Bitrate advice on ingest

[sebrame]

I'm transcoding AVCHD (24Mb/s) footage to Cineform.  Is there a picture quality reason to transcode to a higher bitrate than the source files?

[R Neil Haugen]

You don't want to go lower for either bit-rate or depth, but about the same or slightly higher Mbps and same bit-depth should work perfectly for most media. And the Cineform will sure playback/edit beautifully. Now ... if the Mbps of the original media is highly compressed ... you might be going to a larger Mbps file by a fair amount. Some DSLR's, especially in H.264-4k work, most drones & M4/3 cams might need a bit more Mbps to maintain the full quality of the original file.

Neil

[sebrame]

My source files are generally H.264 in either MTS or MOV wrappers, 24Mb/s 1080P 23.97. I wish there was a chart available that would show what the 'sweet spot' bitrate for transcoding different types of footage is, or at least a best guess at the law of diminishing returns.

[Warren Heaton]

For Cineform, you'd just pick "Cineform 4" and leave it at that (and maybe cross your fingers that you have enough disk space to store the transcoded media).

For professional CODECs for editing, the bit rates are mostly fixed based on the intended use of the footage (High Resolution, Low Resolution, etc.) and determined by the CODEC.  It's delivery CODECs like MPEG2 and H264 that allow the user to set bit rates (usually a target bit rate and a maximum bit rate).

Apple and AVID post detailed information about their CODECs.

• Here's a link to the Apple ProRes white paper: https://images.apple.com/final-cut-pro/docs/Apple_ProRes_White_Paper.pdf
• Here's a link to the AVID DNxHR white paper: https://www.avid.com/static/resources/US/documents/dnxhd.pdf

Digital Rebellion has a great online storage calculator:

Video Space Calculator - Digital Rebellion

[Jim_Simon]

Cineform is a Constant Quality codec, which means it doesn't target a bitrate, but a quality level.  It will use as many bits as it needs to hit the target quality.  This is part of what makes Cineform such an excellent codec.

For proxy work, a Quality setting of 1 or 2 is plenty.  I transcode my RAW media to Cineform files with Quality 3 for final editing because that editor likes small files.  Though for my own stuff, I always use Quality 4.  (5 is too high and best reserved for effects work only.)

[sebrame]

So what I'm getting from this is that it's fairly subjective. Our work is hardly 'cinematic' in nature, but usually corporate training, PR and marketing with a lot of talking heads(usually green screened). And while drive space is certainly a consideration, it's rather cheap these days - not a big deal to tack on an additional HD to the RAID if need be. Coming originally from an Avid world, I'd opted for DNxHD as my mezzanine codec, but the 'Constant Quality' aspect of Cineform is what made me want to switch. I just wish there was a less subjective way to tell if I'm overdoing the quality/bitrate in a transcode. I've been doing tests of all Cineform and Avid DNxHD presets the past few days, and I swear that I can't visually tell the difference between Cineform 2, 3 and 4 or Avid HQ, SQ or LB. Perhaps the biggest difference would be if I did a lot of grading, which I generally don't.

[Warren Heaton]

Sebrame:

For "mezzanine" or editing CODECs it's all about compression generation loss.  That is, does the picture quality diminish if you transcode the footage. 

Read the Apple ProRes white paper that I linked to and pay close attention to the section on Peak Signal Noise Ratio (PSNR). 

Does your workflow require the assurance that a 10th generation clip will look as good as a 1st generation clip?  Or that a 100th generation clip look as good as a 10th generation clip?  It doesn't sound like it does.  If you were on Mac, I'd recommend Apple ProRes 422 LT.  Since you're on Windows, Cineform 4.  However, you could opt to not transcode your camera originals at all.  As long as you're happy with the image quality of the video that you publish, you're good to go.  Important note:  don't underestimate the importance of production value whether you're doing a 30 second social media piece or producing what you hope to be the next Oscar contender. 

An important take away from your observations is that you can't tell how well a CODEC will hold up to being recompressed with the naked eye.

In a perfect world, all of our video would have no compression. 

Have you researched color depth yet?

-Warren

[sebrame]

"Does your workflow require the assurance that a 10th generation clip will look as good as a 1st generation clip?"

Certainly not, and I'm not even sure I understand why such a workflow would be necessary. Maybe it's just that I've not experienced cinematic workflows, requiring that encodes get passed from system to system. My output gets encoded once from the timeline, then once again on whatever platform I post to.

"However, you could opt to not transcode your camera originals at all."

As I've been doing since CS3, but in order to upgrade to CC2018(at least until I decide to upgrade to Windows 10), I have to begin transcoding to a mezzanine again due to my camera's audio codec being AC3. Plus, since my current machine is not very 'beefy', I think I might rather enjoy the smoothness of editing Cineform or Avid codecs again.

"An important take away from your observations is that you can't tell how well a CODEC will hold up to being recompressed with the naked eye."

I realize this. That's why I'm testing to see what the visuals are AFTER recompression - in this instance, YouTube's recompression.

"In a perfect world, all of our video would have no compression."

And I'd still be in my 20's, not my 60's.

[Warren Heaton]

There's a general rule in filmmaking that comes from the days of having your picture on film negative: Your film negative must always be treated like it's worth more than gold because without it you're taking nothing to the bank.  Now that we've transitioned into digital images, the same rule applies to your camera originals.  One could make the counter argument that as long as one is telling a strong story an audience is willing to forgive poor picture quality, but that's very much an exception to the rule. There's also having the confidence that while the picture is under your control that it's always a high quality image.

If you just go with Cineform 3 or 4 or ProRes LT, you can forget about the rest and focus on everything else that needs attention in visual storytelling.  When you're ready to upload to YouTube, a 1st generation clip at the YouTube or Vimeo H264 presets in PR and AME will hold up just fine.

It's unfortunate that someone even made a camera that records audio to AC3.  It's just as unfortunate that someone made cameras that record to long-gop MPEG2. 

[Jim_Simon]

I wish more camera companies would adopt Blackmagic's design philosophy.  Nary a camera in sight using MPEG anything.  It's RAW or ProRes, period.  And audio has only one option, 24 bit 48 kHz Uncompressed.

[Warren Heaton]

I second that!

[Jim_Simon]

Run a test of the green screen work in Cineform 3 and 4.  Blow it up to 400%.  If you can't see a difference under those conditions, use 3.  If you can, use 4.