Video Playback Quality

[sdculp]

I am capturing VHS tapes to my computer with DVD Express DX2 and turning the resultant videos into DVD video shows with ShowBiz 2. When I play back the ShowBiz videos on my 53 inch TV the color quality is not what I would expect. I will do my best to describe it: The picture is made up of tiny rectangles. Particularly with blue sky or similar objects where the color is rather uniform, the rectangles can’t seem to decide which shade of color to display, and the result is kind of a flickering, checkerboard effect. This effect is also visible on my 15 inch flat panel computer screen, although being much smaller they are not quite so easily seen.

What is causing this? Can it be fixed?

Thank you.

Stuart Culp

[tomlee59]

These are called macroblock artifacts. The way MPEG works is this: It subdivides each image into a number of blocks, each of which is processed individually. If the bitrate is sufficiently high, then each block is represented with good accuracy, and the image looks good. If the bitrate is too low, then you'll get visible artifacting.

VHS as a source is notorious for provoking these sorts of problems. The high noise level -- snow, jitter, etc. -- forces the consumption of a lot of the bits as the encoder desperately tries to accurately represent this crud. That leaves fewer bits to do real work.

To get the best results (which does not mean that the results will be good), use the highest bitrate you can, and employ smoothing filters that eliminate such noise before the encoder is engaged. Such noise-reduction filters will necessarily reduce sharpness, but that's still far better than what you're probably seeing.

Also, the quality of the capture card/box can make a huge difference. I haven't used yours, so I can't say whether it's good or not, but you may want to do some research to find out.

And if you are really gung-ho, and have the cash to burn, buy yourself a time-base corrector to eliminate timing jitter from the tape.

[guns1inger]

Can it be fixed ? - Not nicely after the fact. You will have to transfer again.

It appears that the device encodes automatically as it captures. What options does it give you for setting quality levels ? Do you get simplistic controls, such high/medium/low, or vague quality levels, such as EP/SP/LP etc ? Or can you set actual bitrates in Mbps or kbps values ?

For VHS captures I would recommend keeping the length down to less that 90 minutes per DVD sized file. You can stretch to to more if you filter and do 2-pass VBR encoding of the video, however this is not possible with on-the-fly realtime encoders.

[sdculp]

Thank you for the help. I can see that I have not been paying nearly enough attention to those parameters which affect recording quality--merely selecting default values which result in "good" instead of "best" and data rates of 1.3 instead of 4 mb/sec.

I'm doing some recapturing and will see how it works out. I think I am overwhelming my 1 gig of RAM, as it takes about as long to render as it does to capture, so it takes a long time to experiment.

I am also experiencing a lot of "failure to write" errors in ShowBiz as it tries to author. I am going to post a thread on "Failure to Write" soon to see if I can find the cause.

Stu

[tomlee59]

Here are some tips for capture:

1) Disable all apps that will compete with the capture app for the CPU's attention. Shut off networking (wireless especially), stop surfing the web on that machine, etc. Disconnect any peripherals that might reduce I/O bandwidth of the USB (or whatever) port you are capturing to.

2) Capture to a clean partition on the hard drive. The more fragmented the drive, the more likely it will be that there will be capture hiccups, errors, etc. You want a recently wiped partition so that the new data can be laid down contiguously.

3) Experiment with short clips to find good settings. Then -- and only then -- perform a full-length capture. It makes no sense to spend an hour or two capturing before looking at the result and finding that it didn't go well. Perform short-loop experiments first to converge on the right settings quickly.

4) Select the highest bitrates that you can practically support. Upper bounds are imposed by CPU and I/O capability, as well as by the playback device's limitations. For DVD, you want to keep peak bitrates below about 9Mb/s. Higher than that, and some standalone players will begin to choke.

5) Consider enabling noise reduction filters when capturing from a noisy source (such as a typical VHS tape). This reduces macroblock artifacting at the expense of a softening (blurring) of the image. Depending on which impairment is more objectionable to you, you may wish to use such a filter. Different products call it different things, so you may be forced to read some documentation. Yeah, I hate that too.

6) As guns1inger said, a real-time capture box can't make use of two-pass encoding, so you get what you get with one pass. Depending on the sophistication level of the capture hardware, this could be acceptable or just plain unwatchable. I own an older adstech box that is the probable ancestor of yours, and it does an ok job. Not great, not horrible. Just ok.

[jagabo]

I think I am overwhelming my 1 gig of RAM, as it takes about as long to render as it does to capture, so it takes a long time to experiment.

No, 1 GB RAM is sufficient for MPEG2 encoding. CPU speed is the problem.

[sdculp]

Thank you for the suggestions. All good advice!

Using ADS DVD Express DX2, Ulead Video Studio 11 and ShowBiz DVD 2 I created several short videos for a ShowBiz slide show. I captured both AVI and MPG versions of a 3 minute video with worst case colors (Caribbean aqua/blue/grey). I then did comparisons on the big screen TV. Prior to this I had not viewed unedited, raw captured videos on the TV and was surprised to see that neither AVI or MPG had any trace of artifacting!! It was only when AVI files were edited and rendered or whenever MPG files were rendered back into AVI that the artifacting showed up.

Here is a summary of the results using Ulead/AVI: “Clipped-Save Trimmed Video”__very bad, “Create Video File-DVD/VCD/SVCD/MPEG-NTSC DVD (4:3)”__ Usable.

Using Ulead/MPG: “Clip_Save Trimmed Video”, “MPG Optimizer”, “Create Video File- DVD/VCD/SVCD/MPEG-NTSC MPEG2” and “Custom MPG”—all usable.

It occurred to me that if the problem only occurred with Ulead, I might be able to edit and render in ShowBiz, even though SB trimming is not as accurate as UL The file types in SB are different than UL. AVI and MOV are two of the types which would be acceptable in SB slide shows. Using the AVI captured file, the AVI rendered file was artifacting. The MOV file was usable.

Because of the as-yet unsolved “Failure to Burn” prolem, and because artifacting seems to be limited to MPG files, I have used AVI “Clipped-Save Trimmed Video” as the quickest and easiest way to get trimmed videos for the slide show. This has proven to be the worst of the possibilities. However it may be possible that AVI files in the NTSC DVD (4:3) may be OK.

I have not yet tried Pinnacle Studio 12 editing because it just might confuse the situation, and because it seems not to be a product oriented problem.

The situation where the unedited files show no traces of artifacting but where edited files do so is confusing to me. I would appreciate any comments on this or any of the above experiments.

[guns1inger]

Start by analysing the footage. Media Info is a good place to start. Look at the details for the clips, noting especially the bitrates and codecs. Re-encoding footage using lossy codecs always needs to be done carefully. Using low bitrates, encoding multiple times, doing single instead of 2-pass encoding for VBR (Variable BitRate) can all have adverse effects.