This app was mentioned in 7 comments, with an average of 1.57 upvotes
I use Pulseaudio networking features, they are great actually. I plug in the headphones into my phone, run Simple Protocol Player and watch movies on a sofa, listening to the audio in headphones without long extension cord.
I also use expander filter for the microphone, it drastically reduces background noise. Although Pulseaudio does not directly support filters for inputs, it works rather fine with some hacks (like making fake output, looping back microphone input to that output and adding LADSPA filters for the output).
I've done it before using PulseAudio with Simple Protocol Player - I'm not sure if libreelec's pulseuadio already has simple protocol plugin, if it does the only server-side stuff is starting the protocol server as described on the github page linked on that google store page.
Worst-case you can just auto-run the server manually if changing the pulseaudio config is difficult:
pactl load-module module-simple-protocol-tcp channels=2 source=replace port=12345 record=true
You'll need to replace the source= section with the appropriate one based on pactl list sources short
The latency isn't bad - usually only a few ms that's mostly unnoticable, but as with any network audio jitter can be annoying and causes occasional pops/clicks/audio drops. IIRC I also had issues with the phone going in to low-power when the screen goes off the latency would go crazy.
module-simple-protocol-tcp yay!
I'm still waiting for a native pipewire way to stream my sound to my android device that works better.
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^pactl ^load-module ^module-simple-protocol-tcp ^source=65575 ^record=true ^port=3000 ^format=s16le ^rate=48000 ^channels=2
^https://play.google.com/store/apps/details?id=com.kaytat.simpleprotocolplayer
I use a linux based Kodi, so I set pulseaudio to send out 'simple protocol' audio and connect to it with this app
The documentation of the app tells you how to set up the server host.
There's no noticable audio delay with the default 50ms buffer, you can set it even lower if you want. The only problems I've noticed is some phones go in to a 'low power' mode and it seems to start 'clipping' - though doesn't seem to actually be overrunning the buffer.
Phones use Bluetooth to send audio, not receive audio, you will need some serious hackery with drivers to make your phone behave like a headset.
The best you can do is to send files over Bluetooth, ten megabytes per minute. WiFi is much more versatile.
If you want to stream audio from your laptop to your phone, and your laptop runs Linux, you can install PulseAudio output plugin to your phone, and configure your PC to stream audio using TCP connection.
The same developer provides a hackish PulseAudio server for Windows, which can be used to stream audio to Android plugin in the same way.
There are also AmpMe and SoundSeeder apps, that can 'stream and spread your music at home or on your party to multiple devices', as their description says.
Or you can install one of DLNA server or client apps, I did not manage to understand who will actually play the audio - the server or the client.