[pulseaudio-discuss] review+pull-request: Passthrough support

Arun Raghavan arun.raghavan at collabora.co.uk
Wed Apr 20 20:59:17 PDT 2011

On Tue, 2011-04-19 at 15:03 -0500, pl bossart wrote:
> I finally managed to figure out why eac3 wouldn't work in passthrough
> mode. Apparently my HDMI receiver will only lock on eac3 data if the
> AES0 control is set to 0x06 (non-audio, ie iec61937).
> ffmpeg -acodec copy -i csi_miami_5.1_256_spx.eac3 -f spdif outfile.pcm
> aplay -Dhdmi:AES0=0x6 -fs16 -c2 -r192000 outfile.pcm
> the same file plays well through pulseaudio if I modifed default.conf to
> [Mapping hdmi-stereo]
> device-strings = hdmi:%f,AES0=0x06
> channel-map = left,right
> priority = 4
> direction = output
> Somehow we need to find a way to set this AES0 byte when opening the
> iec958 or hdmi device in the passthrough code, and reset it back to
> 0x04 for PCM playback (should be fairly easy to do by looking at the
> code of iecset in alsa-utils). Beats me why this was not needed for
> plain ac3, but setting the audio bit is actually the correct thing to
> do.

If my reading is correct, this is something we should do for all formats

> So far all the tests seem ok with the ffmpeg examples, with the
> exception of two files:
> - 7_pt_1: works well with ffmpeg, aplay but the sound is way too fast
> with pulseaudio. Lots of rewind messages seen in PulseAudio.
> - serenity_english_5.1_1536.eac3 file: no sound out, and again lots of
> rewind messages (the receiver still shows the D+ logo though). The
> same file converted with ffmpeg and played with aplay seems fine.
> looks like a buffering issue more than a payloader problem really.

Is the ALSA device correctly being configured to 192 kHz?

-- Arun

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