AAC 5.1 - Out of sync and frame hitches

[fidgetymo]

Hello,

I have problems with AAC 5.1 playing out of sync and with frame drops/skips every 5 to 10 seconds or so.
I'm using a ugoos am6b+ with the latest CE p3i and PM4K - however this issue, from my memory, has been present on all coreelec (nightly,cpm+variants).
The ugoos connects > AVR > LG TV.
I've tried LAV full on/off with alternate seek settings on/off.
If I turn off hardware acceleration in CE then it fixes it - not ideal.
If I avoid AAC 5.1 then everything else plays fine - not ideal when I just want to hit play.
I've tried different HDMI devices within CE display settings to no avail.

It hasn't been the worst to avoid AAC 5.1 or force transcodes to AC3 if necessary, and I figured there would be a simple fix that would show up in my research.

But I haven't been able to fix it so I'm wondering if anyone else has experienced this or has a suggestion to try. I haven't been able to find shared experiences through my own research so I'm not hopeful.

[sek111111]

So I just tried an AAC 5.1 file on my setup

P3i T1, ugoos am6b+ > denon x1800h avr > lg c3

and I am not seeing any issues. In Settings>System>Audio I have

In Settings>System>Coreelec I have "Set type of correction to fix audio issues" set to off, and I have "Use alternate seek" enabled in pm4k settings.

If you're having issues with this (what avr do you have?) then another option is to set the number of channels to 2.0, and then enable "Enable Dolby Digital (AC3) Transcoding", though you'd be losing surround this way.

[fidgetymo]

Thanks for checking your setup and providing your settings for reference. I have a Sony STR-AN1000. Yeah I would prefer not to lose surround as you mentioned. I will try fiddling around again once pannal releases T2 if his update doesn't fix it.

[pannal]

This edge case might be fixed with T2.

[fidgetymo]

thanks pannal, i'll look forward to testing and report back.

[pannal]

You can join the Discord channel mentioned in the README and test a T2_dev preview build!

[fidgetymo]

ok good to know, i'll try to test it.

[pannal]

You gotta join first, I have a test build ready for you :)

[pannal]

Added a link in my previous comment so you can easily find it.

[fidgetymo]

Figured I would update this thread with what I understand.

Some HEVC files use a legal but irregular frame-timing pattern.
On Amlogic devices, Kodi’s amcodec hardware decoder does not smooth this timing, so audio (AAC 5.1) and video start out misaligned and Kodi repeatedly resynchronizes them, causing constant A/V offset and small, repeatable video hitches.

The files are not corrupted and play fine on native Plex app on an LG TV and also in software decode as disabling Amlogic hardware acceleration (amcodec) avoids the broken timing path and fixes playback.

As a workaround, it may be possible to create a script that disables the amlogic hardware acceleration and map it to a remote button so it can be toggled outside of playback when needed - I will look into this when I have time.

I've asked @pannal if it's possible to add a toggle to PM4K for this within the files detail screen so acceleration can be disabled per-file. Understandably it's not a priority as the consensus may be that this is an edge case manifested by lower quality source files. However I suspect it could be useful for other cases where software decoding may be preferable, however unlikely.