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Old November 21st, 2010, 07:16 PM   #1
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AVCHD Disc 17 Mbps limit?

My Sony NEX VG10 has 3 levels of video quality reflected as:
FX: 24Mbps (Max)
FH: 17Mbps (avg)
HQ: 9Mbps (avg)

and the manual states shooting at the FX setting will produced footage that is not compatible with AVCHD discs.........should I still shoot in the FX mode if I am going to edit the footage in FCP and export to an AVCHD disc?

My thinking was to capture the video at the cameras best setting and allow Titanuim Toast 10 to encode down to the necessary bit rate to ensure compatibility.
How would you guys handle the bit rate options?
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Old November 23rd, 2010, 10:51 AM   #2
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Originally Posted by Steve Nunez View Post
My Sony NEX VG10 has 3 levels of video quality reflected as:
FX: 24Mbps (Max)
FH: 17Mbps (avg)
HQ: 9Mbps (avg)

and the manual states shooting at the FX setting will produced footage that is not compatible with AVCHD discs.........should I still shoot in the FX mode if I am going to edit the footage in FCP and export to an AVCHD disc?

My thinking was to capture the video at the cameras best setting and allow Titanuim Toast 10 to encode down to the necessary bit rate to ensure compatibility.
How would you guys handle the bit rate options?
Although I don't have or use a Mac, I can tell you that it would be better to shoot at the lower 17 Mbps bitrate if you're going to ultimately author the video onto AVCHD DVD simply because downconverting an already lossy-compressed 21 Mbps video to a lower bitrate would have degraded the image quality so much that it would have looked noticeably worse than if you had shot this same footage at the lower bitrate to begin with. This is due to the fact that software downconversion does not use the correct alogarithm required to maintain image quality (in other words, software downconversion from lossy to lossy usually sucks). As such, my only use for 21 Mbps AVCHD footage would be if I had a full-blown Blu-ray disc to author the video on.
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Old November 24th, 2010, 03:43 PM   #3
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Randall:

In general, I would have to disagree with you. First off, most NLEs, even if rendering to the same format as the source material, will re-compress your footage anyway, so starting off with a lower-quality source usually translates directly to a lower-quality result. Since the expectation--especially for the "pro" NLEs like FCP and Premiere--is that people are going to color grade and do other things that make direct re-use of the source material impossible, most of these programs simply decode the source material, apply changes (if any), and then re-encode in whatever target format you've selected. If there are no changes to apply and the target format is the same as the source, the video is usually still decoded and re-encoded/re-compressed (needlessly), degrading the quality even where one would reasonably expect the unmodified video to pass straight through unharmed. Perhaps oddly, it's the consumer-oriented NLEs (e.g., Corel VideoStudio on Windows) that tend to do a better job in this particular scenario. Moral: Know your NLE *really well*!

Lastly, there is no such thing as a "correct algorithm to maintain image quality" during downconversion. It is, after all *down*conversion. :) The problem, as stated above, is that most NLEs don't recognize and take advantage of opportunities to directly re-use source material with a compatible output format.

Best,
Aaron
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Old November 24th, 2010, 05:21 PM   #4
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Originally Posted by Aaron Holmes View Post
Randall:

In general, I would have to disagree with you. First off, most NLEs, even if rendering to the same format as the source material, will re-compress your footage anyway, so starting off with a lower-quality source usually translates directly to a lower-quality result. Since the expectation--especially for the "pro" NLEs like FCP and Premiere--is that people are going to color grade and do other things that make direct re-use of the source material impossible, most of these programs simply decode the source material, apply changes (if any), and then re-encode in whatever target format you've selected. If there are no changes to apply and the target format is the same as the source, the video is usually still decoded and re-encoded/re-compressed (needlessly), degrading the quality even where one would reasonably expect the unmodified video to pass straight through unharmed. Perhaps oddly, it's the consumer-oriented NLEs (e.g., Corel VideoStudio on Windows) that tend to do a better job in this particular scenario. Moral: Know your NLE *really well*!

Lastly, there is no such thing as a "correct algorithm to maintain image quality" during downconversion. It is, after all *down*conversion. :) The problem, as stated above, is that most NLEs don't recognize and take advantage of opportunities to directly re-use source material with a compatible output format.

Best,
Aaron
You are correct that many NLEs - both consumer and prosumer - do re-encode and re-compress AVCHD material needlessly even if the target bitrate is exactly equal to that of the original footage. That's why to minimize this loss, if the particular NLE always re-compresses and re-encodes video even in the same format with the same bitrate I'd recommend converting AVCHD to a "less-compressed", "easier-to-edit" format such as Cineform. And in my experience the biggest-selling consumer-oriented NLE (Studio 14 HD) always re-compresses and re-encodes HD video no matter what (its smart-rendering feature only works properly with 480i standard-definition content) - and worse, Studio's downconversion is even more destructive than the ones used in most of the "Pro" NLEs. No wonder why I got relatively poor quality at relatively high bitrates from videos transcoded via Studio.

You are also correct that a "17 Mbps" AVC video as output from most NLEs will not be as good as a 17 Mbps AVC video directly from the camcorder's storage media. In the worst cases, a 21 Mbps video downconverted to 17 Mbps using typical NLE settings will result in "HD" video that looks as bad as or worse than 480i standard-definition MPEG-2 video at only 4 Mbps.

And directly copying the MTS files onto disk will not result in a playable disc without major modifications to the disc's directory structure.

Last edited by Randall Leong; November 24th, 2010 at 05:54 PM.
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Old November 24th, 2010, 05:55 PM   #5
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I'd definitely suggest giving Corel VideoStudio Pro X3 (usually somewhere between $50 and $80, depending on promotions) a look. For quick edits with my NX5, it's almost a miracle, although it doesn't yet deal well with 720p60 24Mbit/s footage, which I'd like to shoot more of. For that, I use Premiere and grudgingly suffer the losses.

VideoStudio Pro X3 will put your AVCHD on an AVCHD disc or Blu-ray virtually losslessly (I say "virtually," because the GOPs right at the cuts need to be fixed up, but the rest can pass through byte-for-byte unless you've added titles or other effects). When choosing a render format, it will even show you a little graph that indicates which portions of your video need to be recompressed and which will be left unmodified. They even have an "MPEG Optimizer" export selection that automatically picks the format that entails the least amount of recompression, and if you haven't added any titles or effects, that'll be zero.

Anyway: Highly recommended.

Regarding Blu-ray disc structure: The AVC streams on a Blu-ray disc are just M2TS files. Many free tools (e.g., tsMuxeR) can take an M2TS file and create the directory structure and indexes for you, and this too is completely lossless. If you have one big M2TS file that you want to throw on a Blu-ray, very easy to do without any re-encoding whatsoever.

Cheers,
Aaron
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Old November 24th, 2010, 06:06 PM   #6
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Originally Posted by Aaron Holmes View Post
I'd definitely suggest giving Corel VideoStudio Pro X3 (usually somewhere between $50 and $80, depending on promotions) a look. For quick edits with my NX5, it's almost a miracle, although it doesn't yet deal well with 720p60 24Mbit/s footage, which I'd like to shoot more of. For that, I use Premiere and grudgingly suffer the losses.

VideoStudio Pro X3 will put your AVCHD on an AVCHD disc or Blu-ray virtually losslessly (I say "virtually," because the GOPs right at the cuts need to be fixed up, but the rest can pass through byte-for-byte unless you've added titles or other effects). When choosing a render format, it will even show you a little graph that indicates which portions of your video need to be recompressed and which will be left unmodified. They even have an "MPEG Optimizer" export selection that automatically picks the format that entails the least amount of recompression, and if you haven't added any titles or effects, that'll be zero.

Anyway: Highly recommended.
That is one of the few that can do such "smart rendering" of AVCHD files close to "correctly". The latest updated version of the software that comes with the camcorder can also do this but is otherwise limited. And if one uses such software do not shoot at the FX mode unless the end result will be on full-blown Blu-ray (BD-R) disc. If the end result will be on AVCHD DVD using less-expensive, lower-capacity DVD media stick with the FH mode. Otherwise, shooting at FX and then downconverting will force the same destructive re-compression and re-encoding described above.
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Old November 25th, 2010, 07:34 AM   #7
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Agreed.

Which leads to one last piece of advice (or a question) for Steve:

Have you thought about buying a Blu-ray burner? You've got a $2000 camcorder, so hobbling it just so that you can get away with using a less-compatible DVD-based solution at a time when Blu-ray burners are under $100 doesn't make a lot of sense to me. And particularly if, as discussed above, your NLE of choice can't "smart render" your unmodified AVCHD, it would be nice to be able to render your project at 35-40Mbit/s (as allowed on a proper Blu-ray disc) to partially compensate for the quality penalty inherent to re-encoding.

Best,
Aaron
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Old November 26th, 2010, 08:23 PM   #8
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Agreed.

Which leads to one last piece of advice (or a question) for Steve:

Have you thought about buying a Blu-ray burner? You've got a $2000 camcorder, so hobbling it just so that you can get away with using a less-compatible DVD-based solution at a time when Blu-ray burners are under $100 doesn't make a lot of sense to me. And particularly if, as discussed above, your NLE of choice can't "smart render" your unmodified AVCHD, it would be nice to be able to render your project at 35-40Mbit/s (as allowed on a proper Blu-ray disc) to partially compensate for the quality penalty inherent to re-encoding.

Best,
Aaron
Actually, Blu-ray burners still cost $150 to $200. Ther Blu-ray drives that cost less than $100 are just DVD burners that happen to read Blu-ray discs.
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