Are rendering times affected by audio filters??

brodwidr · Post by **brodwidr** » Tue Mar 06, 2007 8:30 am

Hi, -

I am working on a project that I had some technical difficulties with the microphone set up, and levels vary widely. So the first thing I did after bringing in the 50-min long video from the camcorder was to split the audio off and apply the amplify and volume leveling audio filters. Having done that, and verified the quality I was getting, I then made some very simple edits (cuts only) and added some titles.

But when I attempt to preview the title section after changing the titles (but nothing else about the video) I find it takes several minutes between clicking the "play" button and when the video actually starts to play in the video window. The change I made isn't affecting more than about 16 seconds of the 50 minute long video, so I can't understand why it's not nearly instantaneous to preview.

I didn't have this problem when I was just working the video and audio as part of the same clip, so I'm guessing it might have something to do with having split the audio, or having applied audio filters.

In preferences, "playback method" is set to "instant playback".

Any suggestions?
Thanks in advance.
- David

Trevor Andrew · Post by **Trevor Andrew** » Tue Mar 06, 2007 11:24 am

Hi David

I have not use the audio filters, but ran a quick test and they significantly increased the reaction time when hitting play.
You could render the video after applying the filters, but this also took ages.

Do you need the filters applied to the full 50 minutes or is it just a small section.
If so ¡¥Cut¡¦ the audio clip using the scissors, apply the filter to a smaller section.

Have you tried using the ¡¥Rubber Banding¡¦ from Audio view.
No need to split audio.
Play the project, then drag the slider to adjust volume levels.
Volume level points will be inserted, these can be adjusted to fine tune.

Regards

Trevor

Black Lab · Post by **Black Lab** » Tue Mar 06, 2007 2:15 pm

Another alternative would be:
1. Split the audio, then remove the video clips from your project.
2. Add the necessary audio filters, then render the "fixed" audio to a new audio file.
3. Start a new project, insert your video clips and mute the audio.
4. Now import your new audio.
As long as you didn't alter the length of the audio all should be fine, and because the audio filters are already rendered into the new file you won't endure any processing time during playback.

brodwidr · Post by **brodwidr** » Tue Mar 06, 2007 4:14 pm

It looks like your experience is the same as mine. It seems as though "smart rendering" doesn't apply to audio filters, for some reason. If it did, VS would not have to re-render the whole audio track each time some minor change is made. A strange software design decision....

Black Lab · Post by **Black Lab** » Tue Mar 06, 2007 4:37 pm

It's not re-rendering the audio track, it's just trying to play it in Instant Playback mode with a bunch of filters applied. Of course it is going to slow down the process. If you apply a bunch of video filters to a video clip it will do the same thing. By rendering the filtered audio to a seperate audio file you've, in essence, removed those filters (by combining them into one file), so it plays smoothly.

brodwidr · Post by **brodwidr** » Tue Mar 06, 2007 5:14 pm

Thanks for your explanation, Jeff. It makes sense.

The strange thing is, even if I move the trim handles in so that I am only previewing a very small fraction (a minute or less) of the project, it seems to take a long time to start playing (after I click "play") -- just as it does when I am trying to preview the whole project. This suggests to me that VS is applying the audio filters to the entire project rather than just the particular portion that I wish to preview.

I can understand that VS needs to collect data from the whole project in order to calculate and apply the "volume leveling" filter, but I would have expected that VS would save that data (in a temp file of some sort) from the previous time it was played, and not have to re-analyze the entire audio track each time. After all, if you use the "rubber band" capability to change the volume of different parts of the track, it doesn't slow VS down -- and what is "amplify" and "volume leveling" but an automatic application of the rubber-banding capability?

I like your idea about rendering the whole audio track with filters to a new audio file and then importing that into the project. That should solve the problem. Thanks for your help.

- David

Black Lab · Post by **Black Lab** » Tue Mar 06, 2007 5:30 pm

I can understand that VS needs to collect data from the whole project in order to calculate and apply the "volume leveling" filter, but I would have expected that VS would save that data (in a temp file of some sort) from the previous time it was played, and not have to re-analyze the entire audio track each time.

From the VS10 User's Manual:
• Instant Playback allows you to quickly preview changes in your project
without the need to create a temporary preview file, however, playback may be jerky depending on your computer resources.
• High Quality Playback renders your project as a temporary preview file
then plays this preview file. Playback is smoother in High Quality Playback
mode, but rendering your project for the first time in this mode may take a long time to complete depending on the size of your project and computer resources.

I think your best bet is to render a new audio file.

Trevor Andrew · Post by **Trevor Andrew** » Tue Mar 06, 2007 5:49 pm

Hi

I tried rendering a video earlier today using the filters.
Split Audio and a created Wav.

Render times were excessive.
I mean very long indeed.

Let us know how long it takes.

The rubber band option may-be the best solution

Trevor

Black Lab · Post by **Black Lab** » Tue Mar 06, 2007 6:04 pm

Yet another option might be splitting your audio and render to an audio file, then import that audio file into a third party audio editor such as Audacity. Add your filters there, then import back into VS. Not only does Audacity have many more filters, it probably won't choke when rendering the new file, and it's FREE.

brodwidr · Post by **brodwidr** » Tue Mar 06, 2007 6:12 pm

Hi, Trevor -

Last night I set up the render and let it run overnight. This was for a 50 minute long project where I had two audio filters, amplify and volume leveling, spanning the entire project. The rest of the project was trivial from a render standpoint.

It was done by morning (6 hours later) but at the rate it was going I estimate it took at least one hour and not more than three hours.

In the future, if I ever have a video with sound that I have to fix this way, I will split off the audio and render it separately as jeff has suggested. That seems like the best approach. In this case it's too much trouble to rubber-band all the changes manually. I was videotaping a lecture, and the speaker was properly mic'd but whenever someone asked a question, levels dropped to nearly inaudible. So levels are jumping up and down all the time. Clearly, I needed to have a wireless mic to pass around the audience, or have the audience members walk up to a stand-mounted mic. Live and learn.

Hope that helps.

- David

NoM.O · Post by **NoM.O** » Tue Mar 06, 2007 6:25 pm

In case anyone's interested, Portableapps.com have released Audacity Portable, so casual or mobile users have a lightweight, fully featured audio editor that doesn't need installation. Just extract the files to whatever directory you want and run.

Might be handy for some people.

peace.

Black Lab · Post by **Black Lab** » Tue Mar 06, 2007 6:32 pm

This was for a 50 minute long project where I had two audio filters, amplify and volume leveling, spanning the entire project...I estimate it took at least one hour and not more than three hours.

I don't think that render time is out of line.

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Are rendering times affected by audio filters??

Are rendering times affected by audio filters??

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