This is basic question reflecting my state of learning about AVCHD camera and MC6. I am able to use both camera and MC6 at beginner level, but would like to understand some basics.

Literature for my Panasonic AG-HMC40 AVCHD says it records at 21 to 24 Megabit per second, 4:2:0 8 bit color sampling depth when recording 1080i (60 fields/sec).  From what I read DNxHD145 is recommended editing transcode for this AVCHD "rate" and MC6 seems to automatically select this setting when I transcode my video.  However, I have also read you should somewhat match data rates of NLE to camera data rates. 

However, when I read Avid documentation it says DNxHD145 data rate for 1920 by 1080 1080i 8 bit is 145 Mbps.  It seems there must be some different measuring protocol between "data rates" reported for camera recording (21 to 24 Mbps in my case) and "data rates" reported for NLE (145 Mbps for DNxHD145)or I would just use DNxHD36 data rate for my HD 24 Mbps camera data rate?

Edited footage of my 1080i recording using DNxHD145 transcode looks great to my eye, but I always wonder if it would look better if I used DNxHD220 (Avid documentation says DNxHD220 gives "highest quality image and color space for 10 bit sources so I guess "my" 8 bit color sampling depth would not benefit here?).

DNxHD220 will probably be overkill for what you will be doing with AVCHD video.  We use DNxHD145 because we don't get any imporvement in our video for the extra disk space that 220 would take up.

As to the matching data rate question, I am thinking you may be confusing matching FRAME rates between camera and project as opposed to matching DATA rates.  Data rates are not important to match.  Data rates are specific to codec/compression being used for the video, e.g. AVCHD, MPEG2, DNxHD.  Those all use different ranges of DATA rates.

FRAME rates, however, are a different beast altogether.  If you shoot progressive (24p, etc), you edit progressive.  If you shoot interlaced (50i, 60i, 29.97, 59.94), you edit interlaced with that frame rate.

You should be able to find something in the MC help file that gives you a table of frame rates that are compatible with each other.  That would make a good starting point.  Then experiment.

Ben, thankyou for sharing your practical experience and I am going to stick with DNxHD145 as the best practical advice.  One question, if I ever get my wish for a projector beaming onto a 6 by 8 foot screen, would the DNxHD220 improve resolution vs DNxHD145?

On my part the theory may need more exploring when I have some spare time (I tend to waste too much time on some of the more esoteric theory).  Thank you for making sure I understand Frame rates for editing, but Avid sometimes seems to be using Frame rates and Data rates in a different context.  For instance In an Avid document  about the wonders of their DNxHD codec I read for Avid DNxHD 220x quoting " For highest quality image and color space for 10 bit sources. Data rate is dependent on frame rate. For example, 220 Mbps is the data rate for 1920X1080 interlace sources (60 fields)" end quote.

denniscasey:

Thank you for making sure I understand Frame rates for editing, but Avid sometimes seems to be using Frame rates and Data rates in a different context.  For instance In an Avid document  about the wonders of their DNxHD codec I read for Avid DNxHD 220x quoting " For highest quality image and color space for 10 bit sources. Data rate is dependent on frame rate. For example, 220 Mbps is the data rate for 1920X1080 interlace sources (60 fields)" end quote.

 

Nope.  they are not using them in a different context.  The frame rate combined with screen resolution helps to determine the data rate.  The more pixels you have to process, the more data has to flow.  And BTW, we edit DNxHD145 for our 1920x1080i/59.94 projects.  1080i projects can use DNxHD145/220/220x as well as DVCProHD/and some XDCamHD resolutions.  720p projects give other DNxHD data rate options (I don't remember them all as all our infrastucture adn distribution is built around 1080i.  BTW, they did say "For HIGHEST quality".  there is a difference between HIGHEST quality and highest REASONABLe quality.

IMO, if you don't have a really high quality capture, such as a high resolution RED camera or something that shoots in a 4:4:4 color space, DNxHD220 is wasted disc space.  You also have to have a really good drive subsystem to be able to crank the volume of data that has to flow at the higher data rate.

For big screens, it's more about screen resolution.  Higher data rates at the larger screen resolutions will equate to better pictures, but there is a point of diminshing returns that only experience can determine for you.

If you have a high performance drive array and REALLY fast connection to it and gobs of space to use, by all means feel free to use 220 (8bit) or 220x(10bit).  I think it will be worth your while to experiment with footage using the different data rates to see how much difference you can see vs the drive space you will use vs the performance of playback of multilayered timelines with effects.

It's all a balancing act. :)

Ben, excellent points and thank you for explaining this. It is indeed a balancing act-- in process engineering we talk about bottlenecks to manufacturing speed--does no good to increase output of machine A by 5 times if next machine downstream in process can only process input 3 times as fast. 

And I will do some experimenting, just very helpful to understand what to expect or look for. Thanks again, Dennis

One thing to consider.  The camera is using one compression technology.  Avid (DNX) is using a different one.  Any time you go from one compression tech to another, there will be loss.  So it can be argued that you do not want to compress to much on any step that YOU have control over.

When given the oportunity and presented with footage from a camera like the Canon 5D, I will import it into the system as UNCOMPRESSED!!!  The Canon's codec is so crappy I do not want any more damage done. (Green screen for example or something that needs severe color correction.)

Just another perspective.

Jef

jef:

One thing to consider.  The camera is using one compression technology.  Avid (DNX) is using a different one.  Any time you go from one compression tech to another, there will be loss.  So it can be argued that you do not want to compress to much on any step that YOU have control over.

When given the oportunity and presented with footage from a camera like the Canon 5D, I will import it into the system as UNCOMPRESSED!!!  The Canon's codec is so crappy I do not want any more damage done. (Green screen for example or something that needs severe color correction.)

Just another perspective.

Jef, as relative novice I appreciate hearing about things to consider in editing flow.  My current work flow is AMA link, transcode to DNxHD145 and put transcoded clips on timeline.  As experiment I did AMA link to five short clips (Panasonic AG HMC40 AVCHD 1080i) and put them directly on timeline without DNxHD transcode. Added Stabilize effect  to one clip and played back full screen best quality with no stuttering. Only five short clips (total time 2 minutes) and no layers, but computer handled ok. I read don't mix AMA linked clips and DNxHD clips on timeline so will be one or the other.  Editing "directly" in AMA linked clips would save some time although DNxHD145 transcoding goes really fast in my machine.

So here are the questions keeping in mind Ben's "it's all a balancing act" point (essentially what are tradeoffs if I edit directly AMA linked clips):

1. Will reducing compression "steps" by directly editing AMA linked clips vs adding step of transcoding to DNxHD provide noticeably (recognizing that could be difficult to quantify) better quality output?

2. If so, what are tradeoffs in terms of MC6 speed in editing and will I ultimately need to transcode timeline anyhow in order to output to Blu-ray (my output mode)?  In back of my mind I think I read something about problems you can run into if you directly edit AVCHD AMA linked clips in MC5 and maybe MC6 "fixed" those issues??

Appreciate patience and help bringing me up to speed, Dennis

 

 

Hi Dennis,

I think the issues raised about editing AVCHD media via AMA were that AVCHD is a highly compressed format and takes a lot of CPU horsepower to process.  That means a simple cuts/dissolves timeline will likely do well.  But a more complex timeline using multiple effects and/or multiple video layers may have trouble playing back.

AMA is also not indexed the way imported and transcoded media is.  Which means it can get lost more easily.  Which as I recall, has been another AMA issue that I have seen pop up from time to time on the forums.

The other caveat that I keep forgetting is you cannot export a Quicktime Reference movie with AMA clips.  You will have to export a Quicktime movie (self-contained) or mixdown or transcode the AMA clips to AVID Media.  When and where to spend time with transcode/import is all part ot he workflow evaluation.  Where do you spend time to save time?

denniscasey:

In back of my mind I think I read something about problems you can run into if you directly edit AVCHD AMA linked clips in MC5 and maybe MC6 "fixed" those issues??

Appreciate patience and help bringing me up to speed, Dennis

 

Not sure where you read that you could AMA to AVCHD in MC5.  MC6 is the version that introduced the AMA plugin for AVCHD.  You have to Import AVCHD in MC5, which results in a transcode upon import.

Cheers,

ben

Hi Ben,

Thank you for continuing to help me understand practical applications of "theory" as I continue to balance various aspects of the MC6 teeter totter. I am still learning a lot, but I thought it probably would be more a matter of at what point in process would transcoding of one sort or another have to take place if I edited AVCHD.

And good point about "where to spend time to save time."  If AVCHD bogs machine down such that editing process takes longer then I am better off to AMA link a bunch of  AVCHD clips at beginning and do something else while machine takes time to transcode all of them.

This is off topic, but actually I have noticed occasions where I have AMA linked maybe 10 AVCHD clips at once and when I tried transcoding all 10 at once I would get an error (forget now what error message was).  If I then transcoded same clips but individually they all transcoded ok.  Any idea what is going on?  That is one reason I have been nervous about transcoding an entire card at one time.  I should mention almost always I am dealing with many short clips (anywhere from 10 seconds to maybe two minutes) and not long scenes such as interviews .  Accordingly, I can have 100 clips or more of 1080i shots on a 16GB card. 

denniscasey:

This is off topic, but actually I have noticed occasions where I have AMA linked maybe 10 AVCHD clips at once and when I tried transcoding all 10 at once I would get an error (forget now what error message was).  If I then transcoded same clips but individually they all transcoded ok.  Any idea what is going on? 

Actually, that is not as off topic as you may think.  I do recall seeing a thread about that now that you mention it.  I don't recall what the fix (or workaround) was, if there was one.  Are you using the latest MC6 version?  MC 6.0.1?

Ben Wilson:

  I do recall seeing a thread about that now that you mention it.  I don't recall what the fix (or workaround) was, if there was one.

One workaround that I was reminded of while poiking around on the Cow (creativecow.net) is using Mpeg Streamclip or Handbrake.  Not sure if WinFF or FFMBC (a broadcast variant of FFMPEG) would work to transcode before import into AVID.  All worthy pieces to evaluate for workflow.

ben

Ben, I am using MC6.0.1. I have used MPEG Streamclip in past to transcode Quicktime footage to AVI that I could handle on Avid /Pinnacle Liquid. 

Have there been bug reports about the DNxHD transcoder inside MC6 or 6.0.1 when transcoding many AVCHD clips at one time?

In which case, just to confirm I understand your comment,  the workaround would be to use a 3rd party transcoder (which I guess could include Sorenson Squeeze 8 that came with MC download) to transcode AVCHD to DNxHD if dealing with many clips at once??  At one time I think I read something about Avid using a proprietary transcode method for DNxHD so it went faster than 3rd party transcode to DNxHD??  But of course if there are problems it is no longer faster.  Regards, Dennis

I'm not sure what the problems actually were with doing multiple transcodes of AMA linked AVCHD.  I didn't follow those threads as closely as I probably should have.  I tried to find them today and seemed to find a few threads that may have been related but didn't stand out to me as what I had seen.

Some of the workarounds were to transcode the .mts files using MPEG Streamclip or some other 3rd party software.  One of the producers I support uses a product from Aunsoft to convert his .mts files.

You might try searching using you error message or some portion of the error message here, on the knowledgebase, and Creative Cow.  You may find an answer, or at least know that you are not alone! :)

As far as "methods to transcode" are concerned, that gets into coding.  I'm not a code-monkey, just a systems integrator and user.  :)

Good Luck!

And as I went back out to the forum main page I found this

http://community.avid.com/forums/t/108325.aspx

Maybe that could give you a clue?

Ben, thank you for good information and pointers.  Regards, Dennis

You are most certainly welcome.  I just hope I was a help in getting you started in the right direction on the learning adventure of AVID!

I myself have found many valuable insights and helpful information on this forum.  I feel as I owe the community something for the help I have received.

Cheers,