I recently updated my AppleTV from a v2 to a v4, as well as replaced three older Airport Expresses with the newest version that supports Airplay 2. This was done because iTunes 12 seems to have problems streaming audio to a mixed Airplay 1&2 environment. Also, I wanted to make everything HomeKit compatible. After the update the streaming issues were gone, but a new problem surfaced. Whereas the old AppleTV never had problems staying in sync, the new ATV is about 1/8 second ahead (not behind as other people have found when connected to certain brands of television), just enough to create an echo when streaming multiroom audio.
The ATV4 is connected similarly to the ATV2, with video going to a 1080p projector and audio sent to an older analog stereo system via an d/a converter. The only difference is that the ATV4 lacks an audio output, so I installed an HDMI splitter to extract the audio before it's sent to the projector. That doesn't seem to be a factor however, as the music is also out of sync if I play it through the projector's internal speaker.
The question is, what's the deal with Airplay 2 sync, and how does ATV adjust for system audio delays? I was under the impression that Airplay 2 was pretty good at this.
Is there a way I can adjust the sync manually? Some TVs allow for this, but I'm not going through a TV. Perhaps that's the problem, but my setup doesn't seem so unusual.