RPi4 testbuild with HD audio passtrhough (Atmos etc)

  • HiassofT thank you very much for the info, looks like I didn't carefully read the thread. Is the master branch also limited to HD on RPI4?

  • Yes, master is still limited to HD. 4k will come later, it's currently not supported in the RPi video driver.

    so long,


  • Ok,

    then I can say that I'm testing this and I've been able to get FullHD but there's a problem with hmm not sure what exactly.

    After about 11-12 mins of playback DTS-HD MA Atmos the sounds starts to hickup AVR is blinks but the video is still there.

    In the debug.log the only thing that is printed is this line:

    ERROR <general>: CAESinkALSA - snd_pcm_writei(-32) Broken pipe - trying to recover

    right now I'm trying to play with this hint but can't say much only that after applying the fix, the error is gone. Yet the hiccups are still there and are more aggressive with the time. To fix this it's enough to stop and resume playback.

    Fix for HDMI sound dropouts - snd_pcm_writei(-32) Broken pipe

    In the beginning the problem could be easily seen just after few mins, but then I've recalled the problem with RPI4 and USB3 transfer rates slowdowns. I've been able to use this hint:

    STICKY: If you have a Raspberry Pi 4 and are getting bad speeds transferring data to/from USB3.0 SSDs, read this - Raspberry Pi Forums

    which improved things a lot and now the problem occurs as I mentioned in the beginning which is around 11-12 mins.

    I may be of course wrong but it kind of looks like it's some kind of buffer issue. The DTS-HD MA requires quite a lot of bandwidth during some extensive action, from what I've found it can be up to 24.5Mbps now if we add there also requirement for video then it if RPi4 has real USB 3 transfer issues, it really look like it could be an issue that's causing the problem.

    I'll see if I can get some different chassis for the drive that doesn't need a quirk if I'll test this I'll of course put the info here.

  • My understanding is that HDMI 1.4 audio has a max spec of 8 channels of 192kHz / 24 bit uncompressed PCM audio - which gives a max audio output bit rate of :

    8 x 192000 x 24 = ~ 36.9Mbs

    I guess any buffering for HDMI audio should be considering that as the top audio bitrate that HDMI can carry?

    My understanding is that 8 x 192 x 24 is also the spec that is required for lossless compressed HD Audio to be carried over HDMI - which is why the Raspberry Pi 3B+ and earlier can't carry HD Audio - as they could only carry 4 x 192 x 24 bit (or 8 x 96 x 24 bit) which doesn't guarantee enough bitrate for the peaks of HD Audio lossless compressed content (which may not compress hugely on very complex content?)

    Dolby True HD and DTS HD MA sound tracks are usually lossless compressed 8 channels at 48k 24 bit (some are 96k and a very small number are 192k) which gives an uncompressed bitrate of around 9Mbs (or 18Mbs if 96kHz is used), however releases like Akira can contain 6 channel 192k 24 bit tracks (and 8 channel is theoretically allowed).

    For very complex audio the lossless compression used by DTS HD MA and Dolby True HD may not deliver huge bandwidth savings - and if you add in Atmos and DTS:x data as well on newer tracks this will also increase the bitrate a bit I guess?

  • Hi all,

    I just saw here that Kodi 19.0 was released and that librelec and other Kodi centric distributions were going to be updated too but I did not see any details on features like HD audio passthrough and UHD/4k resolution support.

    Does anyone know if those features are going to be supported in Kodi 19 on RPi4 ?

  • Froggy please read this topic and also this one:

    Nightly builds Rpi4 Audio passthrough TrueHD/Master HD not working (huge stutter) anymore

    In general, the test builds of libreelec are capable of handling 4k uhd, atmos passthrough but there are still some issues.

    Yes. Worth pointing out that the only codec supported at 4K UHD is h.265/HEVC (h.264/AVC is still only supported for 1080p (*)) and that a lot of UHD h.265/HEVC content is also HDR10.

    HDR replay is still very much a work-in-progress on the Pi 4B. They have HDR modes being triggered on TVs (i.e. the HDMI signals an HDR10 or HLG EOTF) but they have still got issues flagging Rec 2020 instead of Rec 709 primaries (so images look less colourful), and the output of 10-bit video is still 8-bit RGB (so you will potentially see banding, which 10-bit is designed to minimise)

    (*) h.264/AVC decoding is handled by the legacy video decoder module that is largely the same as that on the previous generations of Pi, h.265/HEVC support was added via a separate module. (MPEG2 and VC-1 support is now software only, as the Pi foundation don't offer hardware decode licences for these codecs for the Pi 4B)

  • Hi,

    I cross-post here :

    I tested the 9.95.1 Kodi 10 beta with 2 contents :

    - 1 UHD h265 Dolby True HD 7.1 audio

    - 1 UHD h265 DTS True HD Master

    It works perfectly !

    Thanks to all developpers and contributors : You have done a great job ! ;)

  • I tried 9.95.1 Kodi 10 beta on my RPi400, but I was unable to get frame packed 3D to work. I have 3D MVC MKV files that work perfectly on an older version of Kodi on my RPi3. Is MVC no longer supported?

  • Extreme bummer..

    So no it isn't and it seems all the forum crawling I've been doing doesn't seem to give any hope to those wanting a Raspberry Pi 4 to do frame packed 3D MVC formatted files.

    I saw a mention of LE 9.2.6, but no conclusive evidence that it does beyond half frame TAB/SBS 3D.

    Suppose I'll give it a try on my RPi400 and cross my fingers...

  • Extreme bummer..

    So no it isn't and it seems all the forum crawling I've been doing doesn't seem to give any hope to those wanting a Raspberry Pi 4 to do frame packed 3D MVC formatted files.

    I saw a mention of LE 9.2.6, but no conclusive evidence that it does beyond half frame TAB/SBS 3D.

    Suppose I'll give it a try on my RPi400 and cross my fingers...

    I think the LE 9.2.6 reference was for Pi3B+ and earlier models, because it uses the legacy, and bespoke?, video decoder sub-systems that were supported on the Pi 3B+ and earlier that supported MVC decode. (Not sure if 1080p24 frame packed HDMI output is linked or separate to that)

    AIUI the Pi 4B has never supported the legacy approaches, and the newer Pi 3B+ and earlier builds using the new video structures don't support them either, as they both use the mainline V4L2 approach.

  • I'm really grateful for the HD audio passthrough on the new official releases! Thanks for your great work everybody. I have not had any issues yet. Some of the video have a bit choppy playback now (>30gb 1080p BD dumps) but the sound is always fine.

  • Hi,

    I am pretty new here, I hope I found the right topic to post this… I have beta3 installed on an RPI4 and everything works fine except TrueHD Passthrough. The Pi is plugged directly into an Atmos capable Samsung soundbar, when playing a truehd file, absolutely no audio is played. Everything else (incl DD+) works fine, also libreelec 9.2.6 passes TrueHD with no problems to the soundbar.

    Is this known or maybe is there a solution also?

    Many thanks in advance!

  • Libreeelec 9.2.6 does not support TrueHD passthrough (or DTS-HD) on Pi.

    It should be supported on LE 10 beta.

    Are you quite sure your soundbar supports TrueHD passthrough? Do you have a link to the specs?