update alpine, ffmpeg, compile flags, and disable librtmp

[dromer]

Sticking to the original nginx-rtmp module since that at least has predictable functionality and behavior.

Let me know if you still want librtmp (but since you mentioned you didn't know ffmpeg already had an implementation ..)

[dromer]

Actually there is ffmpeg 4.2.2 in alpine already, so maybe we can just use the binary package instead? (will test later)
Unless there was some specific reason you wanted to compile it yourself.

[actually 4.2.2 is in edge, but 4.2.1 is in 3.11]

[alfg]

Actually there is ffmpeg 4.2.2 in alpine already, so maybe we can just use the binary package instead? (will test later)
Unless there was some specific reason you wanted to compile it yourself.

Thanks. I'd like to keep the compiled FFmpeg since it gives more control over which codecs and flags to use, especially to those that fork the project and modify it to their own.

[alfg]

Thanks!