aubuf: prevent faulty timestamps (#75)

* aubuf: prevent faulty timestamps for partial read

There are applications where a useful timestamp is not available. E.g. if audio
files are read and decoded. Then audio frames are written to aubuf with
`timestamp == 0`. In such cases a partial read with `aubuf_read_auframe()` set
a wrong timestamp to the rest frame.

* aubuf: set correct timestamps if app provides zero

For partial read timestamps are changed for the rest frames. This works only
if the timestamps are already set correctly during writing.

This commit handles also the case correct if the application provides
timestamps and the first frame has timestamp zero and the first read is
partial.

* aubuf,auframe: move auframe_bytes_to_timestamp() to auframe

* aubuf: reset also written_sz in aubuf_flush()

include/rem_auframe.h

@@ -2,6 +2,8 @@
  * Audio frame
  */
 
+#define AUDIO_TIMEBASE 1000000U
+
 /**
  * Defines a frame of audio samples
  */
@@ -42,3 +44,4 @@ static inline void auframe_update(struct auframe *af, void *sampv,
 size_t auframe_size(const struct auframe *af);
 void   auframe_mute(struct auframe *af);
 double auframe_level(struct auframe *af);
+size_t auframe_bytes_to_timestamp(const struct auframe *af, size_t n);

src/aubuf/ajb.h

@@ -4,8 +4,6 @@
  * Copyright (C) 2022 Commend.com - c.spielberger@commend.com
  */
 
-#define AUDIO_TIMEBASE 1000000U
-
 enum ajb_state {
 	AJB_GOOD = 0,
 	AJB_LOW,

src/aubuf/aubuf.c

@@ -24,6 +24,7 @@ struct aubuf {
 	size_t max_sz;
 	size_t fill_sz;         /**< To fill size                            */
 	size_t pkt_sz;          /**< Packet size                             */
+	size_t wr_sz;           /**< Written size                            */
 	bool started;
 	uint64_t ts;
 
@@ -91,8 +92,9 @@ static void read_auframe(struct aubuf *ab, struct auframe *af)
 			mem_deref(f);
 		}
 		else if (af->srate && af->ch && sample_size) {
-			f->af.timestamp += n * AUDIO_TIMEBASE /
-				(af->srate * af->ch * sample_size);
+
+			f->af.timestamp +=
+				auframe_bytes_to_timestamp(&f->af, n);
 		}
 
 		if (n == sz)
@@ -235,8 +237,14 @@ int aubuf_append_auframe(struct aubuf *ab, struct mbuf *mb,
 	if (ab->fill_sz >= ab->pkt_sz)
 		ab->fill_sz -= ab->pkt_sz;
 
+	if (!f->af.timestamp && f->af.srate && f->af.ch) {
+		f->af.timestamp =
+			auframe_bytes_to_timestamp(&f->af, ab->wr_sz);
+	}
+
 	list_insert_sorted(&ab->afl, frame_less_equal, NULL, &f->le, f);
 	ab->cur_sz += sz;
+	ab->wr_sz += sz;
 
 	if (ab->max_sz && ab->cur_sz > ab->max_sz) {
 #if AUBUF_DEBUG
@@ -446,6 +454,7 @@ void aubuf_flush(struct aubuf *ab)
 	list_flush(&ab->afl);
 	ab->fill_sz = ab->wish_sz;
 	ab->cur_sz  = 0;
+	ab->wr_sz   = 0;
 	ab->ts      = 0;
 
 	mtx_unlock(ab->lock);

src/auframe/auframe.c

@@ -101,3 +101,11 @@ double auframe_level(struct auframe *af)
 
 	return af->level;
 }
+
+
+size_t auframe_bytes_to_timestamp(const struct auframe *af, size_t n)
+{
+	size_t sample_size = aufmt_sample_size(af->fmt);
+
+	return n * AUDIO_TIMEBASE / (af->srate * af->ch * sample_size);
+}