Suggestions for quality settings

[DaveL]

Hi, I'm capturing VHS tapes that are of so-so quality using HQ via blackmagic intensity USB. It's basically working fine, BUT I'm trying to set the quality settings (the HQ settings on the device preset menus) to be "appropriate."

What I mean is that I don't want to use the disk space to capture high quality HQ, but use the custom settings to lower the quality as appropriate for so-so VHS tapes and lower the size the captured files.

I'm having a hard time understanding what the 2 quality settings do. I can change their values and get different quality captures, but I can't find anywhere what the values mean and what "reasonable" settings might be.

Does anyone have suggestions as a starting point, or can point me to some detailed information on these settings? Thanks

[DaveL]

With additional searches, I found more information on HQ settings.

However, if anyone has been through this and has a starting point for the settings to optimize files size for VHS level of quality, that would be helpful. Thanks.

[BernH]

If these are settings in the BlackMagic Intensity Shuttle and specific to that hardware, you may find your answers at the Black Magic Forums.

If you are talking about the HQ and HQX GV codecs, the main difference, aside from the math involved in the compression schemes, is that the HQX codex is capable of 10bit colour.

Aside from that, VHS is a fairly low quality Standard Definition video. DVD is a higher quality standard definition video.

That said, top quality Digital SD is 720x480 in NTSC land and 720x576 in PAL land. VHS, since it is an analog signal, is measured in TV lines of vertical resolution. Top Quality NTSC has 525 lines and PAL has 625. VHS tended to be somewhere in the 250 lines of resolution area, but this could vary a bit depending on the quality of the deck and the tape. When you convert all this into digital speak, it means that your VHS has about an equivalent resolution to a standard def signal that is about half the dimensions of the top quality digital SD. But, when you half the vertical, you should also half the horizontal, so you are really at about 1/4 total resolution. A common resolution used for VHS quality is 352x240, as it is a standard resolution that is close to the VHS resolution.

[antonsvideo]

With additional searches, I found more information on HQ settings.

However, if anyone has been through this and has a starting point for the settings to optimize files size for VHS level of quality, that would be helpful. Thanks.

just capture your VHS to mpeg2 custom at 15M

[DaveL]

Thanks.
Anton, you suggest this because MPEG2 will do better compression/file size for "VHS quality" levels than HQ will?

[BernH]

Thanks.
Anton, you suggest this because MPEG2 will do better compression/file size for "VHS quality" levels than HQ will?

Based on that question, I assume you have been referring to the GV HQ codec. If that is the case, I would suggest that you use the GV HQ codec picking one of the online standard or fine presets, just because it is the native codec for Edius and it is a very good codec, and stands up well to processing.

Here is a nice little explaination.

http://forum.grassvalley.com/forum/showthread.php?t=7354

and a link to the codec whitpapers

https://www.grassvalley.com/docs/WhitePapers/professional/edius/GVB-1-0027A-EN-WP_Intro_HQX.pdf

[Liverpool TV]

Hi Bern.

You are absolutely correct about using the GV HQ/X codecs, especially over low bitrate MPEG2.

Although I suspect that the use of the term HQ by Dave, may be a reference to High Quality if he's using a capture setup outside of Edius, maybe it's BM capture software and that's what it calls it. If so, depending on the card and version of Edius, it may be worth setting up the card as a capture device inside Edius and use Edius and GV HQ to capture.

If I've misunderstood and the card's capture is via Edius and not the BM software, then setting the GV HQ setting manually to maximum, would allow for testing any potential difference.

Although it's worth bearing in mind that the original video quality may simply be not very good. The worse the condition, tracking, scanning, noise etc. It's going to need high bitrates and possibly a good TBC.

Cheers,
Dave.

[DaveL]

Sorry for the confusion: Yes, I was referring to the GV HQ codec settings.
I have found info on what the GV HQ codec settings do, at least conceptually.

Of course, ultimately I need to keep doing trial & error of the settings.
But, I was hoping there might be some information on what settings will give me good compromise of quality vs file size when capturing VHS level of video quality. It takes a lot of trial cases to dial this in, and was hoping someone could give me a leg up. Thanks

[antonsvideo]

Thanks.
Anton, you suggest this because MPEG2 will do better compression/file size for "VHS quality" levels than HQ will?

I suggested it because you want smaller files and mpeg2 at 15M is ok

HQ Standard is better and way smaller than HQ fine

in my case, disk space is no issue so I would choose HQ standard or fine

[Liverpool TV]

Hi Dave.

Maybe try this test first. Do a capture at maximum HQ settings, this will be a large file but it's just to test. Then compare this to the lower HQ settings that you've tried.

If you see a big difference then this may suggest that you need to be looking at high settings. If on the other hand you don't see much in it, this may suggest that you are probably close to the most efficient bitrate anyway, and it may simply be down to the source footage/input quality.

In any event. If you are editing old stuff to then archive it, it may be worth putting up with large files until you've got your master. Then maybe transcode the master to a high quality MP4 using X264/Handbrake. This will give you a great looking and future proofed multi platform playback file, at a reasonably small file size. You can then just delete the large project files once you're happy with the final MP4.

If on the other hand, you are planning to digitise to a format for later editing. Then you're pretty much stuck with higher bitrate files to maintain high quality easily editable files.

BTW, I've been film making since season 4 ST DS9 on VHS on a colour TV :)

Cheers,
Dave

[BernH]

In any event. If you are editing old stuff to then archive it, it may be worth putting up with large files until you've got your master. Then maybe transcode the master to a high quality MP4 using X264/Handbrake. This will give you a great looking and future proofed multi platform playback file, at a reasonably small file size. You can then just delete the large project files once you're happy with the final MP4.

If on the other hand, you are planning to digitise to a format for later editing. Then you're pretty much stuck with higher bitrate files to maintain high quality easily editable files.

That is the pretty much exact method(s) I would use. Capture at a relatively high quality/high bitrate codec with as little compression as I can, to try to preserve as much quality as possible. Then convert for archive or edit and produce as required. Don't get too caught up on the adjustments in the HQ codec. Pick the Standard or Fine preset and go with it. From what I gather, the main difference in them is the amount of quantization applied, (the Q slider in the settings). Less quantization means the image is processed in smaller blocks and therefore less "similar" data in a block to apply the lossy compression to, resulting in larger files with a "finer" granularity in the quantization matrix, less compression and higher bitrates. This is why the fine files are larger than the standard file.

If you are planning on archiving, you probably don't want to keep it in the HQ codec, so trying to match it for VHS is pointless, but it will give you a good high quality file for the step of making your small size archive file. If you keep it in the HQ codec, you will only be able to view the files on your Edius system or as a MOV file in Quicktime with the Grass Valley codecs installed.

I have been dealing with and learning about various codecs for 20 plus years, and have actually developed a half to 3/4 day course on the subject that I will be teaching at the post house / co-op I work at. It is targeted at editors that are non-technical. Without getting into the meat and math of it too much, there are a couple of points I will throw out here.

1. There are basically 3 categories of codec. Aquisition, Mezzanine (a.k.a. Post), and Delivery. The Mezzanine codecs, which are the preferred ones to use in editing, are less compressed and higher bitrate, making your editing cleaner and more responsive, but taking up more drive space.

2. Capturing and processing in Mezzanine codecs minimizes or avoids un-necessary compression artifacts created by any effects or transition processing. You can still get artifacting from noisy or unstable source files, and sometime your choice of codec can change how much artifacting you get, but generally less compression means less artifacts.

[BernH]

It doesn't work this way. Blocks are the same, just Q is lower, so bitrate is higher.
Size controls what maximum bitrate is allowed. 100 means in theory that maximum bitrate can be same as uncompressed. Depending on the source nature either Q or Max size gets precedence. For Size=100 it most likely that quantisation will be controlling bitrate for all the time. If you use Q=4 and Size=20 than some scenes will be "restricted" by Q settings, others by size settings. If you know your disk is slow than Size allows you to restrict any peak to (size) percentage of the uncompressed video. Q doesn't really tell you what bitrate will be used as this depends on complexity of the source. Q is very similar to CRF in x264. Same value should give about relatively same visual quality, where bitrate can be very different depending on the source. Max Size is there to enforce hard peak restrictions.

Andrew, as I said, I try to tailor my codec explainations for the non-technical. Sometimes that means that the explainations are not 100% accurate, in detail, but more of a generalized laymans view. This is particularly true for the GV HQ/HQX codecs since they don't have bitrate controls or pre-defined bitrate settings, but instead vary the bitrate based on content and quantization, making this one of the harder codecs to understand how the settings work, particularly if you are looking for a mathematical equation to apply for bitrate calculations.

I never said the Q dictates the bitrate, but that it controls the Quantizer, which, depending on how the image is quantized, can control the agressiveness of the encoder and ultimately the bitrate.

I am a technician by trade, I appreciate your attention to the small details, as I share that view, but the small details scare most people and cloud the issues as they are not technical minded, so simplified explainations are needed for them to get a general overview. Simplifying things generally requires less than 100% accuracy and some fudging of numbers.

[DaveL]

Thanks all for input. I have an issue however.

When I look at the compression settings, the only options I have are Uncompressed, GV HQ, and GV HQX. No MPEG
I wanted to try MPEG per Anton's suggestion, it's not there.
Suggestions on why that codec is not on the list for BM shuttle at 720x480i?

Thanks

[BernH]

I have an Inensity Pro card. I can make a preset that uses the GV codecs, AVC Intra 100, MPEG2, and a couple of XDCAM in HD, but in SD I only have the GV codecs.

Looks like the GV codecs are your only option for analog SD, same as me. That isn't a bad thing though. They are really good codecs.

[BernH]

No IMX options for SD? I think this use to be available.

It may have been available before opening up the I/O to 3rd party devices, but I don't know, as I came to Edius when Version 7 was released.