Handbrake: Detelecine + Deinterlace Bob introduces video flickering

[Nomis101]

Description of the problem

If a video is converted with Detelecine plus Deinterlace method Bob, it can introduce a flickering to the video.

I have a sample uploaded here: http://polysom.verilite.de/tmp/Archiv.zip
The file "Sample Original.mov" is the original file and "Sample Converted.m4v" the flickering sample after conversion.

Steps:

1. Open "Sample Original.mov" in HB
2. Select any preset (I used "Fast 1080p30").
3. Go to the Filters Tab and select "Detelecine: Default" AND "Deinterlace: Decomb - EEDI2 Bob" (or just Bob).
4. Convert the movie and inspect the result. You will see a flickering in the resulting movie.

HandBrake version (e.g., 1.0.0)

Version 20191107135059-e9b2536-master (2019110701)

Operating system and version (e.g., Ubuntu 18.04 LTS, macOS 10.14 Mojave, Windows 10 1809)

macOS 10.14 Mojave

[bradleysepos]

By flicker it seems you mean frame rate stuttering. Unfortunately, Detelecine does not work for PAL sources. I'm not sure what the interaction with bob is.

[jstebbins]

If the source is PAL, there's nothing to do here. Detelecine and PAL are simply incompatible.

[Nomis101]

By flicker it seems you mean frame rate stuttering. Unfortunately, Detelecine does not work for PAL sources. I'm not sure what the interaction with bob is.

I'm not sure, what correct technical term this flicker is, could be frame rate stuttering. Neither ffmpeg nor mediainfo does give me any hint, that this source could be PAL. There is no issue with Detelecine or Deinterlace alone or with anything other than Bob. It only happens with the combination Detelecine + Deinterlace + Bob.

If the source is PAL, there's nothing to do here. Detelecine and PAL are simply incompatible.

Good to know. There is no hint for that. Not in the tooltip or somewhere else in the GUI. Why not deactivating Detelecine, if the source is PAL, if it is known to be incompatible?

[bradleysepos]

To be more specific, it's incompatible with PAL frame rates, or only compatible with NTSC 24p to 30p telecine. With variable frame rates these days, it's almost impossible to reliably make a decision here without manual intervention, but we can and should make this more clear for the user.

[jstebbins]

To be more specific about the PAL issue. Telecine is a specific pattern of interleaved frames that results in a more pleasing motion smoothness when converting 24fps film to 30fps. The detelecine filter detects this pattern and non-destructively reverses it to recover the original 24fps frames. PAL doesn't use such a pattern to convert 24fps to 25fps. With PAL, the detelecine filter seems more prone to incorrectly locking to a false pattern and applying the reversal process which causes the jerkiness you see.

[Nomis101]

Ah, interesting. Thank you both for the insight. :-)

[luziferius]

And detelecine (or IVTC, _Inverse Telecine_) already converts an interlaced source into progressive frames, so further de-interlacing is redundant and may even degrade image quality. (Unless someone applies the telecine filter on 23,976 FPS interlaced material. But does that even exist?)

Should enabling detelecine automatically deactivate other de-interlacing methods?

[jstebbins]

Should enabling detelecine automatically deactivate other de-interlacing methods?

No

@luziferius detelecine only converts telecined frames to progressive. If it can't lock on to the telecine pattern, the filter leaves the frames interlaced. So if you have NTSC material which you are unsure whether it is hard telecine or plain vanilla interlaced, you can enable both filters and HandBrake will do the right thing. There are also cases of mixed content where the source material is a mixture of hard telecine, interlace, and progressive frames. Generally, if the source is NTSC, you can enable detelecine, interlaced detection, and deinterlace and HandBrake will do the right thing for each sequence.

[Nomis101]

What about adding a note to the detelecine tooltip, to make it more clear that its not working with PAL frame rates?

https://github.com/HandBrake/HandBrake/blob/31254efcc4e64db44f2404c850b9f76e23e7c36c/macosx/Base.lproj/HBFiltersViewController.xib#L49

https://github.com/HandBrake/HandBrake/blob/31254efcc4e64db44f2404c850b9f76e23e7c36c/win/CS/HandBrakeWPF/Properties/ResourcesTooltips.resx#L141

Something like "Not work for PAL sources" or "incompatible with PAL frame rates" or "only compatible with 24fps film" or something like this?

[bradleysepos]

Thought of that, though I think Detelecine (NTSC) might be more obvious.