FFmpeg / QTGMC Ratio Error

[SirHaakon]

Hello friends,

New poster here. I am in the process of beginning to capture a mountain of old VHS tapes and trying to store in the best quality that I can for archival purposes. I am choosing to first capture the videos in their native form to preserve as much of the signal as possible before processing, and then later upscaling, color correcting, etc., to present them more appropriately for the web.

In my current process, I am capturing into to a PC using Blackmagic's Media Express software. This captures uncompressed 8-bit YUV video, which I understand is what FFmpeg / QTGMC needs for deinterlacing. I am using the package presented here:

https://forum.videohelp.com/threads/405720-FFmpeg-QTGMC-Easy%21

...as it is incredibly easy and I do not have a working knowledge of Avisynth (nor do I have the time to invest in learning that top to bottom at the present). Everything seems pretty straightforward, however I get an error message when running the package stating "[avisynth @ 0000012b01c9e2c0] SeparateFields: YUV420 height must be multiple of 4." The captured files are 720x486, so it makes sense that it's throwing the error.

I did a little bit of research on FFmpeg and found that you can crop videos by adding -filter:v "crop=720:480:0:0" to the command line (I do not care if I lose the bottom 6 lines... it's mostly VHS artifacting anyway), but this approach did not work. I don't want to re-encode the videos by cropping them in an NLE first, so I'm just wondering if there is an easy way to just have the program "ignore" the bottom 6 rows so I can output a QTGMC-compliant, 720x480 file.

Any assistance would be greatly appreciated.

Thank you in advance!

[davexnet]

What is your ffmpeg command line and what modification(s), did you make to the files in the package?

[SirHaakon]

Hello,

The command line is just the one provided in the package:

ffmpeg -i qtgmc.avs out.mp4

As mentioned, I did try adding -filter:v "crop=720:480:0:0," but I got the same error.

The only modifications I made to the qtgmc.avs file were adding

SetFilterMTMode("DEFAULT_MT_MODE", MT_MULTI_INSTANCE) to the top and

# Enable MT!
Prefetch(8)

to enable multithreading (per thread comments), as well as SelectEven() to halve the framerate that comes from the QTGMC doubling. Everything else is just completely as provided.

[davexnet]

You added "-filter:v "crop=720:480:0:0," where exactly?

[SirHaakon]

I have tried both ffmpeg -i -filter:v "crop=720:480:0:0" qtgmc.avs out.mp4 (which gives a general error) and ffmpeg -i qtgmc.avs -filter:v "crop=720:480:0:0" out.mp4 (which gives the same error "[avisynth @ 0000012b01c9e2c0] SeparateFields: YUV420 height must be multiple of 4.").

[jagabo]

Your source video doesn't have a mod4 height (486 maybe?). Crop it in AviSynth before calling QTGMC.

[SirHaakon]

Is that something which can be done with the FFmpeg-QTGMC Easy! package?

[jagabo]

You would have to add the Crop() to the AVS file it uses. Try adding Crop(0,0,720,480) just before QTGMC.

[SirHaakon]

Sweet, thank you very much.