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Old 04-24-2017, 03:33 PM   #11
nbwriter
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Default Tech Know-How: Dos And Donts Of Vid Processing

Dear Contributors,

Quote:
... I tried various routes including full screen frame capture from playback
Full screen capture will usually result in "jitter" due to the lag caused by your PC attempting to process every single frame of a movie (in RAM) and transfering it back onto your hard disk. Most movies run at 24 frames per second, so even with "4 cores" you're asking alot from your processors!

The way to avoid jitter is by using a good encoder in the first place... MPEG4 is very good on Windows 7, for example. I used to use XVID (but good old Microsoft doesnt like that encoder much) although you'll get a good "output file" with XVID for sure. You can also re-process header information in avi files, which will reduce "jitter" further.

Quote:
... What's the point of having 4-core computing power and not using it?
4 core is blisteringly fast, but unless you have a basic knowledge of file formats and optimization software, you could be "ice skating uphill" for most of the time.

Quote:
... The 520p sections of the material... don't look markedly inferior after processing on a 28" screen compared to the 720p...
Assuming you have a 1080p TV, 520p content will be passable, but cannot be considered HD (technically). The secret is to optimize 520p content or find a 720p source of the same content and still optimize, so you're then making best use of your TV resolution (whatever screen size you have).

Quote:
If you're interested ... I'll post an FF link to my results once I've sorted out the title timing.
I'm not sure what a "FF link" is, but yes, I've had an interest in video production since forever (more of an Art than a science, once you get into it). But alot of it is geeky, super-geeky, so grasping the basics of optimization first is the way forward.

Kind Regards NB
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Old 04-24-2017, 11:18 PM   #12
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Quote:
Originally Posted by nbwriter View Post
Dear Contributors,

Full screen capture will usually result in "jitter" due to the lag caused by your PC attempting to process every single frame of a movie (in RAM) and transferring it back onto your hard disk. Most movies run at 24 frames per second, so even with "4 cores" you're asking a lot from your processors!

The way to avoid jitter is by using a good encoder in the first place... MPEG4 is very good on Windows 7, for example. I used to use XVID (but good old Microsoft doesn't like that encoder much) although you'll get a good "output file" with XVID for sure. You can also re-process header information in avi files, which will reduce "jitter" further.
Well, as I stated originally, the screen capture attempt was a hopeful experiment to negate the jitter already occurring. While I like XviD (and ffsdhow) for both their open source philosophy and their general ease of use in playback applications, I tend to use the DivX 6 plugin in VirtualDub for re-coding as its native interface allows keyframe intervals to be set easily, That helps make subsequent editing more precise. And it's a universally supported codec by apps such as MPC and VLC and others.

And I'm intrigued by the suggestion of altering the file header information. Presumably that'd be via a hex editior?

Quote:
Originally Posted by nbwriter View Post
4 core is blisteringly fast, but unless you have a basic knowledge of file formats and optimization software, you could be "ice skating uphill" for most of the time.
Quad core certainly helps, providing the software used is able to optimise its availabilty, But as back-of-a-fag-packet calcs go, I estimated 25 fps, at 720x540 with 32 bit colour depth should still leave a whole heap of spare cycles on a 3.4 GHz processor, even for screen capture. And overnight on an always-on machine is no big deal. But that route didn't work, so full re-processing it had to be.

Quote:
Originally Posted by nbwriter View Post
Assuming you have a 1080p TV, 520p content will be passable, but cannot be considered HD (technically). The secret is to optimize 520p content or find a 720p source of the same content and still optimize, so you're then making best use of your TV resolution (whatever screen size you have).
That's the route I went for in the end, but with an intervening bicubic enlargement from 512 to 720 via VDub on the lo-res clips to match the larger format ones. For reference purposes, in the files used, Leigh 2 (DVD335) is 512x384, while Leigh 1 (DVD858) is 714x524, with a final output to 720x540 for both. What's strange to me is that the enlarged clips i.e. DVD335 (in the example I'll get to) in appearance seem of a higher quality than the native 720 clips used. The 'matix cell' effect seen in the darker areas of Scene 7 in the example I'll post look much more obvious than elsewhere. And that clip was at the higher resolution. While one hopes such artefacts will go unnoticed by casual viewers, plainly it would be better if they weren't there at all.

Quote:
Originally Posted by nbwriter View Post
I'm not sure what a "FF link" is, but yes, I've had an interest in video production since forever (more of an Art than a science, once you get into it). But alot of it is geeky, super-geeky, so grasping the basics of optimization first is the way forward.
My apologies - 'FF' is short for File Factory, who provide a file hosting service enabling uploading and downloading of files for communities.
I've uploaded an example of my effort mentioned above here: Warning - adult content:
http://www.filefactory.com/file/62o9...0mix)%20v3.rar
Password for the RAR file, should you choose to view it is: VEF

One thing I'm really unhappy about, (although it's there in the original rip too) is the colour drift in Scene 1. No processing filter I tried (unless I went for a cartoon-like effect) would eliminate the shifting subtle pysychedelic green and purple tones from the allegedly white bed sheet (and as an ex-art student it niggles me that those opposite colours are telling me ... something), nor the wandering flesh tones when the camera is zoomed in on the model herself.

I'd have liked to have fixed any or all of those problems, but y'know ... the next project beckons.

Last edited by Dvder; 04-25-2017 at 12:01 AM.. Reason: password added
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Old 04-25-2017, 05:32 PM   #13
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Default Digital Vid Editing: Grasping The Basics...

Dear Contributors,

Thanks to Dvder for generously posting his work. This is what it's all about

Quote:
bicubic enlargement from 512 to 720
Upscaling resolution to 720p will not garner any advantages in the output file due to the simple reason you're asking your software to stretch each pixel. What will happen is that your film will look washed-out (a saturation problem) and ghosting may occur (the pixel stretching problem: basically shadows and outlines are enlarged).

Although it goes against logic, a better route here is to reduce 720p content to 512p - so you obtain a high def output file. (Each pixel is being more tightly packed into each frame, a trick professional graphics artists use all the time).

You can easily see how this "reduction technique" works if you have a HD jpeg at 3000px x 3000px and reduce it to 1500 x 1500, you finish up with a picture that has super-definition on your screen!

Quote:
DivX 6 plugin in VirtualDub for re-coding...
Hmm.. I'm not sure who gave you this nugget of advice, but DivX always performed poorly on Microsoft Windows PCs. This is wholey to do with Microsoft's myopic coding (in their OS) supporting only "the chosen few" codecs that the company preferred: MPEG4, MPEG2, WMV.

Pro coders like YIFY go for MPEG4 using the MP4 container, although I prefer MPEG4 avi coz AVI can be further optimized, once you know what you're doing...

Resetting, or changing keyframe intervals in an AVI file will probably lead to MORE jitter (sync issues) since these are pre-set at the encoding stage. Straight re-encoding into MPEG4 from a source file will just avoid that altogether.

Quote:
I'm intrigued by the suggestion of altering the file header information. Presumably that'd be via a hex editior?
Going to the hex level on video files is not advisable, rather a simple tool called DivFix will repair missing or corrupt header information in source files, outputting a file that has less errors. (Its a depreciated tool, but many a pro-coder swears by it).

Quote:
I estimated 25 fps, at 720x540 with 32 bit colour depth should still leave a whole heap of spare cycles on a 3.4 GHz processor
I have my doubts, if I've understood you correctly, you were re-processing every single frame of a source file using DivX Plugin and VirtualDub.. On Core4 it will thrash through all the pixels per frame like a combine harvester on jet fuel... I just hope you have a high-spec cooling fan fitted over your CPU!

Quote:
No processing filter I tried (unless I went for a cartoon-like effect) would eliminate the shifting subtle pysychedelic green and purple tones from the allegedly white bed sheet
Ahh...I see.... You probably took the route here of a filter in VirtualDub, right? From my experience, if you wish for "crisper" whites in videos consider (the much simpler factors) of contrast or/and gamma levels- these can be finely adjusted in Videopad (for example). Videopad isnt a pro-level editor, but it does the job...

Final thoughts:

Reviewing "Lisa Phillips - Leigh Nearly Naked", I reckon you had minor contrast, gamma and color saturation issues in Scene 1. But the saturation issue isnt there in later scenes, so well done. Ghosting and jitter have been avoided, I suspect, due to the high quality source files you were working with. Full marks, too, for going with MP3 audio at 192 Kbps, that's how the pros do it! (Lovely crisp audio with MP3 every time)

Kind Regards NB
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Old 04-26-2017, 05:54 PM   #14
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Thanks for the tips and review NB. I'll certainly be considering them further for future projects.

One thing I hadn't mentioned about the problematic Scene 1 was that I'd cropped out (almost) all the picture edge tracking noise from what must have originated from (I guess) a VHS tape loaded camera, so the resolution in terms of picture dimension and colour 'bleed' was never going to be top grade, at least with my level of expertise and available time. All I can claim is that to me it looks 'better' than the source file, unwanted video artefacts notwithstanding.

While I did use - after trying out multiple settings - the contrast/brightness and hue/saturation/value filters in VDub for livening up what began as a rather washed out and muddy image, I may try starting with adjusting the histogram setting in a similar situation in the future.

The next bootleg mashup in prep uses 640x480 clips which look to be of fairly even quality, so I'll be careful to see after your comments if upscaling to 540p improves the image quality or makes it worse.

I really appreciate the investment of your time and your suggestions in giving your review. Thanks again.
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Old 05-02-2017, 04:17 PM   #15
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Default VirtualDub Issues: The Encoding Route

Dear Contributors,

For Dvder: No problem, I appreciate anyone who "has a go" at what amounts to a demanding technical challenge. (Many starters dont even know the basics of encoding, to be honest).

I'm only a tinkerer in encoding terms, not in the league of YIFY (whose MPEG-4 encodes are works of beauty). I doubt he's re-processing every frame via VirtualDub, though.

VirtualDub has a nice error mode that will fix AVI indexes, but you put this beast into "full processing mode" and your CPU will be screaming for mercy (and you'll end up with huge, unmanagable files).

If you re-save an avi file using VirtualDub (chosing stream-mode) I have heard this can fix problematic video. But for me, that's only a starting point. The source file needs to be fully defragmented (as one continuous stream) on your hard disk for starters. I would ditch DivX for MPEG-4 native (if you're still using Windows 7) just to cut down on the sync issues you'll encounter with DivX (You cant believe all the hype around encoders like DivX, the secret is to understand which encoder decompresses frames best on your operating system).

If you're sticking with VirtualDub to change gamma and contrast, you will be ice skating up hill for some time, I fear. If memory serves, one has to be in full processing mode to apply filters, or adjust the Luma histogram. (And you may be dancing in the dark, so to speak, unless you have a correctly set Luma histogram as a reference point for your project).

Consider, if you wish, a good real time editor like Videopad (NCH Software) or if money is no object, Adobe Premiere (used by the TV and film pros). Unless you can finely adjust your video file then preview it before encoding, you're kinda doubling your workload.

The Old VHS Cams And Decks:

Magnetic tape tech, of course, always had tracking issues (due to the rollers used to transfer images). Sounds kinda quaint, now, dont it? Very difficult to remove artefacts that were transferred to a digital format from magnetic tape. The artefacts basically become part of the encoding. I would go for editing out content below the 1 second threshold to address this issue (that can be done with Videopad or Premiere), then I'd apply a smoothing filter (but very finely adjusted) to iron out any tiny artefacts.

Upscaling from 480p to 540p will probably result in "blocky" video due to the pixel stretching issue. You'll notice this particularly in darker areas of the video. I'd take the route of defragging the 480p content you have, optimize its AVI indexes and headers, then encode it as a HQ MPEG-4 avi or mp4 file, using MP3 lossy stereo audio (at 128 kbps or above). You may be surprized how good the results are using that route.

Kind Regards NB

Last edited by nbwriter; 05-02-2017 at 04:20 PM.. Reason: text tidy up
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