HDV rendering quality issues

philfort wrote on 1/7/2006, 12:23 AM

So I've got HDV footage that I've rendered into Cineform HD. Now I'm rendering my final product back to HDV. I've got a lot of snowy scenes, and I'm seeing noticeable quality loss when doing this. Mainly, the smooth snowy background has faint but visible pinkish squares on it.

Here's an example, where I upped the contrast afterwards to show the difference (it's not quite so extreme in reality, but I wanted to illustrate the difference - it's still *very* noticeable and distracting when watching the resulting product on my computer monitor): On the left is the Cineform HD, and the right is the HDV I rendered.
http://www.mtnphil.com/Temp/HDV-Compare.png

Is this to be expected?

The documentation says:
"If your intermediate files were rendered using the CineForm HD codec, you won't need to replace the intermediate files with the transport streams."

This suggests to me that going from HDV->CineForm HD->HDV shouldn't show a noticeable quality loss. e.g. it wouldn't be noticeably worse than just doing a bit-copy of the original HDV - which presumably I would get if I replaced the intermediate files with the transport streams.
(Note that I'm assuming no re-rendering needs to be done - there are no Fx used here).

My project settings were:
HDV 1080-60i (1440x1080, 29.970fps)

I rendered intermediate files using the "HDV 1080-60i intermediate" template.

I rendered the final HDV output as "Main Concept MPEG-2 (*.mpg)" with the "HDV 1080-60i" template.

Am I doing something wrong?

Comments

farss wrote on 1/7/2006, 1:53 AM

The HDV image on the right sure has some problems, not only the macroblocking but also the color shift.
Don't really have any answers and I don't see that you're doing anything wrong so maybe a bit of detective work is in order. Need to determine if the conversion to the DI has introduced more detail that the encoder can't cope with when it's encoded back to HDV or if it's that the MC encoder is nowehere near as good as the one in the camera.
I'd take a frame from the original m2t file and compare it with the matching frame from the CF DI. Easy enough to do, put one on the top track and the other on the bottom track. Set top track to 50% opacity in the track header and add the Invert FX to the top track at 100% Inversion. What you see on the Preview monitor at Best is the difference, should be just flat grey.
Bob.

fldave wrote on 1/7/2006, 6:50 AM

For the final render HDV 1080-60i template, go into custom\video properties and make sure that the Quality slider is move all the way to the right. I believe it is normally 15, and for best quality I move mine to the rar right value 31. I also set my project properties to Best.

I would be curious to see the quality difference using the original m2t instead of the intermediate for the final render, but you may not have the time to experiment.

Edited: I just looked and the default template for HDV 1080-60i has the quality slider at halfway mark. I have set up my own template HDV 1080-60i High Quality that has the video setting at 31 and use that exclusively.

Wes C. Attle wrote on 1/7/2006, 6:56 AM

Make sure you did not select "Use Microsoft DV Codec" in the Vegas Video Preferences window. I think I discovered that this will force your HDV intermediate render via the Microsoft codec using HDV resolution. Not only does it look bad, it is really slow!

mark-woollard wrote on 1/7/2006, 7:36 AM

philfort

My workflow is similar to your's except:
1) I capture HDV with HD Connect and set it to do a simultaneous conversion to CF intermediate (medium quality), and
2) I encode to m2t with the quality slide at "best" as fldave suggests above.

I have not encountered any blocky artifacts or colour shifts like you are seeing. Perhaps that's because I haven't shot any white snow scenes that would bring it out.

Let us know if playing with the render quality slider makes a difference.

Mark

Wolfgang S. wrote on 1/7/2006, 8:22 AM

Are you sure that you are using Vegas 6c, and not the oder Vegas 6b?Earlier tests with the older Cineform codec in Vegas6c have shown a color shift, when rendering to the Cineform codec.

http://videotreffpunkt.com/tutorials/Intermediates/Intermediates%20Part%201.html

But I have not tested that for the later codec version, that is part of Vegas 6c.

David Newman wrote on 1/7/2006, 9:44 AM

Yes definitely use the Vegas 6c or the latest Connect HD release for the best quality (using v2.3 of the CineForm codec.) The quality analysis post here: HDVQualityAnalysis051011 uses the v2.3 codec. The macro-blocking in the output is definitely an MPEG encoder issue (which shouldn't be happening in that image example.) MPEG encoder maybe bit-rate starved if the detail is very high in the rest of the frame and or there is a lot of motion.

David Newman
CTO, CineForm

philfort wrote on 1/7/2006, 10:27 AM

Thanks for everyone's help!

I'm using 6b. I'll upgrade to 6c, re-render the intermediate files and let you know what happens.
(I tried rendering the HDV with the quality slider all the way up to 31, but it made almost no difference - in fact it looked just a little worse, like there was more detail in the blocks or something)

Note that the link I posted above was the result of me upping the contrast to show the problem more clearly.
Here are examples of the original frames (HDV output frame on the right, again)
http://www.mtnphil.com/Temp/HDV-Compare-No-Contrast.png
You can see it's way more subtle, but you can see the "blockiness" on the right frame... when it's in motion, the blocks are much more noticeable show up as a jiggling pink and blue mosaic.

Wolfgang S. wrote on 1/7/2006, 10:48 AM

As said, there is a color shift in that version - you see that also quite well in my link. Make the free update zu 6.0c, and test it again.

philfort wrote on 1/7/2006, 10:53 AM

Ok, doing that now, I'll let you know it goes.

Here's an image that shows the original HDV, and what happens if I render from that original (I added a piece of text in the corner of the footage, so Vegas was forced to rerender each frame).
http://www.mtnphil.com/Temp/HDV-Compare2.png
You can see a little blockiness in the HDV->HDV, but it's much more apparent in the Cineform->HDV, probably due to the color shift you guys mentioned.

Hopefully updating to 6.0c will fix this.

fldave wrote on 1/7/2006, 11:15 AM

By the way Wolfgang, thanks for the informative link to your detailed testing. Confirmed why I try to shift back from Intermediate to original m2t for final render. Interesting that the quality slider had little effect.

philfort wrote on 1/7/2006, 11:57 AM

It seems to be worse with Vegas 6.0c.
These are the results I'm getting now:
http://www.mtnphil.com/Temp/HDV-Compare6c.png

Now the Cineform HD intermediate file seems to be showing a good amount of color shift, where before it only appeared prominently once it was rendered back to HDV from the Cineform HD.

(Maybe it just shows up more because the original HDV frame is more blocky in this sample? I noticed, stepping through the orignal HDV footage (from a Sony HDR-HC1), that every third frame is smoother than the other two, which show some blockiness).

Anyway, clearly the footage is better w/o going through the Cineform intermediate.

Wolfgang S. wrote on 1/7/2006, 1:32 PM

> By the way Wolfgang, thanks for the informative link to your detailed
> testing. Confirmed why I try to shift back from Intermediate to original
> m2t for final render. Interesting that the quality slider had little effect.

You are welcome.

But be aware that even the rendering m2t->m2t shows a measureable drop in quality - at a very similar size compared with a route where you render m2t-> Canopus HQ -> m2t. In other words: you cannot avoid a (small) quality drop, even if you work with proxys and Gearshift, and even if you swith back to your original footage before rendering to your final video. And unfortunately, at least in my tests the Canopus HQ codec performed better, compared with the older version of the Cineform codec.

I am a little bit shoked about the last link from philfort. That seems to prove a still a color shift when rendering to the Intermediate. Have you worked with the original templates, or changed something (e.g. the color space that is used)?