On 9 March 2015 at 15:41, Thomas Martitz <kugel at rockbox.org> wrote: > Am 08.03.2015 um 12:42 schrieb Alexander E. Patrakov: > >> 08.03.2015 13:54, Xamindar wrote: >>> >>> Further testing has shown that this is a pulseaudio problem. When I have >>> my audio device set to "Digital Surround 7.1" as it should be, >>> passthrough will not work in any app I test (kodi and vlc). My options >>> are here in this image: http://i.imgur.com/3zkMsGy.png >>> I do have the passthrough settings checked as can be seen in this image: >>> http://i.imgur.com/N7KMCZc.png >>> >>> If I downgrade my settings to the "Digital Stereo" option then >>> passthrough will work for some reason. >>> >>> Is this a limitation/regression in pulseaudio? Or do I simply have some >>> configuration set wrong? >> >> >> This is a limitation and not a regression (i.e. passthrough never worked >> on non-stereo sinks). Here is what happens. >> >> Passthrough works this way: an application negotiates a format with >> PulseAudio, and then sends a fake stereo stream that contains encoded data, >> just what would have to be transferred over spdif. Then PulseAudio is >> supposed to copy this fake stereo data to the receiver. >> >> So, it would need to open the ALSA device in stereo mode. But, in >> multichannel profiles, it opens the ALSA device with the number of channels >> other than 2. So, to support your use case, new logic has to be added to the >> sink code so that it opens audio device with 2 channels and exposes 2 >> channels while in passthrough mode, even if it would use a different channel >> count otherwise. >> >> What fails in your testcase is the line above the "rate update failed, or >> other parts of sample spec didn't match" comment in src/pulse/sink.c (the >> fake channel count doesn't match, as explained above). >> >> But, why are you using the passthrough mode at all? HDMI, unlike SPDIF, >> has enough bandwidth to pass the 7.1 PCM stream. For SPDIF, passthrough was >> a necessity due to this bandwidth limitation. For real HDMI (as opposed to >> HDMI-to-SPDIF converter that doesn't support multichannel PCM anyway), it >> only serves marketing purposes (i.e., in theory, provides no benefits over >> software decoding and sending the resulting multichannel PCM stream). I >> sometimes think that the proper fix is to disallow passthrough completely >> for multichannel HDMI profiles, i.e. to effectively hide the checkboxes that >> you have demonstrated on the screenshot. >> > > > 1) You might want to decode Dolby Digital / DTS on an external receiver > because decoding on the PC requires a license. > 2) Receivers might only accept spdif-data (plain stereo or encoded) > regardless of HDMI's theoretical capabilities. > > If PA is actually unable to pass through in multichannel profiles, then yes, > pavucontrol should not show the check boxes, or better yet grey them out > with a "Change to stereo profile" tooltip. Probably less effort than that to just reopen for 2 channels in passthrough mode. I'll try to get to this soon. -- Arun
