LibAudio: Make Loader::seek() treat its input as a sample index

This fixes a bug where if you try to play a Wave file a second
time (or loop with `aplay -l`), the second time will be pure
noise.

The function `Audio::Loader::seek` is meant to seek to a specific
audio sample, e.g. seek(0) should go to the first audio sample.
However, WavLoader was interpreting seek(0) as the beginning
of the file or stream, which contains non-audio header data.

This fixes the bug by capturing the byte offset of the start of the
audio data, and offseting the raw file/stream seek by that amount.

Userland/Libraries/LibAudio/Loader.h

@@ -27,7 +27,8 @@ public:
     virtual RefPtr<Buffer> get_more_samples(size_t max_bytes_to_read_from_input = 128 * KiB) = 0;
 
     virtual void reset() = 0;
-    virtual void seek(const int position) = 0;
+
+    virtual void seek(const int sample_index) = 0;
 
     virtual int loaded_samples() = 0;
     virtual int total_samples() = 0;

Userland/Libraries/LibAudio/WavLoader.cpp

@@ -83,13 +83,14 @@ RefPtr<Buffer> WavLoaderPlugin::get_more_samples(size_t max_bytes_to_read_from_i
     return buffer;
 }
 
-void WavLoaderPlugin::seek(const int position)
+void WavLoaderPlugin::seek(const int sample_index)
 {
-    if (position < 0 || position > m_total_samples)
+    dbgln_if(AWAVLOADER_DEBUG, "seek sample_index {}", sample_index);
+    if (sample_index < 0 || sample_index >= m_total_samples)
         return;
 
-    m_loaded_samples = position;
-    size_t byte_position = position * m_num_channels * (pcm_bits_per_sample(m_sample_format) / 8);
+    m_loaded_samples = sample_index;
+    size_t byte_position = m_byte_offset_of_data_samples + sample_index * m_num_channels * (pcm_bits_per_sample(m_sample_format) / 8);
 
     // AK::InputStream does not define seek.
     if (m_file) {
@@ -105,12 +106,14 @@ bool WavLoaderPlugin::parse_header()
         return false;
 
     bool ok = true;
+    size_t bytes_read = 0;
 
     auto read_u8 = [&]() -> u8 {
         u8 value;
         *m_stream >> value;
         if (m_stream->handle_any_error())
             ok = false;
+        bytes_read += 1;
         return value;
     };
 
@@ -119,6 +122,7 @@ bool WavLoaderPlugin::parse_header()
         *m_stream >> value;
         if (m_stream->handle_any_error())
             ok = false;
+        bytes_read += 2;
         return value;
     };
 
@@ -127,6 +131,7 @@ bool WavLoaderPlugin::parse_header()
         *m_stream >> value;
         if (m_stream->handle_any_error())
             ok = false;
+        bytes_read += 4;
         return value;
     };
 
@@ -245,6 +250,7 @@ bool WavLoaderPlugin::parse_header()
         bytes_per_sample,
         m_total_samples);
 
+    m_byte_offset_of_data_samples = bytes_read;
     return true;
 }
 

Userland/Libraries/LibAudio/WavLoader.h

@@ -44,7 +44,10 @@ public:
     virtual RefPtr<Buffer> get_more_samples(size_t max_bytes_to_read_from_input = 128 * KiB) override;
 
     virtual void reset() override { return seek(0); }
-    virtual void seek(const int position) override;
+
+    // sample_index 0 is the start of the raw audio sample data
+    // within the file/stream.
+    virtual void seek(const int sample_index) override;
 
     virtual int loaded_samples() override { return m_loaded_samples; }
     virtual int total_samples() override { return m_total_samples; }
@@ -66,6 +69,7 @@ private:
     u32 m_sample_rate { 0 };
     u16 m_num_channels { 0 };
     PcmSampleFormat m_sample_format;
+    size_t m_byte_offset_of_data_samples { 0 };
 
     int m_loaded_samples { 0 };
     int m_total_samples { 0 };