Quantcast Deinterlacing with QTGMC changes to 50p? - digitalFAQ Forum
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04-03-2021, 07:15 AM
chrisbati chrisbati is offline
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Hello,

I'm starting with deinterlacing with qtgmc.

I deinterlace material from PAL DV and Video8 PAL.
I use basic script:

Code:
AVISource("U:\Media a traiter\tbd3.avi")
AssumeTFF()
QTGMC(preset="slower", EdiThreads=3)
Prefetch(10)
My source files are PAL 25p interlaced.
In virtualdub2 i use streamcopy to keep the source file format, but doesn't seem to work.

When finished, I have PAL 50p and the bitrate change from 56 mbs to 332 mbs !
Is it normal that the framerate is doubled ?

Here are the information of the files:

Original file
Code:
Video
ID                                       : 0
Format                                   : HuffYUV
Format version                           : Version 2
Codec ID                                 : HFYU
Duration                                 : 12 min 56 s
Bit rate                                 : 56.1 Mb/s
Width                                    : 720 pixels
Height                                   : 576 pixels
Display aspect ratio                     : 5:4
Frame rate                               : 25.000 FPS
Standard                                 : PAL
Color space                              : YUV
Chroma subsampling                       : 4:2:2
Bit depth                                : 8 bits
Scan type                                : Interlaced
Bits/(Pixel*Frame)                       : 5.410
Stream size                              : 5.07 GiB (97%)
After script (not all the video, just an extract)
Code:
Video
ID                                       : 0
Format                                   : YUV
Codec ID                                 : YUY2
Codec ID/Info                            : YUV 4:2:2 as for UYVY but with different component ordering within the u_int32 macropixel
Duration                                 : 4 min 40 s
Bit rate                                 : 332 Mb/s
Width                                    : 720 pixels
Height                                   : 576 pixels
Display aspect ratio                     : 5:4
Frame rate                               : 50.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:2
Compression mode                         : Lossless
Bits/(Pixel*Frame)                       : 16.000
Stream size                              : 10.9 GiB (100%)
Thanks in advance for any help or advice.

Chrisbati
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  #2  
04-03-2021, 07:40 AM
lollo2 lollo2 is online now
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interlaced frames video, 25 frames (50 fields) per second (25 frames i)
Code:
frame1    frame2    frame3    frame4    frame5    frame6    frame7    frame8
A...........C..........E..........G................................................................(field 0) even lines
b...........d..........f...........h............................................................... (field 1) odd lines
QTGMC deinterlaced [frame count is doubled] --> (50 frames p)
Code:
frame1    frame2    frame3    frame4    frame5    frame6    frame7    frame8
A...........B'...........C..........D'........E.......F'.........G..........H'......................(field 0) even lines
a'...........b...........c'..........d.........e'.......f..........g'..........h......................(field 0) odd lines
x2 -> x2 = x4 data = ~x4 size
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  #3  
04-03-2021, 07:49 AM
latreche34 latreche34 is offline
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Yes QTGMC in the default setting doubles the frame rate but it uses complex math to achieve that it doesn't just repeat the fields. But when you encode to h.264 the size will go down, I personally get about 5-10 GB an hour files in 4:2:2 h.264 and 192 kbps stereo audio, Way better than DV and DVD in quality. And I keep the HuffYUV interlaced captures as master files not the de-interlaced ones.
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The following users thank latreche34 for this useful post: lordsmurf (04-03-2021)
  #4  
04-03-2021, 10:18 AM
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Don't use preset=slow. It blurs. The NR is too aggressive.
Do faster.
If anything looks odd, do medium.
If anything still odd, do manual switches, not a preset.

The file size of the output file it is indeed 2x when you retain all fields. But when compressing, it goes down. The primary compressor here is not actually bitrate, but the GOP. If you get 1.5x, you're fine. If you get 1.25x, you're aggressive. If you have 1:1, then you overcompressed.

Fields are 50% frames, but temporally offset. When you create frames from fields, data is duplicated. While you do get some movement frames, you also get a lot of outright duped frames. This is why deinterlacing back to 25fps/29.97fps is not "losing data". Not really. It's just not inventing new data. Both ways are fake, whether 50/59.94 or 25/29.97. Adding data has bad side effects at times. It's not a simple process. I've had to just dump even/odd fields before, due to either excessive work, or outright refusal to deinterlace well. Very often, it was a choice between 50/60 Yadif (some aliasing), or 25/30 QTGMC (no aliasing). Tough choices.

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