Hi Luiz, First things first, many thanks for your comments! On Wed, May 25, 2016 at 7:32 PM, Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx> wrote: > Hi Harry, > > On Wed, May 25, 2016 at 4:13 AM, Qingtao Cao <qingtao.cao.au@xxxxxxxxx> wrote: >> Hi Community, >> >> I have two questions about how bluez would invoke the >> SelectConfiguration provided by the registered media endpoint. I am >> using bluez-4.101. >> >> 1. With a bluetooth speaker that supports A2DP, from logs of my >> program manipulating bluez's dbus API I saw bluez had invoked the >> SelectConfiguration method with parameters describing the capability >> of the bluetooth speaker, so that my program could send back bluez a >> dbus message with my preferred settings, e.g., 48k Hz frequency and >> Mono. > > SelectConfiguration is only called in case of outgoing connection so > you can select the preferred configuration, for incoming connection > the remote will select the configuration so we can only accept or > reject it. > So do you mean that the SCO connection with a bluetooth headset will be regarded as incoming instead of outgoing, despite that there are both speaker and mic on it? >> However, when I tested with a bluetooth headset that only supports >> HFP/HSP, bluez seems not calling SelectConfiguration, but >> SetConfiguration directly. Furthermore, the "Configuration" in the >> parameters of the SetConfiguration is an empty array: >> >> object path "/org/bluez/3765/hci1/dev_1C_48_F9_AD_19_EE/fd5" >> array [ >> dict entry( >> string "Device" >> variant object path >> "/org/bluez/3765/hci1/dev_1C_48_F9_AD_19_EE" >> ) >> dict entry( >> string "UUID" >> variant string "0000111f-0000-1000-8000-00805f9b34fb" >> ) >> dict entry( >> string "Codec" >> variant byte 0 >> ) >> dict entry( >> string "Configuration" >> variant array [ >> ] >> ) >> dict entry( >> string "NREC" >> variant boolean true >> ) >> dict entry( >> string "InbandRingtone" >> variant boolean true >> ) >> dict entry( >> string "Routing" >> variant string "HCI" >> ) >> ] > > Hmm Im afraid this is old since we no longer support HSP/HFP > endpoints, the reference implementation of HFP is in ofono which does > have its own interface to setup the audio and pulseaudio has also its > own implementation for HSP. > > If you are using ofono these are the interfaces involved: > > http://git.kernel.org/cgit/network/ofono/ofono.git/tree/doc/handsfree-audio-api.txt > Thanks for your information! I am currently using bluez-4.101 and there is no support for ofono yet. >> I am wondering if this is the reason that makes bluez not calling >> SelectConfiguration for such bluetooth headsetl in the first place, >> since it is not configurable at all. >> >> Please confirm whether this is how bluez works. >> >> Then how can I further know the frequency and the number of channel >> supported by my bluetooth headset? (from my testing with different wav >> files it seems only plays well format of S16_LE, 8kHz, mono) > > HFP/HSP should be always mono, and in case of CVSD it is 8 kHZ, only > when using SBC that 16 Khz is used but contrary to A2DP in HFP there > is no codec configuration so these parameter are fixed per codec. > Ok, do you mean that with HFP/HSP, if the voice codec is CVSD then the input PCM must have a sample rate of 8KHz, Mono, and since this is fixed per voice codec bluez simply skips over invoking the SelectConfiguration callback function provided by the registered HFP_AG_UUID media endpoint? Moreover, for bluez4 and bluetooth 3.0 spec, the voice codecs seems to be just CVSD, A-law and u-law, if I changed my voice settings of the hciX interface to use A-law or u-law, then what's the respective sample rate required on input PCM? >> >> 2. For my bluetooth speaker that is configurable on frequency and the >> number of channel, if I specify a particular configuration, then it >> won't support other wave files with different configurations. For >> example, if I specify the sample rate used by it to be 48k Hz, but I >> play a wav file of 8k Hz instead, then it will be played 6 times >> faster than expected, only a short screaming is heard. > > You will need to resample it if the output should be in 48 Khz. > >> Moreover, during testing I found that if I specify more than one bit >> for frequency or channel_mode for example in the return message of >> SelectConfiguration, the connection will simply fail. >> >> So, does this mean my program, or the audio server, would have to >> convert the format of sound files to the frequency, channel_mode etc >> used by the remote bluetooth configured through SelectConfiguration >> before playing sound files? > > Yes, that is one of the main features of an audio server should deal > with, but instead of reinventing the wheel you could use pulseaudio > since it already takes cares of these details for you. > Yeah, I will certainly do that when needed. Currently I am trying to modify the simple C program in this post (http://www.lightofdawn.org/blog/?viewCat=Bluetooth) to better understand how to manipulate bluez's DBUS API directly to stream audio packets instead of using obsolete bluez's plugin for alsa :-) Thanks again! Harry > -- > Luiz Augusto von Dentz -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
