Converting audio on an AVI file?

[toji53]

I’ve been authoring some DVDs using some software and I can only fit about 70 minutes of AVI video on a DVD. I’ve tried to do some research and I think what’s causing this is the audio. I’ve read that I could save a lot of space if I converted the LPCM audio to AC3. What I haven’t figured out is how to do that.

I’m really new to manipulating video/audio files, but can anyone point my in the right direction?

Thanks!

Edit: I've read that "DVDit PE" has the ability to convert the audio, but does the software "DVDit Pro 6" have this ability?

[Wile_E]

I suppose you meant 70 minutes of MPEG2 on a DVD. Because for DVD, MPEG2 is the video format used. Anyway, there are a number of tools you can use to convert PCM to AC3. Besweet is one free tool. You can also buy TMPGENC AC3 plugin for $29, that can also be used as a standalone program. It is Dolby Certified.
http://www.pegasys-inc.com/en/product/tsp_ac3.html

Look under the tools section of this videohelp for more.
https://www.videohelp.com/tools

[redwudz]

What I do is save out the audio in WAV format using VirtualDub Mod or similar. Then convert the audio to AC3 with ffmpegGUI. They are both freeware programs. BeSweet is good, but a little intimidating to newcomers.

[toji53]

redwudz,

Ok, after I've created the WAV file and converted it to AC3, where do I go from there? How do I replace it with the original audio file?

Thanks for the help BTW!

[celtic_druid]

ffMPEG can convert the audio directly from the avi. No need to demux or decode to wav first.

Take m2v (video) file, take AC3 file (audio), drop in authoring app, author and burn.

[toji53]

Ok, I believe I've figured out how to replace the orginal audio with the AV3 file, however, it doesn't appear to take up less space than the original file. The video itself (about 22 minutes long) still takes about 1/3 of the DVD. Both audio files take up about .3 GB.

Any thoughts?

[celtic_druid]

0.3GB = 307MB's. 1/3 of a DVD is more like 1,492MB's.
Maybe whatever software you are using is re-encoding it?

[toji53]

The audio only takes up .3 GBs, and the video file takes up 1.47 GB.

I'm trying to figure out a way I can fit more than 60-70 minutes of video onto one DVD. Should 22 minutes of video alone take up that much space?

[celtic_druid]

Use a lower bitrate. That's what 7-8Mb? The lower the bitrate, the smaller the video will be and therefor the more you can fit. Also the lower the bitrate, the lower the quality.

[toji53]

I see! Thanks!

The previewer doesn't appear to change when I change the bitrate. Would the difference only be visable once it's burned and being watched on a television?

[celtic_druid]

Depensd how the previewer works. Definatly no need to burn though. Just play after encoding.

[toji53]

So what do you think about the audio? It appears the AC3 file is actually a good deal smaller, 31.1 MB while the original audio file is 283.5 MB (does that make any sense?). However, they appear to take up the same about of space when added to the DVD. Any idea why?

[celtic_druid]

As I said looks like maybe the software you are using is re-encoding.

My advice would be to use different software.

[Abond]

I think you are adding the ac3 file to the program mpeg stream which has already LPCM, therefore the file size is nearly the same. To replace the audio you need to demultiplex the mpeg to m2v and wav and then add to the authoring program m2v and ac3 files. Look at the guides for demultiplexing - there should be enough information.
I would suggest ReJig or DGIndex for demuxing.

[toji53]

I see. And if the files are currently in AVI form I need to find a way to convert them to MPEG before demuxing?

[Abond]

Then you demultiplex the video and audio from the avi (VirtualDub). The video you convert to mpeg and the audio to ac3 separately. Then you give them (m2v and ac3) to the authoring program that will combine (multiplex) to DVD vob files creating all other necessary .ifo and .bup files, in fact creating the DVD.