Video and audio lag when using v4l2 with audio file

[s0301132]

Important Information

Provide following Information:

• mpv version

  
  mpv 0.34.0-100-g0e76372e86 Copyright © 2000-2021 mpv/MPlayer/mplayer2 projects
  built on Mon Dec 13 01:57:44 HKT 2021
  FFmpeg library versions:
  libavutil       57.11.100
  libavcodec      59.14.100
  libavformat     59.10.100
  libswscale      6.1.101
  libavfilter     8.20.100
  libswresample   4.0.100
  FFmpeg version: N-104861-g7fe5c7f02d

- Linux Distribution and Version

Ubuntu 18.04.6 LTS aarch64 NVIDIA Jetson Xavier NX Develo 4.9.253-tegra

### Reproduction steps and actual behavior
According to this page [v4l Input](https://github.com/mpv-player/mpv/wiki/Video4Linux2-Input) I want to stream video from video capture card `dev/video0`, if only using `v4l2` it can play smoothly.
`mpv av://v4l2:/dev/video0 --profile=low-latency`

But after adding audio file both video and audio are laggy with lots of drop frame.

mpv av://v4l2:/dev/video0 --audio-file=av://pulse:alsa_input.usb-AVerMedia_Live_Gamer_Ultra-Video_5310975600762-02.analog-stereo --demuxer-lavf-o=timestamps=abs

Terminal output.

Audio device underrun detected. AV: 455390:42:46 / 455390:42:46 (100%) A-V: 0.000 ct: 0.673 Dropped: 41 Audio device underrun detected. AV: 455390:42:47 / 455390:42:48 (100%) A-V: 0.000 ct: 0.673 Dropped: 41 Audio device underrun detected. AV: 455390:42:49 / 455390:42:50 (100%) A-V: 0.000 ct: 0.673 Dropped: 41 Audio device underrun detected. AV: 455390:42:51 / 455390:42:52 (100%) A-V: 0.000 ct: 0.673 Dropped: 41 Audio device underrun detected. AV: 455390:42:53 / 455390:42:54 (100%) A-V: 0.000 ct: 0.673 Dropped: 41 Audio device underrun detected.

### Expected behavior
Both video and audio play smoothly

[s0301132]

I follow #8367 and config my PulseAudio now both video and audio can play smoothly. However it only works on system wise setting /etc/pulse but not user config /.config/pulse

[Dudemanguy]

Original reporter said he solved it (might be still an mpv bug somewhere but we'll close this for now).