Enable pausing and resuming of stream

[yannikwirbs]

Video and audio output pipe are on hold while paused.
There is no video or audio in discord.
Maybe there is a way to implement a way to send a still image to the video.
Video and audio are not desyncing.

REFERENCE ISSUE: #5

[longnguyen2004]

I'm wondering how this will behave in an actual live stream, and whether stream backpressure will be a problem.
Also, eloquent-ffmpeg has a built-in pause and resume function, maybe we should look at that as well?

Repeating the last frame is definitely not possible, since it'll break the bitstream.

[longnguyen2004]

Investigating RFC 7728 is also interesting Ignore, this is for a receiver to request a pause

[s074]

This will also only work if noSleep is disabled.

From looking at eloquent-ffmpeg it seems it just suspends the process and then resumes it, like some people were already doing using SIGSTOP and SIGCONT

[longnguyen2004]

like some people were already doing using SIGSTOP and SIGCONT

And it also works on Windows using the undocumented NtSuspendProcess and NtResumeProcess functions, so that's a plus.

I also wonder how the functionality should be exposed to user code. Maybe we'd need to create some kind of playback controller object, with play(), pause() and stop() functions.

[BitcircuitEU]

@longnguyen2004 while implementing ffmpeg api in nodejs maybe make a pause function that stores current timecode of demuxing and continue from there if possible. Not sure if SIGSTOP and SIGCONT is that reliable.

[Giggitybyte]

Anybody taken a look at this recently? Would be nice if this was built-in to the library.

[longnguyen2004]

I've thought about it a few times, and I think that video playback management should be best left to a proper video playout system, such as ffplayout or CasparCG. Bare ffmpeg doesn't give much in terms of control, and the method in this PR can cause problems when pausing for a long time

[yannikwirbs]

What problems are there? I am by no means familiar with ffmpeg, but it seemed like a good idea suspending the callback. The only things coming to my mind that might be causing problems for long periods is the pipe breaking or ffmpeg to stop after long idle, right? But I get that you would rather have proper handling. It's been some time, do you want to close the PR?

[longnguyen2004]

I'll close it when I can come up with something better. Maybe it'll be something over at https://github.com/Discord-RE/FFmpeg-input-premade that integrates CasparCG for a complete solution