Allow HLS preview

[lkiesow]

Instead of just allowing to show preview images, we could also allow for providing a “real” live stream since tools like FFmpeg support generating streams and we include a web server to deliver them anyway.

Generating a stream could look like this:

ffmpeg -re \
        {{ INPUTOPTS }} \
        -c:a aac -ac 1 \
        -c:v libx264 -crf 18 -profile:v baseline -maxrate 400k -bufsize 1835k -pix_fmt yuv420p \
        -flags -global_header -hls_time 10 -hls_list_size 6 -hls_wrap 10 -start_number 1 \
        preview/preview.m3u8

We could even reduce system load by using this for the recording, ingesting a concatenated transport stream at the end. But that needs some more investigation.