Latency using HQPlayer Embedded (hqplayerd)

[stefano_mbp]

In the last days I installed and tried HQPlayer Embedded on my server.
As it is an Upnp client I could use it as a renderer, Minimserver is the upnp server and Lumïn app the control point (using Bubbleupnpserver for Lumïn app OpenHome compatibility)
Everything works fine, the sound quality from hqplayerd is really fantastic but I faced an unexpected issue with gapless, most of the times there is a lag between tracks and this is unacceptable.
I reported the issue to Jussi Laako ( info@signalyst.com ) and he answered that the issue is due to the delay with which Minimserver/Java provides the tracks to hqplayerd, he himself had the very same issue using Minimserver.
It must be said that I was transcoding Alac and flac files to wave (hqplayerd doesn’t support Alac format) then I removed transcoding but the issue was still there playing flac files.
Is there anything that can be done to solve this issue? ... perhaps you could work with Jussi to deeper analyze this issue.
It may be useful to know that the problem does not exist using mpd / upmpdcl or JRiver configured as dlna client.
Thank you

[simoncn]

Transcoding always creates a slight delay in starting to stream the data. For gapless playback, the control point/renderer must request the next track a short time before the previous track has finished playing. If the control point/renderer doesn't request the next track soon enough, playback will not be gapless.

With the OpenHome protocol, the renderer makes the request for the next track based on the playing queue information that it holds. Without the OpenHome protocol, the control point and renderer exchange protocol messages to make this happen.

Does hqplayerd support the FLAC format? If so, you can remove MinimServer transcoding and stream FLAC files with no delay. It sounds like you have tried this and there is still a problem. In this case, MinimServer would not be causing the issue.

To narrow down the cause of the problem, please try removing BubbleUPnPServer and using BubbleUPnP instead of the LUMIN app. Do you still have the problem when you do this?

[stefano_mbp]

Thank you Simon, I’m on iPad/iPhone only but tried using MConnect that bypass Bubbleupnpserver too, the gapless issue, with not transcoded flac, is still there ...

[simoncn]

What platform are you using to run MinimServer? Unless it has a very slow CPU or HDD or is accessing the music library across a network, I don't see how latency could be an issue with untranscoded FLAC.

[stefano_mbp]

It runs on a Nuc8i3/16GB ram/Ubuntu 20.04 and on a MacBook Pro i7/16GB ram late 2011, the issue occurs using both. Ubuntu and MacOS High Sierra run both from ssd.
To narrow down the cause of the issue I’ve just tried to play same files transcoded to wave by Minimserver with different resampling rates: 16/44.1 files can be played gapless resampling them in hqplayerd up to 24/176.400, beyond this gapless is broken

[stefano_mbp]

... files are on usb connected hdd for nuc8i3 and on thunderbolt connected hdd for MacBook Pro, they are two identical copies.

[simoncn]

All this points to the issue being with hqplayerd. For FLAC to WAV transcoding in MinimServer/MinimStreamer, the latency increases with output resolution and there is nothing that can be done to prevent this. Other renderers don't have this problem with gapless, so it seems that the implementation of gapless in hqplayerd is over-sensitive to latency.

[stefano_mbp]

That’s my idea too, it seems that as the resolution increases, the request arrives later and later ... so maybe a problem in the buffer management, the higher the resolution the shorter the time remaining in the buffer

[simoncn]

Yes, I think the solution is likely to be for hqplayerd to use a larger buffer. Adding buffering on the MinimServer side would increase the delay.

[simoncn]

I have been doing some detailed analysis of what is happening. The primary cause of the problem is that HQPlayer Embedded does not implement the UPnP protocol for gapless playback. I will post more details here soon.