Added start latency param roc-streaming#688

src/internal_modules/roc_audio/latency_tuner.h

@@ -81,6 +81,13 @@ struct LatencyConfig {
     //!  Negative value is an error.
     core::nanoseconds_t target_latency;
 
+    //! Start latency.
+    //! @remarks
+    //!  In case of dynamic latency the tuner will start from this value.
+    //! @note
+    //!  This value makes sense only when target_latency is set to 0.
+    core::nanoseconds_t start_latency;
+
     //! Minimum allowed latency.
     //! @remarks
     //!  If the latency goes out of bounds, the session is terminated.

src/internal_modules/roc_pipeline/receiver_session.cpp

@@ -82,7 +82,11 @@ ReceiverSession::ReceiverSession(
     pkt_reader = filter_.get();
 
     delayed_reader_.reset(new (delayed_reader_) packet::DelayedReader(
-        *pkt_reader, session_config.latency.target_latency, pkt_encoding->sample_spec));
+        *pkt_reader,
+        session_config.latency.target_latency != 0
+            ? session_config.latency.target_latency
+            : session_config.latency.start_latency,
+        pkt_encoding->sample_spec));
     if (!delayed_reader_ || !delayed_reader_->is_valid()) {
         return;
     }

src/public_api/include/roc/config.h

@@ -896,6 +896,13 @@ typedef struct roc_receiver_config {
      */
     unsigned long long target_latency;
 
+    /** Start latency, in nanoseconds.
+     *
+     * If target latency is set to zero, and latency tuning is enabled, this value
+     * sets initial value of latency.
+     */
+     unsigned long long start_latency;
+
     /** Minimum allowed latency, in nanoseconds.
      *
      * How latency is calculated depends on \c latency_tuner_backend field.

src/public_api/src/adapters.cpp

@@ -173,6 +173,18 @@ bool receiver_config_from_user(node::Context&,
             (core::nanoseconds_t)in.target_latency;
     }
 
+    if (in.start_latency != 0) {
+        if (in.target_latency != 0) {
+            roc_log (LogError,
+                    "bad configuration:"
+                    " start latency must be 0 if latency tuning is disabled"
+                    " (target_latency != 0)");
+            return false;
+        }
+        out.session_defaults.latency.start_latency =
+            (core::nanoseconds_t)in.start_latency;
+    }
+
     if (in.min_latency != 0) {
         out.session_defaults.latency.min_latency = (core::nanoseconds_t)in.min_latency;
     }

src/tools/roc_recv/cmdline.ggo

@@ -32,6 +32,9 @@ section "Options"
     option "target-latency" - "Target latency, TIME units"
         string optional
 
+    option "start-latency" - "Start latency, target-latency must be 0 or unset, TIME units"
+        string optional
+
     option "io-latency" - "Playback target latency, TIME units"
         string optional
 

src/tools/roc_recv/main.cpp

@@ -110,12 +110,25 @@ int main(int argc, char** argv) {
             roc_log(LogError, "invalid --target-latency: bad format");
             return 1;
         }
-        if (receiver_config.session_defaults.latency.target_latency <= 0) {
+        if (receiver_config.session_defaults.latency.target_latency < 0) {
             roc_log(LogError, "invalid --target-latency: should be > 0");
             return 1;
         }
     }
 
+    if (args.start_latency_given) {
+        if (!core::parse_duration(
+                args.start_latency_arg,
+                receiver_config.session_defaults.latency.start_latency)) {
+            roc_log(LogError, "invalid --start-latency: bad format");
+            return 1;
+        }
+        if (receiver_config.session_defaults.latency.start_latency < 0) {
+            roc_log(LogError, "invalid --start-latency: should be >= 0");
+            return 1;
+        }
+    }
+
     if (args.min_latency_given || args.max_latency_given) {
         if (!args.min_latency_given || !args.max_latency_given) {
             roc_log(LogError,