How many ffmpeg instances are you holding in memory? You have a single ffmpeg process for each upload that is happening, do you? Additionally, if I am uploading files with B-frames and GOPs of 300 (which I assume will lead to a lot of frames being kept in memory, not sure about this), is your RAM requirement not going to be massive if you have several uploads happening at the same time? And considering the length of time a single video takes, it's reasonably likely you'll have a lot running in parallel, is it not?
We have one ffmpeg process for each upload, yes. From our tests with the kind of videos we mostly deal with (user generated content), this seem to work quite well while only requiring reasonable memory allocations.
So sure, there could be problems we don't know about yet, but that's the price for doing something nobody has done before. We will deal with these problems as they come up. In the worst case that might mean falling back to normal encoding if a ffmpeg child process starts to misbehave.
We are feeding raw bytes into a command line ffmpeg process via standard input.
Ffmpeg only reads as much from stdin as it can process. Node.js gives us a 'drain' event when this happend, which means we can pump more data into it. So we are no throttling the speed, just the flow of data.
