So I'm capturing from a PAL VHS player (S-Video into a Magewell Pro Capture HDMI card), using VirtualDub, to a raw AVI file. What resolution should I be capturing at (assuming it's encoded onto AVI at 1:1), i.e. 720x576, or 768x576?
I plan to re-encode these raw captures to H.264 further down the line, but what should I be using at this initial stage? I notice some other capture cards that do the encoding to H264 themselves will encode the video (according to VLC) at 720x576, but when I take a screenshot using VLC, the resolution of the PNG file is 785x576. However i've taken further screen captures at other software where the resolution of the PNG file (again snapped using VLC) is 720x576.
So i'm baffled.
What should I be capturing at for a raw AVI file, for a standard 4:3 PAL Video?
I know PAL doesn't specify a horizontal resolution, but there must be some sort of standard, no?
I notice the properties in the "Capture Filter" option in VirtualDub say 720x576, yet the default resolution it wants to output is 768x576
[Attachment 55741 - Click to enlarge]
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Last edited by bergqvistjl; 5th Nov 2020 at 12:40.
I do not know where that above graphic comes from but it is certainly not from vdub.
You do appear to be confused with pixel aspect ratio and display aspect ratio. And both will vary according to what codec you capture in. For a start, most AVI containers do not support a valid DAR.
It is my understanding that the tech spec of converting from an analog signal (VHS) to a digital format is limited to a horizontal definition of 720 pixels. PAL supports a vertical definition of 576 pixels. So the maximum spec for most capture software is 720*576.
Now if you display 720*576 at 4:3 you will indeed get 768*576 (576/3*4 = 768). So it follows if your capture software support 768*576 then you can natively get 4:3 at 1:1. But I do not think vdub supports that.
For 4:3 materials capture at 720 and then crop off the 16 black pixels to get to 704x576, and when encoding to the final format give the pixel an aspect ratio of 12:11 so 704/576 x 12/11 = 4/3. If you set the aspect ratio to 4:3 from 720x576 it will be wrong, not enough for the average person to notice it but the frame will be horizontally squeezed by 16 pixels. 720 became the standard after D8. DV and DVD, any other analog format that is converted to digital is 704 by standard.
All capture cards capture the active video area at 704 pixels, I don't think you would gain anything from capturing 768 since the capture card will most likely be upconverting from 720 to 768 on the fly, But if you want square pixel you can capture at that resolution but the aspect ratio will be wrong as I explained above.
VirtualDub (or at least with my card) lets me capture at 768x576.
Last edited by bergqvistjl; 5th Nov 2020 at 14:11.
You should have mentioned youtube in the first post because it has it's own workflow, For youtube to not butcher your videos with a very low compression rate you would have to have at least a video at 720x1280 but since this is an obsolete resolution in terms of display panels supporting it you can go straight to 1440x1080. First capture at 720x576, then crop to 704x576 (this is a lossless process with vdub), these will be your master files. From here resize to 1440x1080 (this is a lossy process but vdub has good filters for this), the file will be huge but after uploading to youtube you can then delete the resized video.
It should look somehow like this:
Last edited by dellsam34; 5th Nov 2020 at 14:18.
Last edited by bergqvistjl; 5th Nov 2020 at 14:44.
704x576/704x480 are standard resolutions, I haven't come across any device that doesn't support them, And it is part of the DVD standard as well. But yes in a computer environment any resolution should work because software players have their own aspect ratio and scaling functions.
Last edited by bergqvistjl; 5th Nov 2020 at 14:50.
Remember that 704*576 is NOT 4:3 that will still equate to 768*576. 1440*1080 is 4:3 but you could go lower at 960*720 without ytube causing damage.
Yes, Neither 704x576 nor 720x576 have an aspect ratio, You will have to either set the aspect ratio by giving the pixel a shape or resize to 1440x1080 and the pixels will be square.
OK, so here is my workflow:
I capture at 720x576, so my captured video has a DAR of 5:4 & PAR of 1:1
I then crop 8 pixels off either side so the video is now 704x576 (DAR 11:9 PAR 1:1)
I then stretch that now-cropped video horizontally to 768x576 (DAR of 4:3 PAR 1:1)
I then upscale this to 1440x1080.
is this right?
I've also noticed I appear to get similar & slightly sharper results if I capture at 786x576, then crop (still in virtualdub as part of the capture 8 + 10 pixels off either side), thus giving me a 768x576 file with the correct proportions (albeit offset by a pixel on one side), thus not needing that further middle layer of stretching.
Last edited by bergqvistjl; 5th Nov 2020 at 15:28.
Just use 768x576, it gives square pixels within 4:3 aspect ratio and Virtualdub2 supports this mode. I do not crop anything.
Anyway, here is the raw image captured at 768x576, with no post-processing/cropping/resizing at all.
[Attachment 55744 - Click to enlarge]
and here is the same image captured 720x576, cropped to 704x576 then stretched again to 768x576
[Attachment 55745 - Click to enlarge]
which is the correct one?
Last edited by bergqvistjl; 5th Nov 2020 at 16:00.
The 2nd one since it removes the crud (16 pixels)
And you do not upscale. You resize. That compensates for the non 4:3 704*576. No need for the intermediate 768*576 except for your own purposes rather that the upload. Resizing from the 704 >> 768 involves two re-encodes.
Capture at 720x576 not 768, you are not gaining any resolution with 768, the card is just adding 48 black pixels.
Then crop 16 pixels off so the video is now 704x576, It doesn't have to be 8 on each side depends on how much junk on each side.
Then RESIZE to 1440x1080, not upscale.
Edit: You might be using an old version of vdub that doesn't have the resize filter, try vdub2.
Last edited by dellsam34; 5th Nov 2020 at 16:35.
I've just done some experimentation and I've found capturing the video at 788x576, and using VirtualDub's built-in cropper tool to crop 10 pixels off either-side gives me an identical picture, just higher quality, than capturing it at 720x576, cropping and then resizing again.
Just remember that you have already been told.
Upload that 768*576 to ytube and they will resize that to 640*480.
I just used YouTube as an example of a service that will (apparently) ignore the PAR on your video, thus neccessatating that my video should look correct when displayed with a PAR of 1:1.
Last edited by bergqvistjl; 5th Nov 2020 at 17:02.
I don't think capturing at 768 has any effect on the quality as clearly shown in your screen shots that 768 just adds 24 black pixels on each side, it's either a placebo effect or a software is doing something weird with 720x576 captures, We showed you the right resolution to save your masters and what to do if you want to upload to youtube, the rest is your business.
Anyway, I'm capturing the video at 788, and cropping 10 pixels (the black bars) off either side, still in the capture part of VirtualDub, which gives me a 768x576 AVI, with no black bars, and at the right proportions, without me needing to do any further resizing
Last edited by bergqvistjl; 5th Nov 2020 at 17:33.
Well that is also your call. Again, you have been told, you do not have to take my word for it - there is plenty of info on line of the maximum effective width of SD analogue to digital. Or do you also not accept why DVD, which is also based on the same system, adopted 720 for both PAL and NTSC.
Last edited by bergqvistjl; 5th Nov 2020 at 17:56.
I am not writing about the actual shape of the pixels but the actual number of them.
Capturing anything higher than 720 simply distorts the image. But it's your video so if you want to do it then go ahead.
As far as I know, PAL 4:3 DVD is encoded at 720x576 (which is 5:4), however the pixels are non-square, so when displayed like that, it translates to an effective resolution of 768x576, which corresponds to 4:3, is this correct?
but the second image (720x480 cropped to 704 then resized to 768x480) looks like a more
accurate A/R to me - the circular shapes look more balanced. But it's a small difference. Usually only the real sticklers notice it
What you do not understand is the relationship of analog to digital. The appropriate Rec stated that the horizontal width is limited to 720 pixels with 704 being the number of active video pixels. This is constant whatever codec you choose to capture in.
As for DVD, while 704*576 is a valid part of the spec one rarely sees such a dvd these days. There is discussion about this in other topics and is not really relevant here.
But it seems that your capture device can go beyond 720 pixels. Most devices, mine included, are locked at that. But you are still going to get crud and you would have to crop that away. Would your original capture still look ok after the crop and resize back to 768 ? There does not appear much difference in your two images but the simple maths infers that the second is the most accurate.
Let's keep this all straightforward (keeping it predominantly as PAL, since that's what you're talking about)...
- There's the Analog video on you cam/vcr, etc.
- There's the Digital stream after conversion from analog, BUT BEFORE BEING ENCODED AND STORED on hdd.
- There's the Digital encoded file, AS STORED on your hdd.
- There's the Digital encoded file, AS SHOWN on your monitor.
- And there's the version you want/need to send to Youtube.
#2 when captured by INDUSTRY STANDARD cards/devices (which follow BT.601 rules) is 720x576, or 702 or 704x576*. That's it. It is either 4:3 DAR or 16:9 DAR (much rarer). Either one of those DARs attached to any of those resolutions means the PAR is non-square (aka NOT 1:1). This is how it is coming in, REGARDLESS of what you set in your settings for capture encoding & storage. So don't waste.
#3 is where you get to decide how it is first stored & encoded. If you are trying to MAINTAIN BEST QUALITY, you will NOT do any resizing yet, and you will encode to lossless AVI. Thus, you should have it stored as 720x576 or 704x576 (possibly 702, but that isn't mod4 so might cause problems with some encoders). If your encoded/stored format supports DAR or PAR flagging (you only need to do 1 not both), here you can put this in. But it doesn't really matter if it doesn't support it, because this is just your storage format. So AVI, which doesn't normally support flagging is still ok. Note that even when some containers, like AVI, don't support AR flagging, the codec still might.
#4 when you VIEW it, you are now seeing how a certain player reads such a file and maps it to your monitor screen (whether in a window or in fullscreen). If you view this in a player that doesn't support flagging, and you didn't encode any AR flags in either the container nor the codec stream, this will now display on your (1:1) monitor as wrong/stretched. If you use a player that allows for adjustment of AR (e.g. VLC), you can just tell it to use that AR and it will correct your image's display on the screen, though it does nothing to the underlying file. If you use a player that supports AR flags, AND you were able to encode those flags, that player should be able to make that AR correction automatically. At this point, even though it is still stored at, say 704x576, it will show up as 768x576 (when using 4:3 DAR and being shown a 100% zoom in a window).
#5 if you want YT to give you the best download/streaming playback quality, you have to force it by uploading a 1080-level copy. That way, it (YT) allocates much more bitrate to the down-rezzed encodes it puts out. For 4:3 DAR, you RESIZE from 720/704 x 576 straight to 1440x1080 (best to apply QTGMC or similar deinterlacing as well to make it p60 instead of p30 or Interlaced - since that's what the original was - and p60 will look much smoother on YT). You should ignore the DAR or PAR as stored and let the final encoder treat it as square pixelled and include the necessary stretch manually, or depending on the encoder, let it read the AR flag and just tell it that final res (1440x1080) and it should auto give you a 1:1 PAR output.
Notice, you didn't need to resize AT ALL until going to #5. You didn't really need to crop at all unless you wanted to get rid of the black bars in #2->#3. You didn't need to do a lossy encode except in #5. This setup gives you the best quality sampling resolution (#2), the best quality encoding (#3 & #5), and the least destructive modifications (#2/3 or nothing when cropping, #5 when resizing, and #5 when deinterlacing).
Also, I'm pretty confident that your "768" setting is NOT what it's capturing stream as, but what it's being encoded/stored as, thus it is resizing if you do that. Maybe it's adding sharpening as well. Both not a good idea for encoders.
*occasionally a card allows for 1/2 or 1/4 D1 capture options natively, but those aren't recommended for quality.
Last edited by Cornucopia; 5th Nov 2020 at 19:24.
- There's the Analog video on you cam/vcr, etc.
You also seem to have a hard time understanding why 704x576 gets resized to 768x576 or 640x480 or 960x720.