Magnetic tape didn't come out until the 60's for wide spread use, so how did they get sound in the 40's and 50's when they would record things like interviews of people for the news and other broadcasts where they didn't have a studio, had to be portable and had to make it to broadcast the same day?
You are asking two quite different questions, so I will answer this bit first.
During WW2 they were having a pretty serious war, so TV, in particular, took a "back seat".
Even the TV transmissions in the late '30s in the UK & Germany were pretty limited, as were those in the USA a bit later.(both the UK & Germany shut down their transmissions on the onset of War in 1939).
Sound broadcasting of outside events was pretty much established, usually by providing "programme lines" hired from the "telephone company".
If you listen to old broadcasts, you will notice a variation in sound quality between when the Radio station had the luxury of proper "broadcast programme lines" which had to meet quality specifications, & when they needed to just grab an ordinary "phone standard" line.
If the event sound needed to be recorded, there were machines at the studio, where it was done onto conventional discs you could play on a "quite large" record player.
Film newsreels (the ones they used to have in theatres when I was a kid) were, again, mostly scheduled events, & the newsreel cameras, either had synchronised disc cutters, or optical recording, & later on, tape, either synchronised, or a magnetic stripe on the film)
You really have your timeline "out of whack" on tape recording, though, "reel to reel" tape machines were pretty much mainstream by the mid 1950s, being widely used in Radio station studios.
I had heard horror stories by "old timers" of having to lug the first portable reel to reel machines around.
(They were made to much stricter standards than the "home" ones which were available, & quality meant "heavy"in those times).
TV Studios usually, if they could, (scheduled events), set up an Outside Broadcast van, set out lots of microphones, & conventional studio cameras, send the video & audio back to the studio for recording, either by conversion into either sound film, or in the later 1950s, recorded on a studio Video Tape Recorder (VTR). Unpredictable events were either covered silent, with an accompanying commentary, or using a sound camera.
I know with projectors the sound was made from blowing air through holes on the side of the film,
No! No! No! The holes on the side of the film were to fit onto sprockets to accurately transport the film, & sync it with the shutter.
The air blowing was to suck the film into position as it passed the gate.
There is a whole lot more to film projectors than meets the eye.
but you can't record like that. If you recorded by a light onto a film track you could only measure amplitude since they didn't have lights that could pulse at 15k hz.
dmills has already covered this admirably, but I will go over it a bit, too.
The lights didn't have to "pulse", they just varied the light output at an audio rate.
It wasn't "rocket science" even then (1920s),-- people had been playing with "light beam communicators" for decades, so they really just had to split the system so instead of a transmitter & receiver, there was a recording medium in the middle.
I say, "all", but to actually do that, standardise it, manufacture equipment & supply it industry wide, was a
marvel of both engineering & organisation.
The film industry was big enough to do that, so when TV came along, there was a solid engineering base to work with.
All the home movies I have such as my grandparents wedding after WWII had no sound.
Only the very rich could afford sound home movies until magnetic "stripe" tracks became available.
Even if you could pulse light that fast how would you record more then just a single tone since the light can't make two separate pulses at once?
I also imagine that even when having a separate sound recording syncing up the sound to the picture was hard.
Covered well by
dmillsIs that why they have that black and white thing they snap down when they start a scene they start the sound when they hear the snap line up with the frame that the top part snaps down? What is that thing called? I think they use an ipad for it now a days.
There is a very large crew at a "film shoot", all of whom need to be aware that the "shoot" is underway.
The filmed image of the "clapperboard" also signals the film editor that all before that is not valuable material, & can be removed, if required.
They used clapperboards back in the days of silent movies, so, although it is useful for the sound people, it is not the original purpose.
When did they stop using actual film in the 90's?
For TV, as soon as they possibly could!
Trying to incorporate film into a studio produced programme was always horrific, with the difference in picture quality, gamma, etc, being glaringly obvious.
When I worked in a TV studio in 1965, we were still trying to do this, but by the time I worked in another such studio, in 1988, it was long gone.
I liked the way film looked, you could see this best on dr who where dr who had the afro, the indoor shots were on video tape and the motion looked sharp. Then outdoor shots were more smooth with a soft focus and bright lights not over exposed leaving trails.
To each their own---- I hated it!