UKC

I've retrieved a large number of archive video clips which I took 'back in the  day' which include lots of .avi files. I'd like to convert these to .mp4 format as efficiently as possible, preferably on a laptop/desktop rather than a portable device. There are a number of programmes/apps that offer this function but I was wondering if anyone here has hands-on experience of using any of them? Batch processing would obviously be a big plus if available.

Handbrake should fit your needs 

https://handbrake.fr/

It's been a while since I've done this, so there may be better things available now, but I would use Handbrake if you want a GUI or ffmpeg for command line, which will be batch scriptable.

I can highly recommend ffmpeg if you're happy with a bit of command line action. I've used it for a few bits and pieces like this and despite knowing ~nothing about audio/video formats it seems to just work.

ffmpeg is used all across the industry so I'd hope it works! Although because it is used everywhere there can be a baffling array of options.

It's super powerful, if it's just converting file types it'll be an easy job. I can't remember the exact syntax but if you've got a lot to convert you can make a text file listing all the jobs and it'll run through the list. Perfect for doing lots with little effort.

Another vote for handbreaak. I was never intelligent enough to use ffmpeg

Perfect, thanks everyone. I'll check out Handbrake first and see how that goes.