No VO. Why?
January 25, 2012 2:34 PM   Subscribe

What reasons are there for a video not play the Voice over part on some Macs and some PCs?

Quick explanation:
On some PC laptops and on some Macs, you cannot hear the voice over on a video prepared for us by a videographer. We cannot fathom why? Can anyone fathom?

Longer explanation:
Company has a beautiful video about girls in Burkina Faso made by a professional video editor. We have a DVD of it. One person here complained that she couldn't hear the voice over when playing it on her PC laptop (Win 7). I was able to. But on my Macintosh (older but has lion) I could not either.


If she puts headphones on, she can hear the VO. If I attach speakers to my Mac, I can hear the VO.

I'd chalk it up to some bizarre speaker/sound card configuration that just happens to be my Mac and her PC, both of which have been around the block a few times.


At least one other person in the company had the same issue on her pc laptop, and my wife had the same problem as I do on her laptop, as does one other Mac here.

We tried various codecs (recommended by the videographer) and also playing it through VLC. Nothing. I converted just the audio part to .wav - same problem. Video maker said, and I've verified that the audio is AAC, stereo, 48khz, 192kbps.

Left and right channels look to me like they have the same waveform, and I can hear the VO from both sides through headphones. Interestingly, he has the videos on Vimeo - and all who have a problem with the DVD have the same problem listening through Vimeo. Codec wouldn't matter - it is all .f4v streaming from their server, so it has to be something (or two things mac and PC) with our built-in speakers - I am figuring - but what? What?

Here is the link for the video.
Other videos by him have no problem. He has been really good in trying to figure this out, but we are both bereft of ideas. Again, if it weren't for other people having the same problem, I'd say forget it.

Two more things,
in VLC, when I select the audio channel, if I select left or right, I can hear the VO fine.

Just for fun I played this in the HTML5 beta on Vimeo - made no difference.
posted by xetere to Computers & Internet (8 answers total)
Very odd. I'm sitting here in an edit suite and when I play the file back (through Chrome) with both channels turned up on my mixing board the VO disappears, like you said. The only thing I can think is it's some kind destructive interference between the two channels. Why you would be getting that I have no idea. I would try exporting the video with mono audio to start and see if that fixes it. Was the audio recorded in true stereo or is it a mono file that has been panned to both channels?
posted by nathancaswell at 3:15 PM on January 25, 2012

PS, I'm no audio engineer but if this is a phase, or destructive interference issue it would make sense that you wouldn't hear it in headphones, as each ear would hear each channel separately. Once you switch to speakers the two waves can now cancel each other out and you're hearing the messed up waves.
posted by nathancaswell at 3:22 PM on January 25, 2012

PPS - Further data point, if I stereo pan the two channels the VO comes back. So what we have is:

Just left channel panned center - VO
Just right channel panned center - VO
Both channels panned center - Nothing
Left channel panned left and right channel panned right - VO
posted by nathancaswell at 3:35 PM on January 25, 2012

It *seems* like one channel is using an inverted waveform, as Nathan suggests, except that I'm trying it with headphones now and can't hear the VO. Now, this could be because the soundcard on my machine is doing some pre-mixing of channels to avoid harsh stereo separation.

The easiest way to test would be to invert the waveform of one channel in any standard sound editing program and see if that makes a difference.
posted by balistic at 3:38 PM on January 25, 2012

Wow thank you guys so much, am at home so can't work on it, but will first thing tomorrow AM.

BTW I did export the video as mono and got the same results. I will ask the editor how he recorded the audio.
posted by xetere at 4:12 PM on January 25, 2012

Yeah, re-exporting it as mono from a render of the edit wouldn't fix it. If I had to guess what's going on I'd say he has a stereo sequence but a single mono track of the VO that he duplicated in his NLE and panned one version left and the other right and they are phasing each other out for some reason. This is why your music tracks are fine (they are true stereo tracks).

I do this all the time because I like to keep VO on 1-2, SFX on 3-4 etc and it annoys me visually to mix mono and stereo tracks. I also sometimes do it because Final Cut tops out on +12 db on an audio clip and I'm too lazy to apply a gain filter to get more volume.

Anyway if my theory is true that that's what he did I bet if he deleted one of the 2 mono tracks and panned the other one back center it would fix the issue.
posted by nathancaswell at 7:42 PM on January 25, 2012 [1 favorite]

Just came in to Nth the "out of phase" idea. I'm positive that is the issue. I listened with headphones on my iPhone, no problem with the dialogue. Listened with the (mono) internal speaker, nothing left of the dialogue but some strange artifacts.

The editor has either:
1. Two tracks of dialogue, or
2. A single stereo track.

If he has two mono tracks, just have him delete one of them and center pan the remaining. If it is a stereo track, he needs to split it into mono first then do as stated above.

For fun, play this through two speakers that you can physically move. Start with them right next to each other and then move them slowly apart. You will hear the dialogue move in and out of phase, meaning that the volume of the dialogue will rise and fall, while the music stays the same!
posted by stephennelson at 10:26 PM on January 25, 2012

Thank you all so much. I did as nathancaswell and stephennelson suggested and all is well.
What a frustrating problem, but glad there is now a solution. Again thanks!
posted by xetere at 7:07 AM on January 26, 2012

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