MT#56471 mix_buffer: support initial write-delay

This is to compensate for inter-packet arrival jitter.

Change-Id: I5cdfb4bbda8e90b82f5abe410f48329070d7005b

lib/mix_buffer.c

@@ -189,11 +189,31 @@ static bool mix_buffer_write_slow(struct mix_buffer *mb, struct mix_buffer_ssrc_
 }
 
 
+static void mix_buffer_src_add_delay(struct mix_buffer *mb, struct mix_buffer_ssrc_source *src,
+		unsigned int samples)
+{
+	if (!samples)
+		return;
+	// shift new write pos into the future
+	src->write_pos += samples;
+	if (src->write_pos >= mb->size) {
+		src->write_pos -= mb->size;
+		src->loops++;
+	}
+	// fill up buffer if needed
+	if (src->loops == mb->loops && src->write_pos > mb->head_write_pos)
+		fill_up_to(mb, mb->fill + src->write_pos - mb->head_write_pos);
+	else if (src->loops == mb->loops + 1 && src->write_pos < mb->head_write_pos)
+		fill_up_to(mb, mb->fill + src->write_pos + mb->size - mb->head_write_pos);
+}
+
+
 static void mix_buffer_src_init_pos(struct mix_buffer *mb, struct mix_buffer_ssrc_source *src) {
 	src->write_pos = mb->read_pos;
 	src->loops = mb->loops;
 	if (mb->head_write_pos < src->write_pos)
 		src->loops--;
+	mix_buffer_src_add_delay(mb, src, mb->delay);
 }
 
 
@@ -230,7 +250,6 @@ bool mix_buffer_write(struct mix_buffer *mb, uint32_t ssrc, const void *buf, uns
 
 		// we fell behind. reset write position to current read pos and try again
 		mix_buffer_src_init_pos(mb, src);
-		// TODO: add offset to correct for jitter/delay
 	}
 }
 
@@ -245,7 +264,7 @@ static struct ssrc_entry *mix_buffer_ssrc_new(void *p) {
 
 // struct must be zeroed already
 bool mix_buffer_init(struct mix_buffer *mb, enum AVSampleFormat fmt, unsigned int clockrate,
-		unsigned int channels, unsigned int size_ms)
+		unsigned int channels, unsigned int size_ms, unsigned int delay_ms)
 {
 	switch (fmt) {
 		case AV_SAMPLE_FMT_S16:
@@ -256,6 +275,7 @@ bool mix_buffer_init(struct mix_buffer *mb, enum AVSampleFormat fmt, unsigned in
 	}
 
 	unsigned int size = clockrate * size_ms / 1000; // in samples
+	unsigned int delay = clockrate * delay_ms / 1000; // in samples
 
 	mutex_init(&mb->lock);
 	mb->sample_size_channels = channels * mb->impl->sample_size;
@@ -263,8 +283,9 @@ bool mix_buffer_init(struct mix_buffer *mb, enum AVSampleFormat fmt, unsigned in
 	mb->size = size;
 	mb->clockrate = clockrate;
 	mb->channels = channels;
+	mb->delay = delay;
 
-	mb->ssrc_hash = create_ssrc_hash_full(mix_buffer_ssrc_new, mb);
+	mb->ssrc_hash = create_ssrc_hash_full_fast(mix_buffer_ssrc_new, mb);
 
 	return true;
 }

lib/mix_buffer.h

@@ -47,6 +47,8 @@ struct mix_buffer {
 	unsigned int read_pos; // current read (output) position
 	unsigned int head_write_pos; // furthest ahead write (input) position
 	unsigned int fill; // difference between read and write position
+	unsigned int delay; // initial write delay for new inputs/sources
+
 	unsigned int loops; // how many times the write pos has circled around
 
 	// implementation details
@@ -57,7 +59,7 @@ struct mix_buffer {
 
 
 bool mix_buffer_init(struct mix_buffer *, enum AVSampleFormat, unsigned int clockrate,
-		unsigned int channels, unsigned int size_ms);
+		unsigned int channels, unsigned int size_ms, unsigned int delay_ms);
 void mix_buffer_destroy(struct mix_buffer *);
 
 void *mix_buffer_read_fast(struct mix_buffer *, unsigned int samples, unsigned int *size);

t/test-mix-buffer.c

@@ -24,7 +24,7 @@ int main(void) {
 	struct mix_buffer mb;
 
 	memset(&mb, 0, sizeof(mb));
-	bool ret = mix_buffer_init(&mb, AV_SAMPLE_FMT_S16, 500, 1, 100);
+	bool ret = mix_buffer_init(&mb, AV_SAMPLE_FMT_S16, 500, 1, 100, 0);
 	assert(ret == true);
 
 	// pre-fill with zeroes
@@ -235,7 +235,7 @@ int main(void) {
 	// 2-channel
 
 	memset(&mb, 0, sizeof(mb));
-	ret = mix_buffer_init(&mb, AV_SAMPLE_FMT_S16, 500, 2, 100);
+	ret = mix_buffer_init(&mb, AV_SAMPLE_FMT_S16, 500, 2, 100, 0);
 	assert(ret == true);
 
 	// pre-fill with zeroes
@@ -417,5 +417,41 @@ int main(void) {
 
 	mix_buffer_destroy(&mb);
 
+
+
+	// initial delay
+
+	memset(&mb, 0, sizeof(mb));
+	ret = mix_buffer_init(&mb, AV_SAMPLE_FMT_S16, 500, 1, 100, 10); // 5 samples delay
+	assert(ret == true);
+
+	// write-in and read-out
+
+	ret = mix_buffer_write(&mb, 0x1234, "1122334455", 5);
+	assert(ret == true);
+
+	p = mix_buffer_read_fast(&mb, 15, &size);
+	assert(p != NULL);
+	assert(size == 30);
+	assert(memcmp(p, "\0\0\0\0\0\0\0\0\0\0" "1122334455" "\0\0\0\0\0\0\0\0\0\0", size) == 0);
+
+	ret = mix_buffer_write(&mb, 0x1234, "1122334455", 5);
+	assert(ret == true);
+
+	p = mix_buffer_read_fast(&mb, 10, &size);
+	assert(p != NULL);
+	assert(size == 20);
+	assert(memcmp(p, "\0\0\0\0\0\0\0\0\0\0" "1122334455", size) == 0);
+
+	ret = mix_buffer_write(&mb, 0x1234, "1122334455", 5);
+	assert(ret == true);
+
+	p = mix_buffer_read_fast(&mb, 10, &size);
+	assert(p != NULL);
+	assert(size == 20);
+	assert(memcmp(p, "1122334455" "\0\0\0\0\0\0\0\0\0\0", size) == 0);
+
+	mix_buffer_destroy(&mb);
+
 	return 0;
 }