Audio waverform display inconsistant

MrVideo

Active member
Beta 468.

I've been seeing this for a while, with lots of files, actually every file that I edit.

I have the audio display waverform display during on and the zoom is at the highest resolution.

Here is the problem. I manually look for commercial breaks, as I want to edit then personally, and I can do it much faster than VRD. For this example, I am sitting at 16:02.16. The faded audio appears to end at 16:02.28. But, if I move one frame to the right, i.e., now at 16:02.17, the audio that was still fading to the right, now ends at 16:02.05. All of a sudden the audio is done 12 frames before the current location, not 12 frames after the location.

This happens a lot. Single step through the video and the audio jumps all over the place. I don't know for sure if I'm really at the right place or not.

Also, I've see audio consistantly 3-4 frames off. A promo or commercial will appear (video) and the audio is leading it by 3-4 frames, which I know is impossible, as that is not the way promos and commercials are edited.

Using the audio to help with editing is very important, but I am beginning to doubt what I am seeing.

Any idea as to what is going on?
 

phd

Super Moderator
If I understand your question correctly, the audio display is a relative scale based upon your current location in the file and not an absolute scale that is consistent throughout the file.
 

MrVideo

Active member
phd said:
If I understand your question correctly, the audio display is a relative scale based upon your current location in the file and not an absolute scale that is consistent throughout the file.
I have no idea what you are trying to say here.

Please reread my post and then come back to here........

OK, when the thumbnail view is zoomed all the way in, I believe the frame count goes about 14 frames to the left and right of center. I can't find out for sure, as the computer is busy capturing. The exact window size is not important, other than it is at maximum zoom.

As indicated in my first post, at the end of a scene, where it goes to black and the audio fades out, one can see the audio fading. When I can see the end of the fade, it is 12 frames to the right of center. Move one more frame to the right and all of a sudden the audio fade is 12 frames to the left of center. It jumped 24 frames. Under no circumstances was I able to get the end of the fade to appear in the center of the thumbnail display area.

This doesn't happen all the time, but it happens way too often. I can never be sure if I found the right spot.
 
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Danr

Administrator
Staff member
Just checked it out here on some test file, and the audio fade displays perfectly. Move one frame left or right and the fade moves correctly.

I guess we are going to need a file upload on this.
 

MrVideo

Active member
DanR said:
Just checked it out here on some test file, and the audio fade displays perfectly. Move one frame left or right and the fade moves correctly.
As mentioned, it is inconsistant. I can do file A where it happens in locations and I can edit file B where it doesn't happen at all.

I guess we are going to need a file upload on this.
When it happens again, I'll trim a section and see if the problem stays there. If it doesn't, I'll have to ship off a DVD with the complete file.

I'll even do some screen grabs to illustrate the problem.
 

laserfan

New member
I have noticed anomalies in the audio, both re: the waveform display and the audible itself:

1. The waveform sometimes "jumps" unexpectedly when moving just a frame or two in one direction or the other

2. When playing-back to test a cut, a "piece of audio" i.e. an audible click or snippet from the last playback is heard despite that it's not actually in the join.

Note my editing is to remove commercials from broadcast HDTV--these breaks are often abrupt of course as local stations cut to commercials, or join the program "slightly in progress"! I have learned to live with VRD's oddities, though it slows me down of course. Fading to commercials, I usually listen closely to the "cranked" audio & then pause the program after the last note/beat/echo. I then step using I-frames to find a perfectly flat waveform. Sometimes I have to trust my ears and make a cut where the waveform is not flat. Other times I find one of those unexpected "jumps" in the waveform and then go back P or B frames at a time until the jump disappears.

With experience I've learned to trust my ears over the waveform, and 99.9% of my cuts are perfect.

I just recently discovered that the .vprj is a readable file, and upon completion of my edit I use the "cut times" found in there, along with my favorite PC player (Elecard MPEG Player), and play-across every cut to verify that it's good, or at least as good as it can be given the glitches that result from local stations mangling the breaks. This is a great find; I am going to use this method every edit from now on. I'm also going to retain the vprj files from now on cuz that's the kind of person I am (anal as can be).

It would be nicer to have "waveform perfection" but I don't know whether this is possible?
 

litz

New member
laserfan - what you are seeing are cuts in the ac3 stream ... VRD kinda projects ahead and behind ... so you see what it *thinks* should come ahead - then the AC3 stream changes @ the ad break and you get a jump.

I see this all the time with WSB's HD signal here in Atlanta - you get to a commercial break in LOST and it fades out ... then all of a sudden, your waveform jumps and it fades out again.

What's happening is they're cutting to a 2.0 ac3 for the commerical break - and you're catching the tail end of the fadeout from the analog transmission of the show, as it trails the DTV transmission by a few seconds.

I've also noticed that when their switcher switches, the ac3 switches about 3-4 frames before the video actually switches; I guess it's just a function of the software they use.

I don't think there's any way around this, since it's an artifact of an imperfect ac3 stream ... what I wish is that there was a way for VRD to show breaks like this with a RED vertical bar, or a some other flashy something-or-another to make finding the edits for ad breaks much easier ... or a "jump to audio cut" shortcut key ... :)

I can provide any examples wished, to show exactly what I mean, if it's requested ...

- litz
 

Danr

Administrator
Staff member
what I wish is that there was a way for VRD to show breaks like this with a RED vertical bar, or a some other flashy something-or-another to make finding the edits for ad breaks much easier ... or a "jump to audio cut" shortcut key ... :)
Litz, If I remember correctlly we started working on this by storing the # of source channels in our internal arrays. Even though the audio was switching between 2 and 5.1, it was actually all broadcast as 5.1 so by the time we muxed it down the 2 channels we couldn't tell where the break was.
 

MrVideo

Active member
litz said:
laserfan - what you are seeing are cuts in the ac3 stream ... VRD kinda projects ahead and behind ... so you see what it *thinks* should come ahead - then the AC3 stream changes @ the ad break and you get a jump.
BZZZZZT!!! Thanks for playing.

First off I do not see how a program can display a waveform pattern as to how it thinks it will look like. DanR will have to talk about this.

Please reread my postings about the horizontal audio jump in the display.

Secondly I can shoot your network to local break causing the problem full of holes. How can I do that you ask? The recordings I have are 100% network (please don't ask how that can be). The only network I record off air is Fox (very seldom NBC). I see the problem with four network feeds, which has the same audio stream throughout.

The only pattern that I've noticed is that when it happens (just thought of it now) there is a few seconds of silence after the fade. When the audio display jumps 24 frames from right to left, all of the audio on the right is silent. The jump also only happens if the video is black.

I've never noticed a problem when there is continual audio that can be displayed in the thumbnail window.

I've also never seen it have a problem when sliding in new audio on the right, with silence in the thumbnail display, until the new audio comes into view.
 

MrVideo

Active member
laserfan said:
1. The waveform sometimes "jumps" unexpectedly when moving just a frame or two in one direction or the other
I knew I wasn't nuts. :)

2. When playing-back to test a cut, a "piece of audio" i.e. an audible click or snippet from the last playback is heard despite that it's not actually in the join.
Ya, it appears that VRD isn't flushing the buffer before starting to play, after being stopped and moved to a new location. It is fine if you stop and then restart without changing location.

With experience I've learned to trust my ears over the waveform, and 99.9% of my cuts are perfect.
I've actually had excellent results with the thumbnail display and what it shows for audio. I've yet to notice a problem. Doesn't mean there isn't one, as I don't do a 100% check of the edits.

I just recently discovered that the .vprj is a readable file, and upon completion of my edit I use the "cut times" found in there, along with my favorite PC player (Elecard MPEG Player), and play-across every cut to verify that it's good, or at least as good as it can be given the glitches that result from local stations mangling the breaks. This is a great find; I am going to use this method every edit from now on. I'm also going to retain the vprj files from now on cuz that's the kind of person I am (anal as can be).
Huh? There appear to be some steps missing from your description. I have no idea what Elecard MPEG Player is and how knowing the edit locations from the project file help you play the edited locations. Are you playing the edited file?

Yep, some station master control operators need training. It would also help if the networks would return to promos from local breaks, 'cause then you don't care. Fox does that most of the time, not 100% of the time.
 
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DrP

Member
I've noticed what you are talking about, but I put it down to the dynamic scaling of the audio level indicator, not so much it jumping around in time. I guess it comes down to what frame VR samples to determine the relative level of the audio display.
 

laserfan

New member
MrVideo said:
Huh? There appear to be some steps missing from your description...
Yes I'm playing-back the edited file. Any player lets you easily track to a time point in the program, and the vprj info identifies these.
 
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litz

New member

MrVideo

Active member
litz said:
That's what I mean by "audio jump" ... the spot the waveform jumps is the point where the TV station has switched ac3 audio streams from the network show to the commercials.

It would be real nice if there was a way to mark that kind of jump to make it easier to find ...
Unfortunately I'm not going to be able to look at the TS clip until much later tonight. The computer is busy doing a recording.

But, the audio JPEGs have me worried. Unless the station always screws up, the switch from network to local , or vice versa, should alway occur during silence. Your sample has audio playing when the switch occurs.

At that point, the images will give you the cluie as to where the edit needs to take place, because there will be a drastic visual change.

Whenever I've had an issue with editing the local Fox affiliate material, the visual queues are supplimented with audio queues.

That said, it would be nice if the Ctrl-L option would show the user the format of the audio that the time location. If it only pulls it from the start of the file, that is wrong, since it can contain both DD5.1 and DD2.0, as you have so discovered.
 

Danr

Administrator
Staff member
litz said:
Okay, I made a small .ts clip ...

http://terminus.litz.org/videoredo/audioclip.ts

compare

http://terminus.litz.org/videoredo/audio1.jpg

to

http://terminus.litz.org/videoredo/audio2.jpg

That's what I mean by "audio jump" ... the spot the waveform jumps is the point where the TV station has switched ac3 audio streams from the network show to the commercials.

It would be real nice if there was a way to mark that kind of jump to make it easier to find ...

- litz
Thanks for the clip. The next build will tighten up the calculation a bit so that the jumps are less obvious. In the present version quite a few "off-screen" audio frames were being involved in the calculation to determine the min and max. This is what caused the line shape to jump.
 

litz

New member
Was what I was seeing an actual break between ac3 streams or something else?

What do you mean by "off-screen audio frames" ?

Just wondering ...

- litz
 

Danr

Administrator
Staff member
Was what I was seeing an actual break between ac3 streams or something else?
I think something else. Perhaps the rest of this reply will make sense of it.

What do you mean by "off-screen audio frames" ?
Lets say you see 10 video thumbnails on screen. And for arguments sake, that equates to 11 audio frames. What was happening was that VideoReDo would seek to the general location, but before the first video frame, and collect all the audio audio frames that encompass the displayed video. Some of these frames might occur prior to the first displayed video frame, even as much as a 1/2 second prior. While these audio frames are not displayed, they are off-screen, they were being used to determine the scaling of the graph. As you move the thumbnail, even by one frame, the number of off-screen frames, and the scaling could change radically. That's why the graph might suddenly change shape.

In beta build 472, the scaling logic only uses the audio frames that are actually going to be displayed. This should reduce, somewhat, the jerkiness of the display as you shift around.

Regarding the AC2.0 vs. AC5.1. Do you have files that use that? So far, what I've seen are AC5.1 with rear channels not being used during commercials. We do keep track of the number of encoded channels (2.0 vs 5.1), but not the difference in the actual sound levels of each the 5.1 channels.
 

litz

New member
They don't actually change from 5.1 to 2.0 ... it does exactly what you see - the sound collapses to L and R front ... but there is a definite, noticeable change (as you could see in the two .jpgs) when they switch streams from the network/show stream, to the local/commercial stream. That's what we'd be looking for, to mark ...

If the waveform is accurate (and I've yet to try 473 on the same files) it would manifest as a collapse from 5.1 to 5.1 with just L and R, and a sudden jump in volume.

The difficulty is, I don't think the acual ac3 stream itself will show any change - running the audio through besplit or azid, it shows no timestamp jumps, or packet errors.

- litz
 

litz

New member
Okay, check in 473, the waveform seems to be a lot "hotter", amplitude-wise, than it did before, but I still see the same effects.

Using the same audioclip.ts file, go to http://terminus.litz.org/videoredo/ and look at audio1-473.jpg through audio6-473.jpg

1-4 show the point where the audio "jumps" (like described above) - that hasn't changed and still can be seen.

However, note that the time is now exactly 1 frame off than the frame highlighted on the thumbnails ... this is consistent throughout the file.

5 shows a problem at the very start of the file : no audio display at all for the first few frame, and 6 shows a random spot in the middle, where the frames at the start and end of the thumbnail have no audio display either.

Also, in higher thumbnail resolutions than 1 frame (eg .25 seconds, .1 seconds, etc.) the last frame displayed has no audio display.

Hope this helps! :)

- litz
 

Danr

Administrator
Staff member
The next build 474 will fix the frames not starting and stopping exactly at the beginning of the thumbanils. The first few frames of the file may indeed have no audio, so that's probably correct.

Build 474 will also have a feature where wou can dump the audio display data, in numerical form, to the log file. Should let you look exactly at what's being graphed.

FYI, for some reason my monitors aren't bright enough to see the audio graphs on your black background. How about using a brighter line in the future :)

Also, since you're using a black background, the selection times are not visible. Do we need an option to set the selection time colors or don't you care?
 
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