XF605 Intra-frame vs Long GOP recording externally

[NickMDal]

Hi. I'm using a Canon XF605 recording to a Ninja Inferno in pro-res.

I'd like to shoot 60 fps in 4K to enable smooth slo-mo. That is only possible if I select long GOP vs intra-frame. Connecting a recorder does not change this.

For editing and quality-wise, is it moot when recording pro-res? I am confused since Canon's HDMI output isn't raw or normally compressed.

[NickMDal]

On DVInfo, someone just pointed out that long GOP and intra-frame only relate to internal recording (which makes sense).  So it seems to be moot. 

What does the HDMI output send?  It is a mystery.  I would guess individual uncompressed frames, which is not raw.  I wonder what it is!

So... One can shoot full quality 1080P at 120fps to an external monitor.  That is good news!

Side note...  Only the R3 can shoot at a higher framerate - 240fps.  Too bad it has so many other expensive features!

[rs-eos]

The manual should at least outline the bit-depth and chroma-subsampling that would be sent out the HDMI port (e.g. 8-bit 4:2:2 or 10-bit 4:2:2).

In terms of what type of signal it would be, it should be uncompressed.   The HDMI spec should have the details.

[NickMDal]

Well it's not so straightforward.  XF605 does not send slow motion to a recorder.  The "shooting" framerate is not recognized.

So, the only workaroud is to record to the SD card 1080P 422 10 bit Long GOP.  They play it back to the recorder, which will record the 30/120 footage 1/4 of 120fps.  The Long GOP artifact is present.

The camera cannot shoot at a native 120fps framerate.  So no way to record normally and then reset it to 30 in post.

[rs-eos]

The manual is confusing in that it's not showing any framerates for 4K output.   For HD at 1080p, I only see framerates maxing out at 59.94i (so that seems to thus max out at 29.97P).   A lower resolution of 720p could then output 59.94P.

Having said all that, you wouldn't be able to output 120 fps over HDMI at all.

Instead of recording that footage internally and then sending out to an external recorder, why not just import the original footage and transcode as needed in your non-linear editor?

[NickMDal]

I don't understand the transcode recommendation.  Are you saying to take the recorder out of the loop?

I lose the editing codec pro-res.  We shoot with 3 timecoded cameras so editing compressed video directly would bog down the editing process.  I would also lose the 7" bright display.  All shooting is outdoors.  Fast moving insects in bright sun.  The LCD would be difficult to rely on.

I don't know if Davinci Resolve would recognize the defined shooting rate vs the playback framerate.  I know how to reset the playback framerate in DR.  Also not sure how to transcode to an intermediate codec.  I can only use the pro-res codec by recorder since I am in windows.  I don't have a license for Avid's DNx codecs.

[rs-eos · Accepted solution]

I'm confused.  If you need to record high frame rate footage, then as you found, you'd need to record to internal media.   You had then stated that you were playing back that footage and using the recorder to record.   Presumably you then take ProRes footage from the recorder and injest that.

I was recommending bypassing that middle step.  e.g. with Final Cut Pro, you can always create "optimized media" which would be ProRes.

[NickMDal]

Okay I just experimented in DR and found it does transcode to DNxHR HQX.  Sorry for my confusion since in the proxy media format, prores is not listed.  Since I can't use DNx in the recorder without paying extra for the license, I assumed DR would not transcode to that format.  Happily I'm wrong!

So I assumed I was limited to the prores output of the recorder.  Not so!  Thanks for guiding me here.

So for recording 120fps, the monitor is just a monitor.  Since the camera output is 1080p, the transcode is about as time consuming as my play/record method and so vastly better.

By your approach, I end up with LOG 1080p, 120fps, 10 bit 422 footage converted to DNx. 🙂

One last question if you don't mind.  MP4 does not list a compression method (like long-GOP or intra-frame), but it has the same bitrate as XF-AVC.  Which of the two XF compression methods is it more like?

[rs-eos]

Nice! Glad you're able to maximize the quality of the 120 fps footage.

In terms of what MP4 compression would be closest to, my guess would be XF-AVC Long GOP.   It gets tricky when comparing just bitrates since newer codecs often have higher quality at the same bitrate as older codecs.