[pulseaudio-discuss] [WIP] Passthrough support

[Kelly Anderson]

On 03/24/11 18:58, Dark Shadow wrote:
> On Thu, Mar 24, 2011 at 10:50 AM, Anssi Hannula<anssi.hannula at iki.fi>  wrote:
>> On 24.03.2011 16:18, pl bossart wrote:
>>>> It seems that 384k sample rates aren't supported directly in alsa, I did
>>>> some patching to no avail yet.
>>>>
>>>> In any case if the channel count can be specified with passthrough the
>>>> following should work.
>>>>
>>>> paplay --raw --channels=2 --rate=192000 --passthrough File.dts.spdif192khz (
>>>> this works).
>>>>
>>>> paplay --raw --channels=4 --rate=192000 --passthrough File.dts.spdif384khz (
>>>> this fails).
>>>>
>>>> To passthrough dolby true-hd it looks like it'll be necessary for more than
>>>> two channels to work.
>>> There was a thread on dts-hd in alsa-devel at some point. Anssi
>>> (cc:ed) contributed some patches for HDMI and provided the information
>>> below on ffmpeg configurations.
>>> You may want to try at the alsa level before trying with pulseaudio to
>>> make sure your setup is correct. I tend to believe you have to go for
>>> 8ch @ 192kHz to make this work based on my limited understanding of
>>> HBR.
>> Indeed for HBR you need to always specify 8 channels and use rate to
>> control the final rate (i.e. you either use "normal" 2 channel
>> passthrough or HBR 8 channel passthrough).
>>
>> For example to passthrough the abovementioned 384 kHz stream you need to
>> use 8 channels and rate of 96000. However, I think 384kHz DTS bitstream
>> is generally *not* supported by A/V receivers, so you probably want to
>> use 768kHz (8 channels, 192kHz).
>>
>> (note: I haven't tested whether HBR works with pulseaudio or not)
>>
>>
>>> The DTS-HD part is not merged yet (patch is in ffmpeg-devel@), but the
>>> TrueHD and E-AC-3 support is already there in ffmpeg trunk.
>>>
>>> The ffmpeg commandline to use is:
>>> ffmpeg -i input.file -f spdif output.spdif
>>>
>>> For DTS-HD files, to get full passthrough (i.e. not only core), a
>>> -dtshd_rate parameter is needed, which sets the output IEC958 rate.
>>> ffmpeg -i input.file -f spdif -dtshd_rate 192000 output.spdif
>>> ffmpeg -i input.file -f spdif -dtshd_rate 768000 output.spdif
>>> 192000Hz is enough for streams that have a bitrate below 6.144Mbps, which
>>> means all DTS-HD High Resolution Audio files and even many of the DTS-HD
>>> Master Audio (the latter are lossless VBR).
>>>
>>> To play the spdif files back, I use
>>> aplay -D hdmi:CARD=$CARDNAME,DEV=$DEVICENUM,AES0=0x06 -c $CHANCOUNT -r
>>> $RATE file.spdif
>>>
>>> - replacing $CARDNAME with the card name
>>> - replacing $DEVICENUM with 0..3 depending on card and hdmi port (for
>>> non-zero DEVICENUM you'll need a patch from alsa git:
>>> http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=e6d5dcf1f625984605d362338d71162de45a6c60
>>> )
>>> - set $CHANCOUNT and $RATE as per below
>>>   - rate 192000 and channels 2 for IEC958 rate 192 kHz (for e.g. 48 kHz
>>> E-AC-3, and DTS-HD when the IEC958 rate was set to 192000 in ffmpeg)
>>>   - rate 192000 and channels 8 for IEC958 rate 768 kHz (for most TrueHD
>>> files, and for DTS-HD when the rate was set to 768000)
>>> - note that having the 0x02 bit (non-pcm) set in AES0 is mandatory when
>>> $CHANCOUNT is larger than 2, as ALSA uses it to determine whether to use
>>> HBR or not. The additional 0x04 (non-copyright) I use above is not
>>> mandatory, but is the alsa default so I kept it.
>>
>> --
>> Anssi Hannula
>> _______________________________________________
>> pulseaudio-discuss mailing list
>> pulseaudio-discuss at mail.0pointer.de
>> https://tango.0pointer.de/mailman/listinfo/pulseaudio-discuss
>>
> Would anyone know where I could get a hold of some DTS-HD samples in
> 192Khz and 384kHz for testing?

You can extract the dts-hd tracks from your mkv's with mkvextract.  You 
can make them with spdifer (part of AudioFilter).


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