Does VRD have a Frames Per GOP limit? (audio frames removed)

jmc

Active member
I ask that because I'm trying to puzzle out the problem when VRD strips out thousands of audio frames.
When I see VRD "fast frame copying" slowly it is usually because it is removing audio frames.

The one problem file I checked had a 9+ second GOP.

And I've found that if I put the problem file into TMPGEnc "Smart Renderer" and run Analyze that
it is the video segment not audio that has a problem.

"Smart Renderer" can fix the file and I can continue to use VRD to edit the file with no problem.

"Smart Renderer" says that it will recode any GOP that has too many frames.
(have not been able to figure out what that frame limit is)

The video scan bar results looks like a fine tooth comb with red marked areas.
"Smart Renderer" will RECODE a few seconds of video then "Smart Render" a few seconds.

I assumed that GOPs always were consistent in size but guessing now that probably not
seeing that "Smart Renderer" recodes a hundred(s) different areas in the problem file. (which makes VRD happy)

So was just wondering if VRD's problem with the file might be the same as the "Smart Renderer" problem? (GOP frames limit?)

Thanks,
jmc
 
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musicvid

Member
Sounds like you have unrecoverable stream errors (broadcast recording?).
400 frame GOPs are not uncommon in AVC, so 9 seconds is quite within reason.
 

jmc

Active member
OH!, I again forgot to put that the files are h264.MP4s, Sorry.

Purchased VODs...so, guess it is encoding errors. Most files are fine. they all play fine.(VLC)

So no frame limits with VRD and h264.MP4s good to know.

TMPGEnc "Smart Render" probably does a lot more unlisted things.
It's wonderful at fixing problem files which I always edit with VRD.

Thanks to all.
jmc
 

Dan203

Senior Developer
Staff member
Did you check the frame rate? In most cases this is caused by variable frame rate
 

jmc

Active member
Did you check the frame rate? In most cases this is caused by variable frame rate
Find one of the problem files and you're right. 15 to 30 fps. (why do they do these things)

With a "Preload" QSF, VRD strips out thousands of audio frames and now MediaInfo says "Constant frame rate".
And VRD can now open the file and scroll. Of course the audio is chopped up.

I can't say I understand whats going on here tho.

-------------------------MediaInfo---(preQSF)---------------
Frame rate mode : Variable
Frame rate : 23.976 FPS
Minimum frame rate : 15.000 FPS
Maximum frame rate : 30.000 FPS

Thanks,
jmc
 
Last edited:

Dan203

Senior Developer
Staff member
Find one of the problem files and you're right. 15 to 30 fps. (why do they do these things)

With a "Preload" QSF, VRD strips out thousands of audio frames and now MediaInfo says "Constant frame rate".
And VRD can now open the file and scroll. Of course the audio is chopped up.

I can't say I understand whats going on here tho.

-------------------------MediaInfo---(preQSF)---------------
Frame rate mode : Variable
Frame rate : 23.976 FPS
Minimum frame rate : 15.000 FPS
Maximum frame rate : 30.000 FPS

Thanks,
jmc
VideoReDo assumes a constant frame rate, so when you process a file like this it recalculates the time stamps for each video frame to be constant duration and throws out any audio frames that don’t match up. Where as the original video may display frames for longer periods of time with multiple audio frames matched to a single video frame. If you watch the video back you'll likely notice places where the speed of the video seems to be faster than expected as well.

This is why it's such a tricky issue for us to fix. The whole core of VideoReDo is built around the assumption that videos will have a constant number of frames per second and that the audio will align to those timecodes. We could probably remux a VFR video, but doing any sort of editing or sync adjustments would basically be impossible.
 

jmc

Active member
Hmm, Good to know.
That stuff can sure be a tricky business.

In my testing...
TMPGEnc Smart Renderer can process that file one time and VRD is happy with it.
Process the original file again and VRD is not happy with that one.

Thank goodness, I'm at least one way or another finally able to edit with VRD.

Thanks,
jmc
 
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