Hi Ethan,
On Thu, Nov 9, 2023 at 5:36 PM Ethan White <ethan@xxxxxxxxxxxxxx> wrote:
>
> On 10/17/23 13:10, Ethan White wrote:
> > Hi,
> >
> > How do I inform Bluez of my a2dp transport delay? The media-api
> > document shows a Delay property for the MediaTransport1 interface but
> > attempts at writing this property yield the following error:
> >
> > org.freedesktop.DBus.Error.PropertyReadOnly: Property 'Delay' is not
> > writable
> >
> >
> > Reviewing profiles/audio/transport.c a2dp_properties (Bluez 5.70) I find
> > that the delay property does not have a set function:
> >
> > line 846: { "Delay", "q", get_delay_reporting, NULL,
> > delay_reporting_exists },
> >
> >
> > What am I missing here? How an I supposed to inform the a2dp source of
> > my playback delay? Thanks for any help.
> >
> > Regards,
> > Ethan
>
> I'm currently using org.bluez.Media1 RegisterEndpoint to expose my a2dp
> sink to a2dp sources. I use org.bluez.MediaTransport1 Acquire to get
> the transport. I can write the 'Volume' property of
> org.bluez.MediaTransport1 to change the audio source volume. However,
> writing to the 'Delay' property of the org.bluez.MediaTransport1
> interface yields only errors as this property appears to be read-only
> despite bluez/docs/media-api.rst showing this property to be read/write.
>
> When using busctl from the host running my a2dp sink to inspect the
> transport I get a dash '-' in place of a numerical value:
> host:~$ busctl introspect org.bluez
> /org/bluez/hci0/dev_xx_xx_xx_xx_xx_xx/fd0
> NAME TYPE SIGNATURE RESULT/VALUE
> FLAGS
> org.bluez.MediaTransport1 interface - -
> -
> .Acquire method - hqq
> -
> .Release method - -
> -
> .TryAcquire method - hqq
> -
> .Codec property y 2
> emits-change
> .Configuration property ay 6 128 1 4 131
> 232 0 emits-change
> .Delay property q -
> emits-change
> .Device property o
> "/org/bluez/hci0/dev_E8_78_65_F2_14_24" emits-change
> .State property s "active"
> emits-change
> .UUID property s
> "0000110b-0000-1000-8000-00805f9b34fb" emits-change
> .Volume property q 64
> emits-change writable
> org.freedesktop.DBus.Introspectable interface - -
> -
> .Introspect method - s
> -
> org.freedesktop.DBus.Properties interface - -
> -
> .Get method ss v
> -
> .GetAll method s a{sv}
> -
> .Set method ssv -
> -
> .PropertiesChanged signal sa{sv}as -
> -
>
> Does Bluez allow an a2dp sink to report its playback delay to the a2dp
> source via the org.bluez.MediaTransport1 Delay property? Is there some
> other way to communicate this delay back to the audio source for proper
> lip-sync with video?
Looks like setting the Delay was never implemented:
https://github.com/bluez/bluez/blob/master/profiles/audio/transport.c#L878
File an issue at github, I don't have time to resolve it right now but
it should be relatively trivial to implement it.
> Regards,
> Ethan
>
>
--
Luiz Augusto von Dentz
