FS7: H.264 videobit rate for editing

J

jpham

Well-known member
Since I start shooting a lot of XAVC-I at 59.95fps (600mbps), what's an efficient H.264 videobitrate
to edit further ?
 
600 Mbps = 75 MB/s

But why are you transcoding to h264 to edit? It's horribly inefficient to edit with and outs a large strain on most systems.
 
I'm shocked to discover via Google that H.264 actually has an intra-frame variant. I do want to point out, though, that H.264 is almost always interframe. Most compressors that create H.264 won't even have a way to create the intra-frame variety. Also, I'm not sure how the edit performance of the intra-frame H.264 would perform, I do know that performance with the inter-frame H.264 is absolutely horrible.
 
ChristopherA said:
Also, I'm not sure how the edit performance of the intra-frame H.264 would perform
Click to expand...
Intra frame H.264 uncompresses just fine and is comparable to other codecs.

The issue with slow editing is not the efficiency of decompressing an I-frame but has to do with inter frame compression. Inter frame compressed H.264 plays forward just fine but if you are scrubbing or positioning the play head the decompressor needs to calculate the current frame from other frames which is time consuming and causes the slowdown.

I believe the bad reputation of H.264 as a codec is generally unwarranted. The technology is actually similar to ProRes as both use a DCT form of compression, this unlike for instance Cineform which uses a completely different technology.

H.264 is actually more efficient in compressing video than for instance ProRes or DNxHD because it allows inter frame compression, you get the same quality with a lower bitrate. However inter frame compression is not suitable for editing.

But intra frame H.264 works fine in an NLE andgives comparable results to ProRes.

Furthermore H.264 also supports high bitrates and various chroma subsamplings up to 4:4:4 and you can encode all the way up to lossless.

Unfortunately though a lot of applications can only use or generate H.264 8bit inter frame 4:2:0 formats.
 
Last edited:
Cary—I'm curious, are you speaking from actual experience with the format or is this based on theoretical published specs. If you have experience with H.264 Intra, how are you generating that file?
 
Back to original question - why not edit the XAVC files? Or are you looking for an "intermediate" codec - meaning maybe you do some editing, add some effects, then want to export that and then do more editing/effects on the exported file?

I don't know if you are on PC or Mac. On Mac, just use ProRes. On PC - wait, what NLE do you use? Adobe Premiere CC has Cineform (.mov) and Avid DNxHD (.mxf) codecs included and either will work well as an intermediate.

Please explain your intended workflow with more detail, question is not clear

Thanks


Jeff
 
actually I edit the whole thing in XAVC-I, then export to H.264. The final step is to customize certain stuff to some customer. What I notice is that the video is very blocky once export to H.264.
 
Yes that's pretty much the nature of h264.

Is it not possible to render out a master pro res or dnxhd sequence and have that as the one you do further customisation on before exporting a final h264?
 
Except nobody does that (aside form you) and there are zero advantages to doing that over working with native rushes or a pro res or dnxhd master.
 
Then what do you ship to your customer ? Customer can only see it in H.264, the FS7 only output XAVC-I
I don't think they want to see it in PRORES 4K at 60fps - the huge PRORES is way too big.
Heck on our 36 cores machine 4K 60fps really stress the machine, you think an I7 can do it better?
 
Yes you've said that before but not explained why you are transcoding to that to edit over and above cutting with the original rushes or just offlining via proxies. What is it you're gaining by having this stage of transcoding?
 
You must log in or register to reply here.
Back
Top