Having made many of the BAA’s meeting videos in the past, I would re-iterate what James and Andy have already said. It can be pretty time consuming.
In theory, it’s simple enough to wire the speaker up with a microphone, and insert an HDMI recorder between the laptop and the projector.
But that’s just the beginning.
When you get home, you’ve got a hundred GB of raw video. That needs sending (by post?) to somebody with access to (inevitably, very expensive) video editing software. First, the audio needs synchronising with the video. Inevitably, if the footage was shot by a novice, there will be problems with it (e.g. the speaker was breathing into the microphone, the microphone wasn’t turned on, etc, etc) which need to be identified and worked around. Eventually, once you’ve spent a couple of days fixing everything, you do an export to compressed web-ready video. That takes many hours of CPU time in itself.
Then, you circulate the video, and discover somebody showed copyright material on one of their slides, and you get asked to cut something out. So you have to re-export the video – which is another overnight job.
I’m as supportive as anybody of the BAA filming talks, but it’s a lot of work to expect anybody to do on a voluntary basis. And for the same reason, companies that do this professionally are also not cheap.