Documentation of --gstout-audiodevice is incorrect

[tom-ch1]

I have a Raspberry Pi 3B with HDMI and headphone jack and I want to make gmediarender use the headphone jack instead of the HDMI output. The docs on how to do that are both imprecise and incorrect:

--gstout-audiosink and --gstout-audiodevice
...You can see the available devices with aplay -L

This is incorrect in my case. aplay -L outputs all kinds of information, among others:

default
    Playback/recording through the PulseAudio sound server
hw:CARD=b1,DEV=0
    bcm2835 HDMI 1, bcm2835 HDMI 1
    Direct hardware device without any conversions
sysdefault:CARD=b1
    bcm2835 HDMI 1, bcm2835 HDMI 1
    Default Audio Device
hw:CARD=Headphones,DEV=0
    bcm2835 Headphones, bcm2835 Headphones
    Direct hardware device without any conversions
sysdefault:CARD=Headphones
    bcm2835 Headphones, bcm2835 Headphones
    Default Audio Device

setting --gstout-audiodevice to sysdefault, sysdefault:CARD=Headphones, or default all fail to output anything on the audio jack.

What does work is setting it to hw:1,0, which is never mentioned in aplay -L

Here's a hint on how I tested this on the command line to isolate the issue from other gmediarender bugs:

• does not work: mpg321 -o alsa -a sysdefault 01_New_Born.mp3
• does not work: mpg321 -o alsa -a "sysdefault:CARD=Headphones" 01_New_Born.mp3
• does not work: mpg321 -o alsa -a "CARD=Headphones" 01_New_Born.mp3
• does not work: gst-play-1.0 --audiosink='alsasink device=sysdefault' 01_New_Born.mp3
• works: mpg321 -o alsa -a default 01_New_Born.mp3
• works: mpg321 -o alsa -a "hw:1,0" 01_New_Born.mp3
• works: gst-play-1.0 --audiosink='alsasink device=default' 01_New_Born.mp3
• works: gst-play-1.0 --audiosink='alsasink device=hw:1,0' 01_New_Born.mp3

Note that setting --gstout-audiodevice to "default" also fails to work, which was surprising given the above test cases. This might be a separate bug!

To conclude. The documentation should:

• clearly state, with an example output, what to specify for --gstout-audiodevice
  • If, for example, aplay -L is kept as a source of information (which obviously does not work for me), it should be made clear which string to extract from that output
• help users to find the correct setting by mentioning the device spec format of "hw:0,0"
• provide usage examples of relevant command line tools to test a setup.
  • at least mention gst-play and mpg321 with examples of their arguments