webcam to gpu encoding

record-cam.service

[Unit]
Description=Local surveillance using the webcam
Requisite=pulseaudio.service 

[Service]
WorkingDirectory=%h/Aufnahmen
# Might want to skip restarting if all you need are the first 2h.
Restart=on-success
TimeoutStopSec=10s
ExecStart=%h/record-cam.sh vaapi

SuccessExitStatus=255
Nice=-2

; PrivateNetwork=true

record-cam.sh

#!/bin/bash
# Takes the raw data stream from your webcam,
# denoises it using the CPU,
# to finally have the stream encoded by your GPU (APU in my case).
#   Zen1+ is limited to 8bpp, which is "nv12"
#   Zen2 and later is able to encode 10bpp, which is "p010"
#
# Without the trailing "scale_vaapi" you'd get a duplicate bw image.

# For a list of video formats supported by your webcam see:
#   ffmpeg -f video4linux2 -list_formats all -i /dev/video0

exec \
ffmpeg -y -hide_banner -nostdin -nostats \
  -vaapi_device /dev/dri/renderD128 \
  -f v4l2 -framerate 30 -video_size 960x540 -input_format yuyv422 -i /dev/video0 \
  -itsoffset 0.35 \
  -f pulse -i default -ac 1 \
  -vf 'hqdn3d,format=nv12,hwupload,scale_vaapi' -c:v hevc_vaapi -tag:v hvc1 -b:v 1400K \
  -c:a libopus -b:a 128K -metadata:s:a:0 language=deu \
  -map 0:v -map 1:a \
  -t $(( 7200 - 10 )) \
  "$(date --iso=minutes | cut -d + -f 1 | tr -d ':')-hwaccel.mkv"

record-cam.timer

[Unit]
Description=Record what is going on during Ruhezeiten

[Timer]
OnCalendar=Mon..Sat 5,13,20:01:00
AccuracySec=1m

[Install]
WantedBy=timers.target

stop-record-cam.service

[Unit]
Description=Stop recording
Conflicts=record-cam.service

[Service]
Type=oneshot
ExecStart=/usr/bin/true

-itsoffset 0.35 and accompanying -map 0:v -map 1:a offset the latency video encode introduces. In other words, audio shall be mixed with a delay to be in-sync with the video.

Once the file has been closed (after 2h or when stop-record-cam.service has been started) another process

• … generates subtitles and attaches them to the video file. Those subtitles display date and time.
• … creates a FFMETADATAFILE with tracks. Tracks start whenever there is a jump in loudness, e. g. from my neighbours operating machines or jumping (!!) around at night.