Automatically select best subframe encoding predictor

cmd/wav2flac/main.go

@@ -121,16 +121,6 @@ func wav2flac(wavPath string, force bool) error {
 			//break
 		}
 		for _, subframe := range subframes {
-			subHdr := frame.SubHeader{
-				// Specifies the prediction method used to encode the audio sample of the
-				// subframe.
-				Pred: frame.PredVerbatim,
-				// Prediction order used by fixed and FIR linear prediction decoding.
-				Order: 0,
-				// Wasted bits-per-sample.
-				Wasted: 0,
-			}
-			subframe.SubHeader = subHdr
 			subframe.NSamples = n / nchannels
 			subframe.Samples = subframe.Samples[:subframe.NSamples]
 		}
@@ -138,21 +128,6 @@ func wav2flac(wavPath string, force bool) error {
 			subframe := subframes[i%nchannels]
 			subframe.Samples[i/nchannels] = int32(sample)
 		}
-		// Check if the subframe may be encoded as constant; when all samples are
-		// the same.
-		for _, subframe := range subframes {
-			sample := subframe.Samples[0]
-			constant := true
-			for _, s := range subframe.Samples[1:] {
-				if sample != s {
-					constant = false
-				}
-			}
-			if constant {
-				fmt.Println("constant method")
-				subframe.SubHeader.Pred = frame.PredConstant
-			}
-		}
 
 		// Encode FLAC frame.
 		channels, err := getChannels(nchannels)

encode_subframe.go

@@ -1,6 +1,7 @@
 package flac
 
 import (
+	"bytes"
 	"git.gammaspectra.live/S.O.N.G/flacgo/frame"
 	iobits "git.gammaspectra.live/S.O.N.G/flacgo/internal/bits"
 	"github.com/icza/bitio"
@@ -11,6 +12,25 @@ import (
 
 // encodeSubframe encodes the given subframe, writing to bw.
 func encodeSubframe(bw *bitio.Writer, hdr frame.Header, subframe *frame.Subframe) error {
+	//Select predictor mode
+	predicted := 0
+	subHeader := frame.SubHeader{
+		Pred: frame.PredVerbatim,
+	}
+
+	for i := frame.PredConstant; i < (frame.PredFIR + 1); i++ {
+		shd, estimate := estimateSize(i, hdr, subframe)
+		if estimate > 0 {
+			if predicted == 0 || estimate < predicted {
+				predicted = estimate
+				subHeader = shd
+			}
+		}
+	}
+
+	//Use best
+	subframe.SubHeader = subHeader
+
 	// Encode subframe header.
 	if err := encodeSubframeHeader(bw, subframe.SubHeader); err != nil {
 		return errutil.Err(err)
@@ -23,7 +43,7 @@ func encodeSubframe(bw *bitio.Writer, hdr frame.Header, subframe *frame.Subframe
 			return errutil.Err(err)
 		}
 	case frame.PredVerbatim:
-		if err := encodeVerbatimSamples(bw, hdr, subframe.Samples); err != nil {
+		if err := encodeVerbatimSamples(bw, hdr.BlockSize, hdr.BitsPerSample, subframe.Samples); err != nil {
 			return errutil.Err(err)
 		}
 	//case frame.PredFixed:
@@ -40,6 +60,42 @@ func encodeSubframe(bw *bitio.Writer, hdr frame.Header, subframe *frame.Subframe
 	return nil
 }
 
+func estimateSize(pred frame.Pred, hdr frame.Header, subframe *frame.Subframe) (frame.SubHeader, int) {
+	buf := bytes.NewBuffer([]byte{})
+	bw := bitio.NewWriter(buf)
+
+	switch pred {
+	case frame.PredConstant:
+		if err := encodeConstantSamples(bw, hdr.BitsPerSample, subframe.Samples); err != nil {
+			return frame.SubHeader{}, 0
+		}
+		return frame.SubHeader{
+			Pred:   pred,
+			Order:  0,
+			Wasted: 0,
+		}, buf.Len()
+	case frame.PredVerbatim:
+		if err := encodeVerbatimSamples(bw, hdr.BlockSize, hdr.BitsPerSample, subframe.Samples); err != nil {
+			return frame.SubHeader{}, 0
+		}
+		return frame.SubHeader{
+			Pred:   pred,
+			Order:  0,
+			Wasted: 0,
+		}, buf.Len()
+		//case frame.PredFixed:
+		//	if err := encodeFixedSamples(bw, hdr, subframe.Samples, subframe.Order); err != nil {
+		//		return errutil.Err(err)
+		//	}
+		//case frame.PredFIR:
+		//	if err := encodeFIRSamples(bw, hdr, subframe.Samples, subframe.Order); err != nil {
+		//		return errutil.Err(err)
+		//	}
+
+	}
+	return frame.SubHeader{}, 0
+}
+
 // --- [ Subframe header ] -----------------------------------------------------
 
 // encodeSubframeHeader encodes the given subframe header, writing to bw.
@@ -113,13 +169,13 @@ func encodeConstantSamples(bw *bitio.Writer, bps byte, samples []int32) error {
 
 // encodeVerbatimSamples stores the given samples verbatim (uncompressed),
 // writing to bw.
-func encodeVerbatimSamples(bw *bitio.Writer, hdr frame.Header, samples []int32) error {
+func encodeVerbatimSamples(bw *bitio.Writer, blockSize uint16, bps byte, samples []int32) error {
 	// Unencoded subblock; n = frame's bits-per-sample, i = frame's blocksize.
-	if int(hdr.BlockSize) != len(samples) {
-		return errutil.Newf("block size and sample count mismatch; expected %d, got %d", hdr.BlockSize, len(samples))
+	if int(blockSize) != len(samples) {
+		return errutil.Newf("block size and sample count mismatch; expected %d, got %d", blockSize, len(samples))
 	}
 	for _, sample := range samples {
-		if err := bw.WriteBits(uint64(sample), hdr.BitsPerSample); err != nil {
+		if err := bw.WriteBits(uint64(sample), bps); err != nil {
 			return errutil.Err(err)
 		}
 	}