VideoHelp Forum
+ Reply to Thread
Results 1 to 15 of 15
Thread
  1. Hi forum. Is there any setting in AviDemux to change just VFR (Variable Frame Rate) for output video. Source video is 60fps VBR (video frame) and I want to reduce it to 30 VFR FPS. I didn't see any option as VBR in filters. There is "Change FPS" and "Resample FPS" in "Filters" but it's CFR.

    Source video: HD MP4 (60 VBR FPS)
    Destination video: HD MP4 (30 VBR FPS)
    Quote Quote  
  2. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    VBR is Variable Bitrate. Not Variable Frame Rate


    So a resample FPS might work for you.


    But why even consider the change ?
    Quote Quote  
  3. You mean the video frame rate is CBR? (I am not video editor power user). Can frame rate be variable while shooting or recording or converting a video?

    I always change FPS from 60 0r 30 to 23 to reduce file size, in this case by changing the FPS to 23 it would be a bit sluggish.
    Quote Quote  
  4. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    Establish what you have. If not sure then send a mediainfo (text mode) report to this topic.


    CBR = Constant Bit Rate
    VBR = Variable Bit Rate
    CFR = Constant Frame Rate
    VFR = Variable Frame Rate


    Typically you will see Variable Bit Rate + Constant Frame Rate for the same video. Variable Frame Rate is less common. If you do have Variable Frame Rate then it will be more tricky to resample or change. It would inevitably require avisynth to do it and they are many on here more adept in that than myself.
    Quote Quote  
  5. Thanks. I did know CBR and VBR also ABR (I am better in audio than video! the last one is Adaptive Bit Rate). I didn't know it is not possible to change the frame rate to variable mode in AviDemux output. Thanks for your guide.

    I would give up because I don't know how it works (AviSynth) and the video I am trying to change its frame rate is the only one which is VBR.
    Quote Quote  
  6. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    You are still not being clear as to what you actually have. You write VFR but then say VBR.


    Allow me to make another suggestion. Within avidemux use the A/B markers to mark a short, say, 20 secs sample of the video. Use 'copy' for video and audio output and mp4 muxer for the output format. Save the video and upload it as an attachment to your next reply.


    I will then take a closer look at the sample.
    Quote Quote  
  7. I said the video bitrate is variable as its frame rate both of them are variable (Frame Rate and Video Bitrate = Variable).
    You can check it out (SS and video below):

    Image
    [Attachment 61782 - Click to enlarge]


    https://mega.nz/file/YkoFRAaD#YcgFJHSEu84zMNUzgz-9xM7EtmCNPalY42x002dIEuo

    As you know (better than me) videos with less motion or with more static frame contents, like part 2 of this video section which is showing an app UI and just have a little motion in centre of the frame (Aaron is designing a sticker on Adobe Illustrator) have better compression ratio. I think VBR and VFR would be better for these situations instead of constant rate for frame rate and video bit rate.

    I have changed its VFR to 23, all things are good for me but the Aaron parts (person frames) are sluggish and is like slow motion. I want to change the VFR to variable (from CFR 60 to VFR 60) then anytime Aaron (person of frame with lot motion) appears the frame rate would be maximum and when the static part of video are appear frame rate would be less and video size decreases.

    OS: Win 11 x64 (latest official build)
    Player: VLC (MPC for getting media info)
    Converter (or Demuxer): AviDemux (latest build portable)
    Quote Quote  
  8. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    Thank you for the sample. You could really, as requested, simply sent this as an attachment to the post and not relied on an external source.


    The 'interesting' thing is that if you indeed followed my instructions your VFR source has now become a CFR file. Even the bitrate has changed.


    So, maybe, that is the way to proceed with the whole clip. Follow the instructions as before but without the A/B markers and create a CFR 'copy'.


    I will now spend a few minutes before bed-time( and the last glass of wine) and resample the 59.94 file to 29.97. I do not think one should consider 23.976/24 fps if this is a video, not film, source.


    Watch this space !!!
    Quote Quote  
  9. Member Cornucopia's Avatar
    Join Date
    Oct 2001
    Location
    Deep in the Heart of Texas
    Search PM
    To be clear, video size has NOTHING to do with framerate. Filesize = bitrate * running time. Your runtime with that same clip (unedited) does not change so the only change in size is due to the change in bitrate. EVER.

    It might seem that changing framerates would give you improvement in bitrate allocation, but that is rarely the case, especially in this modern world full of interframe capable codecs. They already do an excellent job of allocating bits to faster motion when needed (assuming you are using VBR, ABR, CQ, CRF...).

    You are doing yourself a disservice changing the framerate to VFR, and probably even when lowering the CFR. VFR comes with increased compatibility issues - especially if you ever intend to subsequently edit.
    As I have stated before, IMO, the only good use for VFR (and this is also with reservation) is in camera capture (usually phone) to optimize light exposure.


    Scott
    Quote Quote  
  10. Member Cornucopia's Avatar
    Join Date
    Oct 2001
    Location
    Deep in the Heart of Texas
    Search PM
    Note also that your seemingly VFR clip is really CFR, it is just that its framerate metadata is being mangled by that particular coding library.

    I mean, come on... Average 59.94, High 59.96, Low 59.92? Variability of 0.02fps. That just means that it is having difficulty tracking the actual CFR of 59.94 using the chosen timebase (which is common in many mp4 libraries).


    Scott
    Quote Quote  
  11. Member DB83's Avatar
    Join Date
    Jul 2007
    Location
    United Kingdom
    Search Comp PM
    I'm glad that Scott has interjected in to this discussion since he knows more about the 'peculiarities' of this than I will ever know.


    That I did manage to resample your '59.94' vid back to 29.97 is somewhat inconsequential since avidemux refused to alter the CRF >> Constant Rate Factor << from 26. That actually resulted in a larger file than I started with since the bitrate was bigger >> Note the formulae quoted <<. And to confound the issue the resultant file was quoted as VFR.


    But for the purposes of reference, here is the resampled video.
    Image Attached Files
    Quote Quote  
  12. Originally Posted by Cornucopia View Post
    Note also that your seemingly VFR clip is really CFR, it is just that its framerate metadata is being mangled by that particular coding library.

    I mean, come on... Average 59.94, High 59.96, Low 59.92? Variability of 0.02fps. That just means that it is having difficulty tracking the actual CFR of 59.94 using the chosen timebase (which is common in many mp4 libraries).


    Scott
    O0o0o0h!!!...
    Many thanks for your prefect explanation. I couldn't believe that the frame rate changing can not change the file size (before your explanation). I was wasting my time (!) for just 0.2-0.3 frame drops! Most of my videos are tutorials like this (about graphics and …, that somebody time to time for a bit of the time appears on video and most of videos are focused on the app UI which is static part of frame) and frames have more static data than dynamic, then I use my 2-MB per minute rule (I have found out it by trial and error in AviDemux). I add main video (like a 30-minute video with about 400-500 MB) in AviDemux, then in "Rate Control" section change the option to "Average Bitrate (Two Pass)" to 400-500 kbit/s and change audio to "ACC (FDK)" 80, it works great for me and reduce the video size to 55-65 MB. The difference is very little! (because as I said before most frames have static data and compression would be more optimized for this situation).
    Quote Quote  
  13. Originally Posted by DB83 View Post
    I'm glad that Scott has interjected in to this discussion since he knows more about the 'peculiarities' of this than I will ever know.


    That I did manage to resample your '59.94' vid back to 29.97 is somewhat inconsequential since avidemux refused to alter the CRF >> Constant Rate Factor << from 26. That actually resulted in a larger file than I started with since the bitrate was bigger >> Note the formulae quoted <<. And to confound the issue the resultant file was quoted as VFR.


    But for the purposes of reference, here is the resampled video.
    Thanks for your time (testing my video). Yes! the size increased! As Scott said it is just time wasting (to change frame rate), this video was the only one (in my collection) with VFR. I was watching it and I noticed "Aaron" (the tutor person in video) motions are more smooth and I checked the file info with MPC and noticed the bitrate is 60 (59.9) and is also variable (all my videos are 23-29 fps CBR) and decided to change it to my routine 23 fps but as VFR.
    Quote Quote  
  14. Originally Posted by Cornucopia View Post
    Note also that your seemingly VFR clip is really CFR, it is just that its framerate metadata is being mangled by that particular coding library.

    I mean, come on... Average 59.94, High 59.96, Low 59.92? Variability of 0.02fps. That just means that it is having difficulty tracking the actual CFR of 59.94 using the chosen timebase (which is common in many mp4 libraries).


    Scott
    Avidemux calculates counts for each Frame duration ("Histogram map" entry in the application log).
    Rounding can cause videos to be detected as VFR when they are in fact CFR.
    Avidemux will enforce CFR on loading such videos, and in this case the resampleFps filter is not needed to obtain the corresponding CFR output.
    Quote Quote  
  15. Originally Posted by DB83 View Post
    That I did manage to resample your '59.94' vid back to 29.97
    That video was apparently shot on film at 24 fps. Your 30 decimation gives a duplicate frame every 5th frame. Decimating to 24p would give smoother playback. And x264 is frame rate aware -- encoding at a lower frame rate will not reduce the average bitrate by much.
    Quote Quote  



Similar Threads

Visit our sponsor! Try DVDFab and backup Blu-rays!