RTP player: Doubled buffer for replay to avoid play stop caused by underruns

Patch solves issue for case when QT plays audio faster than reads it from file.
The change looks strange because there is no way how to get buffer size before
starting the play. So code start the play, reads buffer and stop it. Then
increases buffer size and start play again.

Note: You still can receive ALSA notifications like:
ALSA lib pcm.c:8545:(snd_pcm_recover) underrun occurred
but it do not stop audio replay.

1 files changed, 14 insertions, 4 deletions

diff --git a/ui/qt/rtp_audio_stream.cpp b/ui/qt/rtp_audio_stream.cpp
index e0b39f740a..19eb51f3c3 100644
--- a/ui/qt/rtp_audio_stream.cpp
+++ b/ui/qt/rtp_audio_stream.cpp
@@ -622,10 +622,6 @@ void RtpAudioStream::startPlaying()
         emit playbackError(playback_error);
     }
 
-    audio_output_ = new QAudioOutput(cur_out_device, format, this);
-    audio_output_->setNotifyInterval(65); // ~15 fps
-    connect(audio_output_, SIGNAL(stateChanged(QAudio::State)), this, SLOT(outputStateChanged(QAudio::State)));
-    connect(audio_output_, SIGNAL(notify()), this, SLOT(outputNotify()));
     start_pos = (qint64)(start_play_time_ * sample_bytes_ * audio_out_rate_);
     // Round to sample_bytes_ boundary
     start_pos = (start_pos / sample_bytes_) * sample_bytes_;
@@ -634,7 +630,21 @@ void RtpAudioStream::startPlaying()
         start_pos *= 2;
     }
     if (start_pos < tempfile_->size()) {
+        int bufferSize;
+
+        // Start and stop audio with no connection to UI and store buffer size
+        tempfile_->seek(start_pos);
+        audio_output_ = new QAudioOutput(cur_out_device, format, this);
+        audio_output_->start(tempfile_);
+        bufferSize = audio_output_->bufferSize();
+        audio_output_->stop();
+
+        // Start audio again with doubled buffer size, UI is updated
         tempfile_->seek(start_pos);
+        audio_output_->setBufferSize(bufferSize*2);
+        audio_output_->setNotifyInterval(100); // ~15 fps
+        connect(audio_output_, SIGNAL(stateChanged(QAudio::State)), this, SLOT(outputStateChanged(QAudio::State)));
+        connect(audio_output_, SIGNAL(notify()), this, SLOT(outputNotify()));
         audio_output_->start(tempfile_);
         emit startedPlaying();
         // QTBUG-6548 StoppedState is not always emitted on error, force a cleanup