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AV Sync issues - Firestick sync HDR Dolby Digital HDMI (SOLVED)

(Topic created on: 03-02-2023 01:55 PM)
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erew
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I'm using a Samsung sound bar with a TV and a firestick and have all sorts of audio sync issues when using Dolby digital output. The AV sync, although set in the firestick settings, would change between different media.

I have to say, I don't believe this is a Samsung issue specifically, but perhaps all devices that may use HDR over HDMI 2.0 (not HDMI 2.1)..... so older TV's etc. In my case, I struggled with a Firestick 4k and the audio sync settings required, changing from one type of media to another. I've seen other posts on this forum and wonder if others have this issue too, so thought Id post. 

I found what appears to be a permanent fix!

My setup is Firestick 4k plugged into > TV > Soundbar (HDMI ARC connection)

I also tried optical from the TV to the soundbar and the same issue occurred. 

**TLDR** change the firestick "Dynamic Range Settings" to "Always HDR", rather than "Adaptive". This will keep the audio sync standardized across all apps on the firestick and sound bars or amplifiers linked to the firestick.

PROBLEM EXAMPLE
You play a film that is HDR and Dolby Surround on a TV system that *IS* HDMI 2.0 standard (18Gbps max). Because of the bandwidth limitation you need to change the AV Audio sync so the audio arrives before the image. This works great....Until....

You go to the Youtube app or something that is a NON-HDR image OR just uses standard stereo/PCM. All of a sudden the AV Sync is all wrong again. The audio is 1-2 seconds ahead of the on screen image.

The reason being, NON-HDR content and Stereo (or PCM) requires less bandwidth, as such there is no delay with ALL the image and audio data arriving on time at the TV. So all of a sudden the audio is therefore out of sync again and you have to re-adjust it for that app, or you just think your firestick/sound system is rubbish and give up on Dolby 5.1 or greater......

EXPLANATION (as simple as I can put it here)
When a firestick "Dynamic Range Settings" is on "Adaptive" it switches the image between Standard and HDR as it feels necessary. So a film on Netflix/Prime/Disney etc will typically play as HDR content (if your TV supports its etc) utilizing MORE of the HDMI 2.0 bandwidth. Apps like Youtube or where the content isn't HDR, will switch to a standard image, using LESS of the HDMI 2.0 bandwidth.

The issue comes in when you use a Dolby Digital 5.1 or greater standard. The image "Standard VS HDR" switching can alter the available bandwidth for audio, causing what I will describe as a race/slowdown/sync variability issue.

If you set ALL display output to "Always HDR" then even NON-HDR will be sent out as the HDR standard, so it always consumes the same amount of bandwidth, therefore always requiring the same audio delay (about 4x dots away from the right side end of the AV-Sync firestick app......in my tests at least).

I cant speak to if there are other audio delays on HDMI 2.1 equipment, there could be delays introduced elsewhere in the audio processing that setting all content to Always HDR *may* resolve, by keeping a consistent amount of data always flowing. My HDMI 2.0 TV does seem to have this issue for sure though.

OTHER FIXES

- Amazon could create a change to the AV Sync app, to change the delay based on what the "Adaptive" "Dynamic Range Settings" are doing. e.g. no delay for Standard/StereoPCM and delay for HDR content.

- Upgrade your TV etc to one that supports HDMI 2.1, which has a 48Gbps rather than the HDMI 2.0 18Gbps standard.

- If you're happy with no surround sound, switch to Stereo/PCM on the Firestick or other device.

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