basesrc: fix startup position in the ringbuffer

When we start and we need to produce the first sample, go to the next sample
that will be written into the ringbuffer instead of trying to go to sample 0.
We relied on rather small ringbuffer sizes to correctly go to the current
sample, which breaks whith large buffers.

Fixes #600945

diff --git a/gst-libs/gst/audio/gstbaseaudiosrc.c b/gst-libs/gst/audio/gstbaseaudiosrc.c
index abf07ca..8ec3b7d 100644 (file)
--- a/gst-libs/gst/audio/gstbaseaudiosrc.c
+++ b/gst-libs/gst/audio/gstbaseaudiosrc.c
@@ -699,33 +699,39 @@ gst_base_audio_src_get_offset (GstBaseAudioSrc * src)
 
   /* assume we can append to the previous sample */
   sample = src->next_sample;
-  /* no previous sample, try to read from position 0 */
-  if (sample == -1)
-    sample = 0;
 
   sps = src->ringbuffer->samples_per_seg;
   segtotal = src->ringbuffer->spec.segtotal;
 
-  /* figure out the segment and the offset inside the segment where
-   * the sample should be read from. */
-  readseg = sample / sps;
-
   /* get the currently processed segment */
   segdone = g_atomic_int_get (&src->ringbuffer->segdone)
       - src->ringbuffer->segbase;
 
-  GST_DEBUG_OBJECT (src, "reading from %d, we are at %d", readseg, segdone);
-
-  /* see how far away it is from the read segment, normally segdone (where new
-   * data is written in the ringbuffer) is bigger than readseg (where we are
-   * reading). */
-  diff = segdone - readseg;
-  if (diff >= segtotal) {
-    GST_DEBUG_OBJECT (src, "dropped, align to segment %d", segdone);
-    /* sample would be dropped, position to next playable position */
+  if (sample != -1) {
+    GST_DEBUG_OBJECT (src, "at sample %" G_GUINT64_FORMAT, segdone, sample);
+    /* figure out the segment and the offset inside the segment where
+     * the sample should be read from. */
+    readseg = sample / sps;
+
+    /* see how far away it is from the read segment, normally segdone (where new
+     * data is written in the ringbuffer) is bigger than readseg (where we are
+     * reading). */
+    diff = segdone - readseg;
+    if (diff >= segtotal) {
+      GST_DEBUG_OBJECT (src, "dropped, align to segment %d", segdone);
+      /* sample would be dropped, position to next playable position */
+      sample = ((guint64) (segdone)) * sps;
+    }
+  } else {
+    /* no previous sample, go to the current position */
+    GST_DEBUG_OBJECT (src, "first sample, align to current %d", segdone);
     sample = ((guint64) (segdone)) * sps;
   }
 
+  GST_DEBUG_OBJECT (src,
+      "reading from %d, we are at %d, sample %" G_GUINT64_FORMAT, readseg,
+      segdone, sample);
+
   return sample;
 }