Script to demux, add silence, resample (stretch) and remux AVI file.

[rodp]

Hi Everyone,

I produce videos from powerpoint (using moyea PPT to Video Converter) for work. We've chosen to write it in AVI, MS MPEG4 V2 as it's the most versatile for us to use online and back in powerpoint as a video. The Audio is currently MP3 but I can write the audio in PCM at time of production (if this makes the solution to my problem easier).

We always have problems with audio sync when creating the video. I have to mess about shifting the audio slightly and stretching / resampling it. I do this by using Video Pad (to get an idea of how much silence I need to add at the beginning and how much the audio needs to be stretched (it's only a small amount but the problem with video pad is you are limited to whole integers in changing the clip speed, so it's not accurate enough). I've tried using Syncview but it's a little complex and so I need something which can do this all in one in a script.

In the current video I'm working on, I have confirmed that I need to reduce the length of the audio by about 1.5% and add 0.8s of silence at the beginning.

Please could someone help me write a simple script which will split the audio and video (demux), resample the audio so that it lasts 1.5% less in time (potentially maintaining pitch but if only tempo - no one will notice that slight change), add in 0.8s of silence to the beginning and then join (remux) the video and audio back together. This should mean no loss of video image quality. One question I have though, does it matter the audio clip is not entirely the same length as the video when remuxing?

Hope someone can help / point me in the write direction in the batch script and with which command lines tools are best.

Many thanks in advance

Rodp

[Cornucopia]

Sorry, don't have a batch script. And I honestly don't think you could do that with a standard script. AFAIK, there is no scriptable app that does all you are asking (A+V demuxing, A-time stretch, A-append silence, A+V remux). Plus, why make a script if probably EVERY video you create is going to have different (even if somewhat slightly) parameters? Just manually do it.

Or better yet, use a better tool to make your video...like PowerPoint 2010 (or 2013). It has nearly foolproof Convert-to-Video capabilities (finally!), that doesn't go out of sync. And you can choose a much better codec (you can install 3rd party codecs & plugins) than the current one.
BTW, MS MPEG 4.2 went out of style about 7 or 8 years ago. Divx/Xvid was much better quality & compatibility & ubiquity, and AVC/h.264 is even better still!

Scott

[rodp]

Hi Scott,

Thanks for the prompt reply. We're still using powerpoint 2000 at work but are steadily moing to powerpoint 2007 but still, as you say, it's not really until 2010 when sync no longer becomes an issue - we could certainly look into getting a few licenses. The reason I need to pick on a older codec is that most our PCs in the business are still using XP . My PC is windows 7 but I have to cater for those using XP (and windows media player 10 upwards). Installing 3rd party codecs is not possible in the businesss without IS making me jump through flaming hoops blind folded! I've been down that route and the easiest way is to try and use what we have. I did to be honest test out DivX which worked fine on windows 7 machines but not on XP machines as WMP was too old to be able to do it natively it seems. We can use flv however, but I've come across a much wider range of programs and tools to try and sort out AVI files so have stuck with that.

By all means, if you know some command line tools which work well that can do the different steps i need, then that's a start and I can start to think about writing some sort of dos script to work through it automatically. The reason I'm trying to automate this is so that other people without a major understanding of video editing etc can do this instead of me

Any other recommendations / thoughts, please do let me know.

Thanks

Rodp

[rodp]

..

[Cornucopia]

You may want to take a look at a number of my older posts that go into possibilities for PPT->Video or PPT->DVD conversion. In your case, a 2-machine PLAY->Record, PC-> DVD-recorder play/record chain, or 1-machine (POWERFUL!) w/ screen cap might be good options.

I would STRONGLY suggest something different regarding codecs. I manage ~100 PCs at my current day job, and all but a handful are XP circa 2005-7 ~1GBRAM, and all of those would do fine playing Xvid-encoded AVI.
Or,
You could create your master and then convert to WMV9. Totally compatible with XP, no 3rd party plugins necessary. Similarly w/ MPEG1 (though not as efficient quality-wise). Never had sync issues with any of those.

You should at least be making your MASTER at lossless/visually-lossless quality on a decent NLE on a recent, reasonably powerful machine, and then exporting to your final audience-compatible codec as the last step, so you won't have to worry about sync. But not a no-name PPT->Converter and not to MSMPEG4.2!

Scott

edit: you are wasting time trying to fix a problem that should never have existed in the first place. Fix the underlying difficulty and the rest will naturally fall into place and you can get on with the task of making good PPT and good video!

[rodp]

HI Scott,

Understand what you're saying totally - if it was just me I would be using the latest codec, the latest powerpoint or have 2 pcs. But the problem is I don't I'm afraid and I'm tasked to develop a process which is simple and will run on many of our PCs at work. I will however try some different output formats of said software to see if I can find one which will always produce an in sync output (but so far no luck) and then recode to a more generic and compatable format but this of course means you start to lose quality.

However, if I was to persevere with the writing of a script (which personally i think is possible - it's just that I've not used the likes of ffmpeg, avisync, memcoder through the command line tool before) could you or someone give me some pointers. Perhaps I'm writing this thread in the wrong forum - would the video or audio forum be better? How do you move a thread?

Any further thoughts / ideas most welcome.

Thanks

Rod