[LAD] JACK latency API clarifications

Paul Davis paul at linuxaudiosystems.com
Thu Feb 20 22:45:50 UTC 2014

On Thu, Feb 20, 2014 at 5:32 PM, Stefano D'Angelo <zanga.mail at gmail.com>wrote:

> Hi all,
> Let's say I have a client that introduces an amount of latency that's
> variable at runtime and potentially unbounded. From JACK's docs it
> seems that you need to recompute the min/max latencies in the latency
> callback that's called "by the server" whenever it feels like, but you
> can force that by calling jack_recompute_total_latencies (right?).
> The problem is, you are advised to call this last function only after
> calling jack_port_set_latency_range(), which you should only call in
> the latency callback, which may be called next month... am I dumb
> (probably) or is there a deadly loop?

the latency callback will be issued (twice, once for upstream, once for
downstream) after one of two things happens:

   * the graph changes
   * a client calls jack_recompute_total_latencies()

you would call the latter if something happens that alters your clients own
latency (e.g the change to some parameter of an algorithm that causes your
client to change its latency). then you wait for the latency callback and
reset your port latencies.
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