Timeout when writing output samples throughout the audio pipeline

This allows the audio pipeline to remain responsive even when the drain
buffer has completely filled. This in turn means that you now see the
track info in the 'now playing' screen change if the current track
changes whilst you are paused.

Since I was fucking around a lot in the audio processor anyway, I also
added mono->stereo expansion so that playing mono tracks on Bluetooth no
longer destroys your ears.

1 files changed, 40 insertions, 6 deletions

diff --git a/src/tangara/audio/audio_decoder.cpp b/src/tangara/audio/audio_decoder.cpp
index ee06d984..992444f0 100644
--- a/src/tangara/audio/audio_decoder.cpp
+++ b/src/tangara/audio/audio_decoder.cpp
@@ -48,7 +48,7 @@ static const char* kTag = "decoder";
  * increasing its size.
  */
 static constexpr std::size_t kCodecBufferLength =
-    drivers::kI2SBufferLengthFrames * sizeof(sample::Sample);
+    drivers::kI2SBufferLengthFrames * 2;
 
 auto Decoder::Start(std::shared_ptr<SampleProcessor> sink) -> Decoder* {
   Decoder* task = new Decoder(sink);
@@ -78,11 +78,17 @@ Decoder::Decoder(std::shared_ptr<SampleProcessor> processor)
  * Main decoding loop. Handles watching for new streams, or continuing to nudge
  * along the current stream if we have one.
  */
+IRAM_ATTR
 void Decoder::Main() {
   for (;;) {
-    // Check whether there's a new stream to begin. If we're idle, then we
-    // simply park and wait forever for a stream to arrive.
-    TickType_t wait_time = stream_ ? 0 : portMAX_DELAY;
+    // How long should we spend waiting for a command? By default, assume we're
+    // idle and wait forever.
+    TickType_t wait_time = portMAX_DELAY;
+    if (!leftover_samples_.empty() || stream_) {
+      // If we have work to do, then don't block waiting for a new stream.
+      wait_time = 0;
+    }
+
     NextStream* next;
     if (xQueueReceive(next_stream_, &next, wait_time)) {
       // Copy the data out of the queue, then clean up the item.
@@ -103,8 +109,15 @@ void Decoder::Main() {
 
       // Start decoding the new stream.
       prepareDecode(new_stream);
+
+      // Keep handling commands until the command queue is empty.
+      continue;
     }
 
+    // We should always have a stream if we returned from xQueueReceive without
+    // receiving a new stream.
+    assert(stream_);
+
     if (!continueDecode()) {
       finishDecode(false);
     }
@@ -167,16 +180,36 @@ auto Decoder::prepareDecode(std::shared_ptr<TaggedStream> stream) -> void {
 }
 
 auto Decoder::continueDecode() -> bool {
+  // First, see if we have any samples from a previous decode that still need
+  // to be sent.
+  if (!leftover_samples_.empty()) {
+    leftover_samples_ = processor_->continueStream(leftover_samples_);
+    return true;
+  }
+
+  // We might have already cleaned up the codec if the last decode pass of the
+  // stream resulted in leftoverr samples.
+  if (!codec_) {
+    return false;
+  }
+
   auto res = codec_->DecodeTo(codec_buffer_);
   if (res.has_error()) {
     return false;
   }
 
   if (res->samples_written > 0) {
-    processor_->continueStream(codec_buffer_.first(res->samples_written));
+    leftover_samples_ =
+        processor_->continueStream(codec_buffer_.first(res->samples_written));
+  }
+
+  if (res->is_stream_finished) {
+    // The codec has finished, so make sure we don't call it again.
+    codec_.reset();
   }
 
-  return !res->is_stream_finished;
+  // We're done iff the codec has finished and we sent everything.
+  return codec_ || !leftover_samples_.empty();
 }
 
 auto Decoder::finishDecode(bool cancel) -> void {
@@ -191,6 +224,7 @@ auto Decoder::finishDecode(bool cancel) -> void {
   processor_->endStream(cancel);
 
   // Clean up after ourselves.
+  leftover_samples_ = {};
   stream_.reset();
   codec_.reset();
   track_.reset();