start work on the smpl metadata codec

smpl_chunk.go

@@ -0,0 +1,69 @@
+package wav
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+
+	"github.com/mattetti/audio/riff"
+)
+
+// smpl chunk is documented here:
+// https://sites.google.com/site/musicgapi/technical-documents/wav-file-format#smpl
+
+// DecodeSamplerChunk decodes a smpl chunk and put the data in Decoder.Metadata.SamplerInfo
+func DecodeSamplerChunk(d *Decoder, ch *riff.Chunk) error {
+	if ch == nil {
+		return fmt.Errorf("can't decode a nil chunk")
+	}
+	if d == nil {
+		return fmt.Errorf("nil decoder")
+	}
+	if ch.ID == CIDSmpl {
+		// read the entire chunk in memory
+		buf := make([]byte, ch.Size)
+		var err error
+		if _, err = ch.Read(buf); err != nil {
+			return fmt.Errorf("failed to read the smpl chunk - %v", err)
+		}
+		if d.Metadata == nil {
+			d.Metadata = &Metadata{}
+		}
+
+		d.Metadata.SamplerInfo = &SamplerInfo{}
+
+		r := bytes.NewReader(buf)
+
+		scratch := make([]byte, 4)
+		if _, err = r.Read(scratch); err != nil {
+			return fmt.Errorf("failed to read the smpl Manufacturer")
+		}
+		copy(d.Metadata.SamplerInfo.Manufacturer[:], scratch[:4])
+		if _, err = r.Read(scratch); err != nil {
+			return fmt.Errorf("failed to read the smpl Product")
+		}
+		copy(d.Metadata.SamplerInfo.Product[:], scratch[:4])
+
+		if err := binary.Read(r, binary.BigEndian, &d.Metadata.SamplerInfo.SamplePeriod); err != nil {
+			return err
+		}
+		if err := binary.Read(r, binary.BigEndian, &d.Metadata.SamplerInfo.MIDIUnityNote); err != nil {
+			return err
+		}
+		if err := binary.Read(r, binary.BigEndian, &d.Metadata.SamplerInfo.MIDIPitchFraction); err != nil {
+			return err
+		}
+		if err := binary.Read(r, binary.BigEndian, &d.Metadata.SamplerInfo.SMPTEFormat); err != nil {
+			return err
+		}
+		if err := binary.Read(r, binary.BigEndian, &d.Metadata.SamplerInfo.SMPTEOffset); err != nil {
+			return err
+		}
+		if err := binary.Read(r, binary.BigEndian, &d.Metadata.SamplerInfo.NumSampleLoops); err != nil {
+			return err
+		}
+		//TODO: loops
+	}
+	ch.Drain()
+	return nil
+}