fwiw, mpv is working for me with the present version of pipewire (1:0.3.59-7) ... after going through the process of getting pipewire going.. before that, with just alsa, mpv was refusing to work...

If you build mpv with neither of the two present it works fine with alsa. If it doesn't it is because alsa is not yet configured not because it needs something else

PKGBUILD

# by obarun-community-packagers 
pkgname=mpv
epoch=1
_tag='33f10b1aee5fef45960728fe8595d1603c8a9a85' # git rev-parse v${pkgver}
pkgver=0.35.0
pkgrel=3
pkgdesc='a free, open source, and cross-platform media player'
arch=('x86_64')
# We link against libraries that are licensed GPLv3 explicitly, so our
# package is GPLv3 only as well. (Is this still correct?)
url='https://mpv.io/'
depends=('alsa-lib' 'libasound.so' 'desktop-file-utils' 'ffmpeg' 'libavcodec.so' 'libavdevice.so'
         'libavfilter.so' 'libavformat.so' 'libavutil.so' 'libswresample.so' 'libswscale.so'
         'glibc' 'hicolor-icon-theme' 'jack' 'libjack.so' 'lcms2' 'liblcms2.so' 'libarchive'
         'libarchive.so' 'libass' 'libass.so' 'libbluray' 'libbluray.so' 'libcdio'
         'libcdio-paranoia' 'libdrm' 'libdvdnav' 'libdvdread' 'libegl' 'libgl' 'libglvnd'
         'libjpeg' 'libjpeg.so' 'libplacebo' 'libplacebo.so' 'libpulse' 'libpulse.so'
         'libva' 'libva.so' 'libva-drm.so' 'libva-wayland.so' 'libva-x11.so' 'libvdpau' 'libx11'
         'libxext' 'libxinerama' 'libxkbcommon' 'libxkbcommon.so' 'libxpresent' 'libxrandr' 'libxss'
         'libxv' 'luajit' 'mesa' 'mujs' 'rubberband' 'librubberband.so' 'shaderc'
         'libshaderc_shared.so' 'uchardet' 'vulkan-icd-loader' 'wayland' 'xdg-utils'
         'zlib')
makedepends=('git' 'python-docutils' 'ladspa' 'wayland-protocols'
             'ffnvcodec-headers' 'vulkan-headers' 'waf')
optdepends=('yt-dlp: for video-sharing websites playback'
            'youtube-dl: for video-sharing websites playback')
provides=('libmpv.so')
# options=('debug' '!emptydirs')  # #  uncomment this line to have the debug pkg produced
options=('!emptydirs')
source=("git+https://github.com/mpv-player/mpv.git# tag=${_tag}?signed")

build() {
  cd ${pkgname}

  waf configure --prefix=/usr \
    --confdir=/etc/mpv \
    --enable-cdda \
    --enable-dvb \
    --enable-dvdnav \
    --enable-libarchive \
    --enable-libmpv-shared \
    --disable-build-date \
    --disable-pipewire \
    --disable-caca

  waf build
}

package() {
  cd ${pkgname}

  waf install --destdir="$pkgdir"

  install -m0644 DOCS/{encoding.rst,tech-overview.txt} \
    "$pkgdir"/usr/share/doc/mpv

  install -m0644 TOOLS/lua/* \
    -D -t "$pkgdir"/usr/share/mpv/scripts
}

# ---- license gpg-key sha256sums ----

license=('GPL3')

validpgpkeys=('145077D82501AA20152CACCE8D769208D5E31419') # sfan5 <sfan5@ live.de>

sha256sums=(SKIP)

Skatanafas wroteIf you build mpv with neither of the two present it works fine with alsa.

yeah, i figured that might be the case, since there's nothing explicit (configurewise) in the arch PKGBUILD (beyond the hard dependency) and considered going that way..
anyway i've gots pipewire now, and it seems to be doing what it's supposed to, so far.. (and a user tree and dbus user session and xdg-user-dir services :p )

Hyperspace wrotempv has the following errors whenever I try to play videos:

[ao/pipewire] Could not connect to context '(null)': Host is down
'!impl->polling' failed at ../pipewire/spa/plugins/support/loop.c:872 impl_clear()

This results in nothing being played.

According to this thread (https://github.com/mpv-player/mpv/issues/10859), one simply needs to update pipewire to 1:0.3.60-1.

Currently, the Obarun version is at 1:0.3.59-7.

Perhaps the issue can be rectified by updating Obarun's pipewire version?

Note: I did not explicitly install Pipewire into my system, as I am still using PulseAudio.

Similar to Skatanafas' suggestion, if you're comfortable installing packages from the AUR, the mpv-git package is much more minimalistic (no pipewire dependency), uses the meson build system mpv is moving to, and seems to be well-maintaned. You can make it even more minimalistic by simply commenting out what you don't want in the _opt_features section (i.e. if you don't use wayland) of the PKGBUILD before building it.

Even though I use pipewire already, I switched to the AUR mpv a few days ago for other reasons and have not noticed any difference.

please update, it should be ok.