Hdv Codec Research

[PappasArts]

I am doing research on HDV, and I have a few white papers on HDV and Mpeg. In this white paper by arthur Al Kovalick there is a mbs equivalent from IBP and what it is in I-frame image encoding. READ BELOW EXCERPT.............

-----------------BEGINNING----------------------
In the figure, the notations (IBP) and (I) are used. IBP refers to the most efficient form of MPEG also called Long-GOP MPEG. In this format, video frames are compressed in relation to the redundant image content of their nearest neighbor frames. This yields excellent compression metrics. So called I-frame compression is about 2.5 times less efficient than IBP but is easier to encode, decode and process. I-frame codecs don’t factor in the image activity of nearest neighbor frames so the coding is less efficient than its IBP cousin. So an HDV image encoded at 25 Mb/s (IBP) is roughly equivalent to an I-frame image encoding of about 60 Mb/s. So, when comparing two compression schemes, remember that the higher bit rate version may not necessarily provide the better image quality.
-------------------DONE-------------------------



What do you think about this?

If it's wrong or? Can you please state why it's wrong and then point to a white paper or study that backs up why it's wrong.

I am trying to write a HDV article and want to make sure the truth and facts are correct about how HDV is and compared to how other codecs perform. So far what I am starting to learn about HDV at 6 gop is it's quite efficient and a very advance codec without redundant compression schemes. I am in the very early stages of this research.



SOURCE for above info:

http://66.102.7.104/search?q=cache:R17K4mYwdN8J:www.pinnaclesys.com/BSD/liquidblue/English(US)/doc/WP_HDV_40804.pdf+++++++++++HDV+white+paper&hl=en&ie=UTF-8

PDF VERSION:
http://www.pinnaclesys.com/BSD/liquidblue/English(US)/doc/WP_HDV_40804.pdf



Michael Pappas

[Barry_Green]

The longer the GOP, the more effective and efficient the compression is. However, other issues come into play with long GOPs -- a significant shift in scenery (i.e., a cut to a different scene, for example) can really play havoc with a long GOP. In cases like that the picture may become quite fuzzy until the next GOP comes into play.

So long and short GOPs both have their advantages. In acquisition it's generally thought that the shorter GOP, the better -- Sony's professional MPEG-IMX camera uses I-frame only, so the equivalent GOP is, well, one frame. No B or P frames are used at all. As long as you've got an adequately-fat bit pipe, it can deliver superb results -- but it's basically the same as a DV or DigiBeta type of intraframe-only compression scheme at that point.

For delivery, long-form GOP is the norm. DVDs use a GOP of, what is it, usually 15 or even 18 frames? Satellite HD broadcasts use long GOPs as well. If you have to cram a lot of data into a small data pipe, the longer the GOP, the more efficient the compression.

As to the 25mbs vs. 60mbs comparison: they're comparing MPEG to MPEG. They're comparing I-frame-only MPEG against IBP MPEG. Presumably they're also comparing 4:2:0 vs. 4:2:0, etc. In those circumstances, yes, I'm sure their 25 vs. 60 is probably right. That however doesn't bear any relevance when comparing against other compression schemes: you can't take that 60 megabits number and then compare it against MJPG or DV50 or DV100, because while they're also DCT-based compression schemes, they're *different* -- and equivalent bitrates don't equate when you're talking about dissimilar codecs. So be clear: they're talking about I-frame-only MPEG at 60mbit vs. IBP MPEG at 25 megabit. And even then, it's still not truly possible to compare, because the motion rendition of I-frame-only MPEG will be far superior to that of long-form IBP MPEG.

I guess I'd say it like this: on a static scene, 4:2:0 I-frame-only MPEG at 60 megabits is probably directly comparable to 4:2:0 IBP MPEG at 25 megabits. On a non-static scene, they will not be directly comparable, and the longer the GOP, the less comparable they will be, motion-wise. And the shorter the GOP, the more comparable the motion will be, but the less comparable the discernible data will be.

No easy answers when it comes to MPEG -- it's a tricky beast!

[PappasArts]

Hi! Barry

Ehhh! Glad I don't have to write the code for a NLE to work with GOP. Especially 15 gop. It's amazing that the FX1 does as good as it does with a 15 gop string. It's probably at the edge of crashing with heavy motion. The long GOP is great for a distribution medium that's for sure. I am still amazed by the Mpeg codec and how much it can squeeze into a small space. Thanks for the info.........


michael






The longer the GOP, the more effective and efficient the compression is. However, other issues come into play with long GOPs -- a significant shift in scenery (i.e., a cut to a different scene, for example) can really play havoc with a long GOP. In cases like that the picture may become quite fuzzy until the next GOP comes into play.

So long and short GOPs both have their advantages. In acquisition it's generally thought that the shorter GOP, the better -- Sony's professional MPEG-IMX camera uses I-frame only, so the equivalent GOP is, well, one frame. No B or P frames are used at all. As long as you've got an adequately-fat bit pipe, it can deliver superb results -- but it's basically the same as a DV or DigiBeta type of intraframe-only compression scheme at that point.

For delivery, long-form GOP is the norm. DVDs use a GOP of, what is it, usually 15 or even 18 frames? Satellite HD broadcasts use long GOPs as well. If you have to cram a lot of data into a small data pipe, the longer the GOP, the more efficient the compression.

As to the 25mbs vs. 60mbs comparison: they're comparing MPEG to MPEG. They're comparing I-frame-only MPEG against IBP MPEG. Presumably they're also comparing 4:2:0 vs. 4:2:0, etc. In those circumstances, yes, I'm sure their 25 vs. 60 is probably right. That however doesn't bear any relevance when comparing against other compression schemes: you can't take that 60 megabits number and then compare it against MJPG or DV50 or DV100, because while they're also DCT-based compression schemes, they're *different* -- and equivalent bitrates don't equate when you're talking about dissimilar codecs. So be clear: they're talking about I-frame-only MPEG at 60mbit vs. IBP MPEG at 25 megabit. And even then, it's still not truly possible to compare, because the motion rendition of I-frame-only MPEG will be far superior to that of long-form IBP MPEG.

I guess I'd say it like this: on a static scene, 4:2:0 I-frame-only MPEG at 60 megabits is probably directly comparable to 4:2:0 IBP MPEG at 25 megabits. On a non-static scene, they will not be directly comparable, and the longer the GOP, the less comparable they will be, motion-wise. And the shorter the GOP, the more comparable the motion will be, but the less comparable the discernible data will be.

No easy answers when it comes to MPEG -- it's a tricky beast!

[Rosestar]

I'm glade you started this thread, even though it is too much like math (which I lost the abitity to do at a Pink Floyd concert a while back... pretty sure I had it with me when I went in...)

Short GOP= better handling or motion or other temporal changes, yes?

Long GOP= Better, more effiecent compression (more stuff, smaller package), Yes?


My concern about HDV is the effect of filters on the codec and how will that affect the image. It has been a while since I have done a project without a least one filter added. In most instances I am adding quit a few, 3 way color, a little gamma shift, you know.

How does this codec handle that.

[Batutta]

My early experience with HDV and filters has not been promising. I don't think it's because the image starts to degrade, I just noticed that gamma corrections and changing of saturation tend to bring out artifacts already in the image, especially macro blocking in uniform areas of color like the sky. This makes it difficult to do a film style gamma curve to hdv footage and get that coveted film look.