Transcoding and release thoughts for huge bitrate avchd

rigs

I import my original AVCHD clips directly into avid at DNxHD 175 Mbps. Avid will have promblems with anything that has peaking bit rates that go over 40Mbps. With those type of files I have to transcode with SmartFFmpeg using a loseless setting, that converts the AVCHD codec to a H264 mov.

As LPowell says the higher bitrate files loose efficiencies and I believe they do not always add up to better quality, and in some cases they can create problems in your workflow. I would rather save time and disc space to have AVID import the files then add another step in the process. The less you have to transcode your original files the better.

chauncy

got it. I'll take a whack at the mainconcept stuff.
That makes it clearer.

LPowell

@chauncy
There are many Profiles and Levels of H.264 detailed in the specs, with widely varying quality and efficiency. Driftwood's 176Mbps patch produces high quality H.264 files that are inefficiently compressed at a high bitrate. If H.264 transcoding parameters are chosen properly, bitrate can be lowered without significantly degrading quality.

In Premiere CS5, sequence type will remain AVCHD 1080p23.976, regardless of which GH2 24H patch is used. You can render a transcoded file at any time before or after editing one or more clips on the timeline, depending on what makes your workflow most efficient.

For narrative film shooting, I prefer to color correct and normalize all usable footage to a consistent exposure and color palette before it's edited together. This increases the in-memory color depth of the graded video, and I think it's worthwhile to render the results in 10-bit H.264 color. To do this, I fine-tuned a custom Hi10P Level 4.1 Profile in the MainConcept Codec Suite 5.1 plugin with a 75Mbps max bitrate. This plugin provides detailed encoding parameters that are not accessible in CS5's bundled H.264 encoder.

This type of pre-production transcoding could also be done with the free x264 encoder via command line batch processing. The MainConcept Codec Suite 5.1 plugin was worth paying the licensing fee for the seamless integration it provides with Premiere CS5.

chauncy

So you're saying the value of transcoding to h264 before editing in premeire is just that it is a more efficent codec to work with. That is, there will be no difference in the quality of the edited file.

Otherwise, I'd appreciate an abbreviated work flow since what we have isn't really an avchd file.
1) what should the initial sequence setting be? 1080p avchd like usual or something else?
2) after editing, what should it be transcoded to? Is this where mainconcept is needed or
could I use a custom profile?

I mean for highest end quality. Let's pretend just as a file with no delivery type.

Thanks.

Mihuel

Thank you for your sensible answer. It gives me much to think about. I have read more about proxies to make life easier :-)
P.S. Premiere is not Cubase or ProTools and I have to learn , learn ....

LPowell

@Mihuel
While Premiere CS5.5 will decode it properly, the high AVCHD bitrate will become a performance issue once you start laying effects on the timeline. Using a faster codec and/or lower bitrate will make it more responsive. Using proxies to substitute for the 176Mbps clips is another effective option.

Mihuel

@LPowell
So, even at 176Mbits Driftwood Intra, in CS5.5 better to transcode to another codec Intra (DNxHD or Cineform) because Premiere does not deal with the correct (best) decoding AVCHD? (And I do not mean the difference between 8bits color and 10 bits...)?

LPowell

@Mihuel
The value in transcoding Driftwood's 176Mbps intra-frame patch to H.264 would be to lower its huge bitrate without degrading its image quality. CS5.5's bundled H.264 encoder isn't a good choice because, without B-frames, it cannot produce efficiently encoded AVC files. It's similar to the GH1's AVCHD encoder, which also lacks B-frames, and needs 75+ Mbps to produce its highest image quality. The GH2's B-frames enable it to produce comparable image quality at rates as low as 44Mbps.

Mihuel

@LPowell
"If you want to maintain the quality of a 176Mbps intra-frame video, transcoding to ..."
You wrote that the CS5.5 does not use B-frames but 176Mbits Drifwood not use the B-frames so whether it makes sense to transcode to another format? I am not a professional so do not be upset this question

LPowell

@sam_stickland
While the Blu-ray spec's maximum data transfer rate is 54Mbps, video bitrate is limited to only 40Mbps. Maximum GOP-size is normally one second, i.e. 30 frames for telecined movies. However, scene detection is used to dynamically insert key frames as needed. As you point out, Blu-rays are mastered with non-real-time multi-pass encoders, and produce far more efficiently compressed files than a camcorder encoder can record in real time.

@chauncy
The bundled H.264 encoder in Adobe CS5.5 does not use B-frames and is thus not very efficient. If you want to maintain the quality of a 176Mbps intra-frame video, transcoding to DNxHD (free download from Avid) or CineForm are probably your best options, unless you have a Mac and want to use ProRes. To produce high-profile H.264 transcodes with CS5.5, you need a licensed plugin like MainConcept Codec Suite 5.1, or alternatively you could process the MTS files externally with the x264 encoder.

sam_stickland

Well Blueray is spec'ed as 54.0Mbps, with - IIRC - a variable that GOP that's usually around 10? Rendering is a non-realtime encode so it can make more efficient use of the bitrate. I used a similar encoding for a short film that was shown at a local cinema last week (part of the 48 Hour Film Project) and it looked good to my amateur (but slowing improving ;) eye.

I'm curious what the low-GOP lovers on this forum think of the motion rendering of Blueray?

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