Why does Premiere Pro "Sequence from clip" on MP4 and then "Match Sequence" result in a massive AVI file?
You would imagine that just "trimming" an MP4 file with same setting would be quick and painless, but when I tried it the resultant file was massive - like 10x the size of the original file.
Turns out this is because the .mp4 compression means there aren't really full frames in the file just deltas.
So when you select "Match Sequence Settings", it has to give you AVI format anyway.
So this is what you HAVE to do. Go ahead and create your HUGE AVI file. Then use an app or an online service to compress it back down...
I had a good result using https://cloudconvert.com/avi-to-mp4
It shrunk the 76Mb AVI to less than half a Mb.