possible to change the "timescale" values that determines the effective playback frame rate that video viewers and editors will use. There's no need to re-encode the video stream itself, so there's no loss of quality.

I have several Mobius cameras, so I use the mSetup Windows utility to configure them. One of the functions that it has it to change the playback speed of an MP4 video file. I just tested it on a Mini video, and it works fine. (This method doesn't change the length of a sound track, but that's no problem for Mini videos since they don't have any.)

You can download mSetup here. Don't worry about the startup screen that wants to connect to a Mobius camera -- just click the Tools button, then under Special Functions, click the box for "Modify existing MP4 or MOV videos to increase or decrease playback speed." That will open a window where you can drag and drop one or more Mini video files. You can specify a different directory for the result files, or if you unset that checkbox, it will rename the original files to add .bak and write new files with the original names on the same directory. At the bottom, there is an option to change the playback speed by a specified factor, but the desired 0.8 isn't an option, so you need to click the box for "Allow manual edit" and change the 30000 value in the box to be 24000. Then click Modify, and you will have video files that your editor will think were shot at 24fps.

This will make the video longer and playback noticeably slower though right?

 

[RogerDH]

This will make the video longer and playback noticeably slower though right?

Yes, it will be at 80% of the original speed, which isn't necessarily noticeable for aerial video, and it actually helps in getting a smooth "cinematic" effect.

 

[Starving Artist]

Why not shoot in 25fps? Is that one frame that bothersome? If so, wouldn’t it still be less problematic to shoot in 25fps and then convert to 24fps by slowing the speed down slightly in the editing process?

 

[RogerDH]

Why not shoot in 25fps? Is that one frame that bothersome? If so, wouldn’t it still be less problematic to shoot in 25fps and then convert to 24fps by slowing the speed down slightly in the editing process?

Supposedly, it was bothersome enough for several reviewers to rate it as a negative for people doing 24fps projects -- it's not a problem I've ever had to deal with. In the video editor I use, Vegas Movie Studio, I can do the same 80% slowdown by specifying a 0.8 playback speed factor for a clip without actually modifying the MP4 file. If you're working with an editor that allows that, then a factor of 0.96 would "convert" 25fps to 24. I'm just suggesting a way to make the playback speed change directly in the MP4, so it should work for any editor. Anyway, if I were to do a 24fps project, I think I'd shoot at 30fps because I think the slowdown would enhance the "cinematic" smoothness of the video.

 

[RogerDH]

Why not shoot in 25fps? Is that one frame that bothersome? If so, wouldn’t it still be less problematic to shoot in 25fps and then convert to 24fps by slowing the speed down slightly in the editing process?

I have verified that this method also works to change a 25fps video to 24fps, using the same 24000 value. (The timescale value in those files is actually 25000 rather than 30000 as mSetup assumes, so setting it to 24000 does the trick.)

 

[brett8883]

25 to 24 with this method would be good!

 

[RogerDH]

25 to 24 with this method would be good!

Actually, with the Mini, it works better for 25-to-24 than it does for 30-to-24. Because of another rate attribute in the file, the Mini's "30fps" is actually 29.97, the old NTSC standard,, so setting the timescale to 24000 makes the effective frame rate 23.98 -- close but no cigar if your editor doesn't want to work with a file that isn't exactly 24fps. The 25-to-24 doesn''t have that problem because the original is actually 25fps, so the timescale setting of 24000 makes it exactly 24fps.