New version 0.1.0 which fixes decoding delay

New API function aptx_encode_finish() flushes encoding buffer and adds last
90 encoded samples, so caller has ability to encode whole input stream.

Function aptx_decode() was fixed to drop first 90 decoded samples which are
used just for predictor and contain noise.

Author: pali

Makefile

@@ -1,5 +1,5 @@
 MAJOR := 0
-MINOR := 0
+MINOR := 1
 PATCH := 0
 
 PREFIX := /usr/local
@@ -11,9 +11,10 @@ LIBNAME := libopenaptx.so
 SONAME := $(LIBNAME).$(MAJOR)
 FILENAME := $(SONAME).$(MINOR).$(PATCH)
 
-UTILITIES := openaptxenc openaptxdec
+UTILITIES := openaptxenc openaptxdec openaptxenc-static openaptxdec-static
 
 HEADERS := openaptx.h
+SOURCES := openaptx.c
 
 BUILD := $(FILENAME) $(SONAME) $(LIBNAME) $(UTILITIES)
 
@@ -27,15 +28,18 @@ install: $(BUILD)
 	mkdir -p $(DESTDIR)/$(PREFIX)/$(INCDIR)
 	cp -a $(HEADERS) $(DESTDIR)/$(PREFIX)/$(INCDIR)
 
-$(FILENAME): openaptx.c $(HEADERS)
-	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -I. -shared -fPIC -Wl,-soname,$(SONAME) -o $@ $<
+$(FILENAME): $(SOURCES) $(HEADERS)
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -I. -shared -fPIC -Wl,-soname,$(SONAME) -o $@ $(SOURCES)
 
 $(SONAME): $(FILENAME)
 	ln -sf $< $@
 
 $(LIBNAME): $(SONAME)
 	ln -sf $< $@
 
+%-static: %.c $(SOURCES) $(HEADERS)
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -I. -o $@ $< $(SOURCES)
+
 %: %.c $(LIBNAME) $(HEADERS)
 	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -I. -o $@ $< $(LIBNAME)
 

openaptx.c

@@ -78,9 +78,10 @@ enum subbands {
 
 #define NB_FILTERS 2
 #define FILTER_TAPS 16
+#define LATENCY_SAMPLES 90
 
 struct aptx_filter_signal {
-    int pos;
+    uint8_t pos;
     int32_t buffer[2*FILTER_TAPS];
 };
 
@@ -124,8 +125,10 @@ struct aptx_channel {
 } ;
 
 struct aptx_context {
-    int hd;
-    int32_t sync_idx;
+    uint8_t hd;
+    uint8_t sync_idx;
+    uint8_t encode_remaining;
+    uint8_t decode_skip_leading;
     struct aptx_channel channels[NB_CHANNELS];
 };
 
@@ -900,20 +903,19 @@ static int32_t aptx_quantized_parity(struct aptx_channel *channel)
 
 /* For each sample, ensure that the parity of all subbands of all channels
  * is 0 except once every 8 samples where the parity is forced to 1. */
-static int aptx_check_parity(struct aptx_channel channels[NB_CHANNELS], int32_t *idx)
+static int aptx_check_parity(struct aptx_channel channels[NB_CHANNELS], uint8_t *sync_idx)
 {
     int32_t parity = aptx_quantized_parity(&channels[LEFT])
                    ^ aptx_quantized_parity(&channels[RIGHT]);
+    int32_t eighth = *sync_idx == 7;
 
-    int eighth = *idx == 7;
-    *idx = (*idx + 1) & 7;
-
+    *sync_idx = (*sync_idx + 1) & 7;
     return parity ^ eighth;
 }
 
-static void aptx_insert_sync(struct aptx_channel channels[NB_CHANNELS], int32_t *idx)
+static void aptx_insert_sync(struct aptx_channel channels[NB_CHANNELS], uint8_t *sync_idx)
 {
-    if (aptx_check_parity(channels, idx)) {
+    if (aptx_check_parity(channels, sync_idx)) {
         int i;
         struct aptx_channel *c;
         static const int map[] = { 1, 2, 0, 3 };
@@ -1022,6 +1024,10 @@ static int aptx_decode_samples(struct aptx_context *ctx,
 }
 
 
+int aptx_major = OPENAPTX_MAJOR;
+int aptx_minor = OPENAPTX_MINOR;
+int aptx_patch = OPENAPTX_PATCH;
+
 struct aptx_context *aptx_init(int hd)
 {
     struct aptx_context *ctx;
@@ -1043,6 +1049,8 @@ void aptx_reset(struct aptx_context *ctx)
     hd = ctx->hd;
     memset(ctx, 0, sizeof(*ctx));
     ctx->hd = hd;
+    ctx->decode_skip_leading = (LATENCY_SAMPLES+3)/4;
+    ctx->encode_remaining = (LATENCY_SAMPLES+3)/4;
 
     for (chan = 0; chan < NB_CHANNELS; chan++) {
         struct aptx_channel *channel = &ctx->channels[chan];
@@ -1071,7 +1079,7 @@ size_t aptx_encode(struct aptx_context *ctx, const unsigned char *input, size_t
     for (ipos = 0, opos = 0; ipos + 3*NB_CHANNELS*4 <= input_size && opos + sample_size <= output_size; opos += sample_size) {
         for (sample = 0; sample < 4; sample++) {
             for (channel = 0; channel < NB_CHANNELS; channel++, ipos += 3) {
-                /* samples need to contain 24bit signed intger stored as 32bit signed integers */
+                /* samples need to contain 24bit signed integer stored as 32bit signed integers */
                 /* last int8_t --> uint32_t cast propagates sign bit for 32bit integer */
                 samples[channel][sample] = ((uint32_t)input[ipos+0] << 0) |
                                            ((uint32_t)input[ipos+1] << 8) |
@@ -1085,6 +1093,31 @@ size_t aptx_encode(struct aptx_context *ctx, const unsigned char *input, size_t
     return ipos;
 }
 
+int aptx_encode_finish(struct aptx_context *ctx, unsigned char *output, size_t output_size, size_t *written)
+{
+    const int32_t samples[NB_CHANNELS][4] = { };
+    int sample_size;
+    size_t opos;
+
+    sample_size = ctx->hd ? 6 : 4;
+
+    if (ctx->encode_remaining == 0) {
+        *written = 0;
+        return 1;
+    }
+
+    for (opos = 0; ctx->encode_remaining > 0 && opos + sample_size <= output_size; ctx->encode_remaining--, opos += sample_size)
+        aptx_encode_samples(ctx, samples, output + opos);
+
+    *written = opos;
+
+    if (ctx->encode_remaining > 0)
+        return 0;
+
+    aptx_reset(ctx);
+    return 1;
+}
+
 size_t aptx_decode(struct aptx_context *ctx, const unsigned char *input, size_t input_size, unsigned char *output, size_t output_size, size_t *written)
 {
     int32_t samples[NB_CHANNELS][4];
@@ -1097,7 +1130,14 @@ size_t aptx_decode(struct aptx_context *ctx, const unsigned char *input, size_t
     for (ipos = 0, opos = 0; ipos + sample_size <= input_size && opos + 3*NB_CHANNELS*4 <= output_size; ipos += sample_size) {
         if (aptx_decode_samples(ctx, input + ipos, samples))
             break;
-        for (sample = 0; sample < 4; sample++) {
+        sample = 0;
+        if (ctx->decode_skip_leading > 0) {
+            ctx->decode_skip_leading--;
+            if (ctx->decode_skip_leading > 0)
+                continue;
+            sample = LATENCY_SAMPLES%4;
+        }
+        for (; sample < 4; sample++) {
             for (channel = 0; channel < NB_CHANNELS; channel++, opos += 3) {
                 /* samples contain 24bit signed integers stored as 32bit signed integers */
                 /* we do not need to care about negative integers specially as they have 24. bit set */

openaptx.h

@@ -21,9 +21,15 @@
 #define OPENAPTX_H
 
 #define OPENAPTX_MAJOR 0
-#define OPENAPTX_MINOR 0
+#define OPENAPTX_MINOR 1
 #define OPENAPTX_PATCH 0
 
+#include <stddef.h>
+
+extern int aptx_major;
+extern int aptx_minor;
+extern int aptx_patch;
+
 struct aptx_context;
 
 /*
@@ -62,6 +68,20 @@ size_t aptx_encode(struct aptx_context *ctx,
                    size_t output_len,
                    size_t *written);
 
+/*
+ * Finish encoding of current stream and reset internal state to be ready for
+ * encoding new stream. Due to aptX latency, last 90 samples (rounded to 92)
+ * will be filled by this finish function. When output buffer is too small, this
+ * function returns zero, fills buffer only partially, does not reset internal
+ * state and subsequent calls continue filling output buffer. When output buffer
+ * is large enough, then function returns non-zero value. In both cases into
+ * written pointer is stored length of encoded samples.
+ */
+int aptx_encode_finish(struct aptx_context *ctx,
+                       unsigned char *output,
+                       size_t output_len,
+                       size_t *written);
+
 /*
  * Decodes aptX audio samples in input buffer with size input_len to sequence
  * of raw 24bit signed stereo samples into output buffer with size output_len.
@@ -72,7 +92,8 @@ size_t aptx_encode(struct aptx_context *ctx,
  * sequence of 24 bytes in format LLLRRRLLLRRRLLLRRRLLLRRR (L-left, R-right)
  * for one aptX sample. Due to aptX parity check it is suggested to provide
  * multiple of eight aptX samples, therefore multiple of 8*4 bytes for aptX
- * reps. 8*6 bytes for aptX HD.
+ * and 8*6 bytes for aptX HD. Due to aptX latency, output buffer starts filling
+ * after 90 samples.
  */
 size_t aptx_decode(struct aptx_context *ctx,
                    const unsigned char *input,

openaptxdec.c

@@ -42,7 +42,7 @@ int main(int argc, char *argv[])
 
     for (i = 1; i < argc; ++i) {
         if (strcmp(argv[i], "-h") == 0 || strcmp(argv[i], "--help") == 0) {
-            fprintf(stderr, "aptX decoder utility\n");
+            fprintf(stderr, "aptX decoder utility %d.%d.%d (using libopenaptx %d.%d.%d)\n", OPENAPTX_MAJOR, OPENAPTX_MINOR, OPENAPTX_PATCH, aptx_major, aptx_minor, aptx_patch);
             fprintf(stderr, "\n");
             fprintf(stderr, "This utility decodes aptX or aptX HD audio stream\n");
             fprintf(stderr, "from stdin to a raw 24 bit signed stereo on stdout\n");
@@ -86,12 +86,12 @@ int main(int argc, char *argv[])
     length = fread(input_buffer, 1, 6, stdin);
     if (length >= 4 && memcmp(input_buffer, "\x4b\xbf\x4b\xbf", 4) == 0) {
         if (hd)
-            fprintf(stderr, "%s: Input looks like aptX audio stream (not aptX HD), try without --hd\n", argv[0]);
+            fprintf(stderr, "%s: Input looks like start of aptX audio stream (not aptX HD), try without --hd\n", argv[0]);
     } else if (length >= 6 && memcmp(input_buffer, "\x73\xbe\xff\x73\xbe\xff", 6) == 0) {
         if (!hd)
-            fprintf(stderr, "%s: Input looks like aptX HD audio stream, try with --hd\n", argv[0]);
+            fprintf(stderr, "%s: Input looks like start of aptX HD audio stream, try with --hd\n", argv[0]);
     } else {
-        fprintf(stderr, "%s: Input does not look like aptX nor aptX HD audio stream\n", argv[0]);
+        fprintf(stderr, "%s: Input does not look like start of aptX nor aptX HD audio stream, trying to synchronize\n", argv[0]);
     }
 
     while (length > 0 || !feof(stdin)) {
@@ -140,8 +140,6 @@ int main(int argc, char *argv[])
                 processed = 1;
                 written = 0;
             }
-        } else if (length < sample_size) {
-            fprintf(stderr, "%s: aptX decoding stopped in the middle of the sample\n", argv[0]);
         }
 
         if (written > 0) {

openaptxenc.c

@@ -38,7 +38,7 @@ int main(int argc, char *argv[])
 
     for (i = 1; i < argc; ++i) {
         if (strcmp(argv[i], "-h") == 0 || strcmp(argv[i], "--help") == 0) {
-            fprintf(stderr, "aptX encoder utility\n");
+            fprintf(stderr, "aptX encoder utility %d.%d.%d (using libopenaptx %d.%d.%d)\n", OPENAPTX_MAJOR, OPENAPTX_MINOR, OPENAPTX_PATCH, aptx_major, aptx_minor, aptx_patch);
             fprintf(stderr, "\n");
             fprintf(stderr, "This utility encodes a raw 24 bit signed stereo\n");
             fprintf(stderr, "samples from stdin to aptX or aptX HD on stdout\n");
@@ -78,8 +78,6 @@ int main(int argc, char *argv[])
         processed = aptx_encode(ctx, input_buffer, length, output_buffer, sizeof(output_buffer), &written);
         if (processed != length)
             fprintf(stderr, "%s: aptX encoding stopped in the middle of the sample, dropped %u bytes\n", argv[0], (unsigned int)(length-processed));
-        else if (processed % (8*3*2*4))
-            fprintf(stderr, "%s: aptX encoding stopped in the middle of the sample\n", argv[0]);
         if (fwrite(output_buffer, 1, written, stdout) != written) {
             fprintf(stderr, "%s: aptX encoding failed to write encoded data\n", argv[0]);
             break;
@@ -88,6 +86,11 @@ int main(int argc, char *argv[])
             break;
     }
 
+    if (aptx_encode_finish(ctx, output_buffer, sizeof(output_buffer), &written)) {
+        if (fwrite(output_buffer, 1, written, stdout) != written)
+            fprintf(stderr, "%s: aptX encoding failed to write encoded data\n", argv[0]);
+    }
+
     aptx_finish(ctx);
     return 0;
 }