any tips for downsampling 5.1 audio to stereo?

thornburgh · Post by **thornburgh** » Tue Jun 30, 2009 1:47 am

When I do this in VS X2 Pro, the sound seems to suffer a lot. Most obviously, it gets a lot quieter. But if I crank the volume, it also seems to have noises and distortions not present in the original.

This makes me think that VS is not good at converting 5.1 audio into stereo. Is there anything I'm missing?

I'd also be happy just to preserve the 5.1 audio, but that's not available in HD resolutions as far as I can tell. Only DVDs get that option.

Thanks.

Trevor Andrew · Post by **Trevor Andrew** » Tue Jun 30, 2009 10:05 am

Hi

I would have thought HD supported DD 5.1

Ken is probably your best person to ask, in the meantime look hear.

Info on HD
http://www.videohelp.com/hd

Just a thought from VS
If you use Make Movie Manager you should be able to create your own template, using your video files properties.

Post by **Ken Berry** » Tue Jun 30, 2009 2:35 pm

As far as I am aware, at least some AVCHD cameras use 5.1 Dolby. But not HDV cameras, which use mpeg layer two.

thornburgh · Post by **thornburgh** » Tue Jun 30, 2009 7:18 pm

Thanks for the suggestions. Unfortunately, the template maker is very limited. It won't let you choose 5.1 sound unless you choose to make a DVD at DVD resolution.

Post by **Ken Berry** » Tue Jun 30, 2009 10:46 pm

You still haven't given us the properties of your original video apart from indicating it has 5.1 Dolby audio. Please right click on a clip inside Video Studio, either in the timeline or in the library window, and copy down all its properties here please.

thornburgh · Post by **thornburgh** » Wed Jul 01, 2009 5:28 am

Here are a properties of a couple files I've tried editing, but my issue really seems to extend to any 5.1 HD file.

MPEG-2 Video
24 bits, 1920x1080, 16:9
29.970 frames/sec
16000 kbps
Dolby Digital Audio
48000 Hz, 5.1 Channels
Layer None
384 kbps

H.264 Video
24 bits, 1280x720, 16:9
23.976 frames/sec
Variable bit rate (Max. 40000 kbps)
Dolby Digital Audio
48000 Hz, 5.1 Channels
Layer None
384 kbps

Neither one of these sounds that good when saved as stereo mpeg audio, and I don't seem to be able to maintain either resolution while using Dolby 5.1 audio. I also don't seem to be able to save either one without re-encoding the video.

Thanks for any help.

Post by **Ken Berry** » Wed Jul 01, 2009 6:20 am

Can I ask which cameras these two clips came from, please? I ask because there seems to be something just a little strange about each of them -- at least to me...

The first appears to be HDV/mpeg-2 except that all HDV that I am familiar with uses mpeg-layer 2 audio and a frame size of 1440 x 1080, and would have a CBR bitrate of 25 Mbps. (Was a Field Order given? Normally, HDV is Upper Field First.) I am guessing this footage may have come from a JVC dual purpose (HDV and AVCHD) camera that uses a JVC variant of HDV (.tod?) that might give those properties (though the bitrate still seems strangely low).

If this footage is indeed from a JVC hybrid camera, there is at least one user here who has such a camera. Hopefully he may see this and have some practical suggestions.

The second clip at first glance would appear to be from an older AVCHD camera -- though I cannot account for what seems to be an extremely high bitrate (VBR max 40,000 since this would put it in the range of one of the latest cameras using the new average VBR of 25 Mbps. But those cameras, as far as I am aware, use a frame size of 1920 x 1080.) Anyway, it appears your footage came from a camera filming in what appears to be 720p/24 fps movie mode and this could be at least one source of your audio problem since it is possible that if you are using a template for NTSC non-movie mode, it would have a speed the same as the first clip (i.e. 29.97 fps). Thus the original audio might become distorted in the conversion. Unfortunately, though, I have never played around with 720p/24 fps footage, so cannot really suggest what might be done with that.

But for what it's worth, you can in fact make separate templates which will copy those exact properties -- though I am also not sure what you are planning to do with the final product. The templates you make this way will probably only be playable on your computer -- though they just might be able to burned as is to a Blu-Ray disc, if you have a Blu-Ray burner and player. An AVCHD hybrid disc would need to change the properties of both to 'normal' AVCHD settings, which in the case of your second clip, would mean going from 24 fps to 29.97 fps.

But to make the special templates in X2, select Tools > Make Movie Template Manager. Then in the dialogue box which appears, click the Add button down at the bottom. In the next dialogue box, give the new template a name you will remember. Then in the top box (File Path:), click on the '...' button beside it and navigate to where the file is stored. Select it, and OK yourself out of the dialogue boxes. Do the same for the second clip. Now, next time you want to Share > Create Video File, in the drop down menu which appears, you will have two new templates down at the bottom with the names you assigned them. Choose one or the other for that type of project. This will allow you to preserve the original quality of the video (without re-encoding) and also the Dolby 5.1 audio.

Note, however, that you cannot later edit either of these new templates since templates made this way are fixed. If you attempt to edit them, they simply revert to some bland standard definition mpeg template version, and you have to start all over again.

thornburgh · Post by **thornburgh** » Fri Jul 03, 2009 6:23 am

Ken, thanks for the further advice. Both of these files are actually tv shows from the internet. I think they were probably ripped from a DVR then converted to these formats. I'm wanting to extract clips from them.

I actually had tried your suggestion of how to make a template based on an existing file. It works for some files but not these. In both cases, the 5.1 audio is changed to stereo in the resulting template. The 1080 video is also misjudged as progressive when parts of it are interlaced. And as you say, you can't edit these templates manually.