Fix (i think?) mysterious overly large reads in libmad

src/audio/audio_task.cpp

@@ -173,11 +173,11 @@ void AudioTaskMain(std::unique_ptr<Pipeline> pipeline, IAudioSink* sink) {
       float samples_sunk = bytes_sunk;
       samples_sunk /= pcm.channels;
 
-      int8_t bps = pcm.bits_per_sample;
+      // Samples must be aligned to 16 bits. The number of actual bytes per
-      if (bps == 24) {
+      // sample is therefore the bps divided by 16, rounded up (align to word),
-        bps = 32;
+      // times two (convert to bytes).
-      }
+      uint8_t bytes_per_sample = ((pcm.bits_per_sample + 16 - 1) / 16) * 2;
-      samples_sunk /= (bps / 8);
+      samples_sunk /= bytes_per_sample;
 
       current_sample_in_second += samples_sunk;
       while (current_sample_in_second >= pcm.sample_rate) {

src/audio/fatfs_audio_input.cpp

@@ -9,6 +9,7 @@
 
 #include <algorithm>
 #include <chrono>
+#include <cstddef>
 #include <cstdint>
 #include <future>
 #include <memory>
@@ -71,8 +72,7 @@ auto FatfsAudioInput::OpenFile(const std::string& path) -> bool {
   database::TrackTags tags;
   if (!tag_parser.ReadAndParseTags(path, &tags)) {
     ESP_LOGE(kTag, "failed to read tags");
-    tags.encoding = database::Encoding::kFlac;
+    return false;
-    // return false;
   }
 
   auto stream_type = ContainerToStreamType(tags.encoding);
@@ -115,6 +115,8 @@ auto FatfsAudioInput::NeedsToProcess() const -> bool {
 
 auto FatfsAudioInput::Process(const std::vector<InputStream>& inputs,
                               OutputStream* output) -> void {
+  // If the next path is being given to us asynchronously, then we need to check
+  // in regularly to see if it's available yet.
   if (pending_path_) {
     if (!pending_path_->valid()) {
       pending_path_ = {};
@@ -133,11 +135,15 @@ auto FatfsAudioInput::Process(const std::vector<InputStream>& inputs,
     return;
   }
 
+  // If the output buffer isn't ready for a new stream, then we need to wait.
   if (!has_prepared_output_ && !output->prepare(*current_format_)) {
     return;
   }
   has_prepared_output_ = true;
 
+  // Performing many small reads is inefficient; it's better to do fewer, larger
+  // reads. Try to achieve this by only reading in new bytes if the output
+  // buffer has been mostly drained.
   std::size_t max_size = output->data().size_bytes();
   if (max_size < output->data().size_bytes() / 2) {
     return;
@@ -148,6 +154,7 @@ auto FatfsAudioInput::Process(const std::vector<InputStream>& inputs,
       f_read(&current_file_, output->data().data(), max_size, &size);
   if (result != FR_OK) {
     ESP_LOGE(kTag, "file I/O error %d", result);
+    output->mark_producer_finished();
     // TODO(jacqueline): Handle errors.
     return;
   }
@@ -155,6 +162,15 @@ auto FatfsAudioInput::Process(const std::vector<InputStream>& inputs,
   output->add(size);
 
   if (size < max_size || f_eof(&current_file_)) {
+    // HACK: In order to decode the last frame of a file, libmad requires 8
+    // 0-bytes ( == MAD_GUARD_BYTES) to be appended to the end of the stream.
+    // It would be better to do this within mad.cpp, but so far it's the only
+    // decoder that has such a requirement.
+    if (current_container_ == database::Encoding::kMp3) {
+      std::fill_n(output->data().begin(), 8, std::byte(0));
+      output->add(8);
+    }
+
     f_close(&current_file_);
     is_file_open_ = false;
     has_prepared_output_ = false;

src/codecs/include/mad.hpp

@@ -48,7 +48,7 @@ class MadMp3Decoder : public ICodec {
 
   int current_sample_;
 
-  auto GetInputPosition() -> std::size_t;
+  auto GetBytesUsed(std::size_t) -> std::size_t;
 };
 
 }  // namespace codecs

src/codecs/mad.cpp

@@ -13,6 +13,7 @@
 #include "mad.h"
 
 #include "codec.hpp"
+#include "esp_log.h"
 #include "result.hpp"
 #include "types.hpp"
 
@@ -43,9 +44,13 @@ MadMp3Decoder::~MadMp3Decoder() {
   mad_synth_finish(&synth_);
 }
 
-auto MadMp3Decoder::GetInputPosition() -> std::size_t {
+auto MadMp3Decoder::GetBytesUsed(std::size_t buffer_size) -> std::size_t {
-  assert(stream_.next_frame >= stream_.buffer);
+  if (stream_.next_frame) {
-  return stream_.next_frame - stream_.buffer;
+    std::size_t remaining = stream_.bufend - stream_.next_frame;
+    return buffer_size - remaining;
+  } else {
+    return stream_.bufend - stream_.buffer;
+  }
 }
 
 auto MadMp3Decoder::BeginStream(const cpp::span<const std::byte> input)
@@ -68,13 +73,13 @@ auto MadMp3Decoder::BeginStream(const cpp::span<const std::byte> input)
       continue;
     }
     if (stream_.error == MAD_ERROR_BUFLEN) {
-      return {GetInputPosition(), cpp::fail(Error::kOutOfInput)};
+      return {GetBytesUsed(input.size_bytes()), cpp::fail(Error::kOutOfInput)};
     }
-    return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
+    return {GetBytesUsed(input.size_bytes()), cpp::fail(Error::kMalformedData)};
   }
 
   uint8_t channels = MAD_NCHANNELS(&header);
-  return {GetInputPosition(),
+  return {GetBytesUsed(input.size_bytes()),
           OutputFormat{
               .num_channels = channels,
               .bits_per_sample = 24,  // We always scale to 24 bits
@@ -85,6 +90,7 @@ auto MadMp3Decoder::BeginStream(const cpp::span<const std::byte> input)
 auto MadMp3Decoder::ContinueStream(cpp::span<const std::byte> input,
                                    cpp::span<std::byte> output)
     -> Result<OutputInfo> {
+  std::size_t bytes_read = 0;
   if (current_sample_ < 0) {
     mad_stream_buffer(&stream_,
                       reinterpret_cast<const unsigned char*>(input.data()),
@@ -101,15 +107,18 @@ auto MadMp3Decoder::ContinueStream(cpp::span<const std::byte> input,
       if (stream_.error == MAD_ERROR_BUFLEN) {
         // The decoder ran out of bytes before it completed a frame. We
         // need to return back to the caller to give us more data.
-        return {GetInputPosition(), cpp::fail(Error::kOutOfInput)};
+        return {GetBytesUsed(input.size_bytes()),
+                cpp::fail(Error::kOutOfInput)};
       }
       // The error is unrecoverable. Give up.
-      return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
+      return {GetBytesUsed(input.size_bytes()),
+              cpp::fail(Error::kMalformedData)};
     }
 
     // We've successfully decoded a frame! Now synthesize samples to write out.
     mad_synth_frame(&synth_, &frame_);
     current_sample_ = 0;
+    bytes_read = GetBytesUsed(input.size_bytes());
   }
 
   size_t output_byte = 0;
@@ -117,7 +126,7 @@ auto MadMp3Decoder::ContinueStream(cpp::span<const std::byte> input,
     if (output_byte + (4 * synth_.pcm.channels) >= output.size()) {
       // We can't fit the next sample into the buffer. Stop now, and also avoid
       // writing the sample for only half the channels.
-      return {GetInputPosition(), OutputInfo{.bytes_written = output_byte,
+      return {bytes_read, OutputInfo{.bytes_written = output_byte,
                                      .is_finished_writing = false}};
     }
 
@@ -135,7 +144,7 @@ auto MadMp3Decoder::ContinueStream(cpp::span<const std::byte> input,
 
   // We wrote everything! Reset, ready for the next frame.
   current_sample_ = -1;
-  return {GetInputPosition(), OutputInfo{.bytes_written = output_byte,
+  return {bytes_read, OutputInfo{.bytes_written = output_byte,
                                  .is_finished_writing = true}};
 }
 
@@ -160,7 +169,8 @@ auto MadMp3Decoder::SeekStream(cpp::span<const std::byte> input,
       } else {
         // Don't bother checking for other errors; if the first part of the
         // stream doesn't even contain a header then something's gone wrong.
-        return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
+        return {GetBytesUsed(input.size_bytes()),
+                cpp::fail(Error::kMalformedData)};
       }
     }
 
@@ -184,10 +194,12 @@ auto MadMp3Decoder::SeekStream(cpp::span<const std::byte> input,
         continue;
       }
       if (stream_.error == MAD_ERROR_BUFLEN) {
-        return {GetInputPosition(), cpp::fail(Error::kOutOfInput)};
+        return {GetBytesUsed(input.size_bytes()),
+                cpp::fail(Error::kOutOfInput)};
       }
       // The error is unrecoverable. Give up.
-      return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
+      return {GetBytesUsed(input.size_bytes()),
+              cpp::fail(Error::kMalformedData)};
     }
 
     if (frames_to_go <= 1) {
@@ -202,7 +214,7 @@ auto MadMp3Decoder::SeekStream(cpp::span<const std::byte> input,
       // call.
       current_sample_ =
           (target_sample > current_sample) ? target_sample - current_sample : 0;
-      return {GetInputPosition(), {}};
+      return {GetBytesUsed(input.size_bytes()), {}};
     }
   }
 }