Audio Problem with Video2NBTV?

[ac7zl]

I wonder if anyone has experienced this problem:

Using my computer and Windows Media Player, I preview a video clip--- picture good, sound good.

Using Video2NBTV, I convert that clip to NBTV format.

Using "The Big Picture," I view the converted file. The video is nice and clear, but the audio is heavily distorted...it sounds as if it is overdriven.

If I use the same viewer to view NBTV club material, both the sound and picture is good.

It seems as though the video-to-NBTV audio conversion is "hot." Has anyone experienced this? Is there a workaround/fix?

Regards,
Pete
AC7ZL

[DrZarkov]

Yes, I had that problem before. Easiest workaround: Use the software "Super", http://www.erightsoft.net/SUPER.html, to convert the video to another format. I use mostly "MPEG as in VCD", but it should be enough to change the audio codec.

[Viewmaster]

I've had trouble that too as though the sound is over recorded and gets clipped.

Under 'source' if I use Colour audio file instead of audio file there is less or no distortion on a converted NBTV file. Whether this will work on all such files I know not.
Albert.

[DrZarkov]

What's worse: it does not work when I display it on a real monitor. So it's better to convert it to another format before converting it to NBTV.

[gary]

I wonder if anyone has experienced this problem:

Using my computer and Windows Media Player, I preview a video clip--- picture good, sound good.

Using Video2NBTV, I convert that clip to NBTV format.

Using "The Big Picture," I view the converted file. The video is nice and clear, but the audio is heavily distorted...it sounds as if it is overdriven.

If I use the same viewer to view NBTV club material, both the sound and picture is good.

It seems as though the video-to-NBTV audio conversion is "hot." Has anyone experienced this? Is there a workaround/fix?

Regards,
Pete
AC7ZL

Yes, there was mention of this in another thread. The reason is because when the audio is of another format to that of NBTV (44.1kHz, 16bit, PCM) it needs to be converted. If there are no other codecs installed on the system DirectShow defaults to using the ACM (Audio Compression Manager). This converts just about everything - but not very well, and one of the problems it has is that in some conversions it adds a significant amount of gain so that if the audio already had a high dynamic range it gets clipped. This in itself is not a problem but unfortunately it doesn't truncate the over amplified sample it just bit extends it such that the result is undefined, hence distortion.

Since this is happening in the filter graph there is nothing that my application can do about it (although I am investigating placing a level control into the graph before the acm filter).

Currently the only workaround is to reduce the gain of the audio prior to passing it to Video2NBTV somehow.

[gary]

What's worse: it does not work when I display it on a real monitor. So it's better to convert it to another format before converting it to NBTV.

That I don't accept, the audio problem has nothing to do with the video at all. In any circumstance, the video should play perfectly and the audio should also play but, in some cases, sound distorted.

If you believe that this is incorrect can you send me a sample video that exhibits this problem please.

[DrZarkov]

No, Gary, that's what I've ment. When the sound is disorted on "The Big View" then the problem is the same with the monitor. The picture is course good!

[gary]

No, Gary, that's what I've ment. When the sound is disorted on "The Big View" then the problem is the same with the monitor. The picture is course good!

Ah I see what you meant now, yes the problem is generated by the conversion process and has nothing to do with The Big Picture, it just plays what's there just like your monitor.

[gary]

Ok, there is a new version of Video2NBTV here:
http://users.tpg.com.au/gmillard//Video ... elease.exe

which adds a "reduce audio by 3dB" facility. This inserts a DirectShow in-place transform filter into the filter graph *before* the ACM wrapper filter so that when the ACM increases the gain it should not clip.

Two things:

Be aware that the installation package will now install and register a DirectShow transform filter called "NBTV2Video -3dB audio gain transform" onto your system.

This may not work with all video sources, namely those (if they exist) which do not present PCM to the ACM filter.

I would be interested in getting feedback from those that try this in case the 3dB attenuation is not enough.

Cheers.

[ac7zl]

Thanks for modifying your code. I tried it this evening.

It seems to be a step in the right direction, but it's not enough. Quiet passages seem to be ok, now, but most of the audio is still distorted.

Pete
AC7ZL

Ok, there is a new version of Video2NBTV here:
http://users.tpg.com.au/gmillard//Video ... elease.exe

which adds a "reduce audio by 3dB" facility. This inserts a DirectShow in-place transform filter into the filter graph *before* the ACM wrapper filter so that when the ACM increases the gain it should not clip.

Two things:

Be aware that the installation package will now install and register a DirectShow transform filter called "NBTV2Video -3dB audio gain transform" onto your system.

This may not work with all video sources, namely those (if they exist) which do not present PCM to the ACM filter.

I would be interested in getting feedback from those that try this in case the 3dB attenuation is not enough.

Cheers.

[gary]

Ok Pete, I didn't have a video sample that exhibited this problem to a great extent (I have however come across one in the past) so I have just assumed that the acm could not possibly be increasing the gain by more than -3dB. I will make this a user settable value soon, but in the meantime can you send me a short sample of the video you are having this problem with so I can test it please?

Cheers,
Gary

[ac7zl]

Gary-

I've just tested your -3db option with a number of other clips, and it seems to work fine. Converted clips that distort when translated at 0db come at fine with the -3db box checked.

The clip that originally brought this to my attention is actually a very old cartoon feature, many minutes (and many megabytes) long. I need to get the tools to cut it down in order to make it post-able or email-able size.

In retrospect, it seems that there is a certain amount of distortion inherent in the clip (late 1920's or early 30's vintage) so it is difficult to tell if the 3db cut is sufficient or not.

The user-adjustable setting sounds like a great idea.

Pete
AC7ZL

Ok Pete, I didn't have a video sample that exhibited this problem to a great extent (I have however come across one in the past) so I have just assumed that the acm could not possibly be increasing the gain by more than -3dB. I will make this a user settable value soon, but in the meantime can you send me a short sample of the video you are having this problem with so I can test it please?

Cheers,
Gary

[daniel gosson]

I have had no problems with distortion in the actual video when played on my disk televisor, however they do distort the sound when played in the big picture.
If the original video sound was a sample rate other than 44.1 ( such as 48kbs dv avi as in my case) there is some alias distortion present, however it is extremely mild. I get around this by processing the soundtrack outside of NBTV software completely & adding it later.
Converting to NBTV from some formats like WMV or MPEG that use temporal compression suffer shocking lip sync promlems. I have had no problems with this using AVI vids that only compress spatialy like DV AVI straght from the camera.