dsoundaudio: fix crackling audio recordings

Audio recordings with the DirectSound backend don't sound right.
A look a the Microsoft online documentation tells us why.

From the DirectSound Programming Guide, Capture Buffer Information:
'You can safely copy data from the buffer only up to the read
cursor.'

Change the code to read up to the read cursor instead of the
capture cursor.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20211226154017.6067-2-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/audio/dsoundaudio.c b/audio/dsoundaudio.c
index cfc79c129e..3dd2c4d4a6 100644
--- a/audio/dsoundaudio.c
+++ b/audio/dsoundaudio.c
@@ -536,13 +536,12 @@ static void *dsound_get_buffer_in(HWVoiceIn *hw, size_t *size)
     DSoundVoiceIn *ds = (DSoundVoiceIn *) hw;
     LPDIRECTSOUNDCAPTUREBUFFER dscb = ds->dsound_capture_buffer;
     HRESULT hr;
-    DWORD cpos, rpos, act_size;
+    DWORD rpos, act_size;
     size_t req_size;
     int err;
     void *ret;
 
-    hr = IDirectSoundCaptureBuffer_GetCurrentPosition(
-        dscb, &cpos, ds->first_time ? &rpos : NULL);
+    hr = IDirectSoundCaptureBuffer_GetCurrentPosition(dscb, NULL, &rpos);
     if (FAILED(hr)) {
         dsound_logerr(hr, "Could not get capture buffer position\n");
         *size = 0;
@@ -554,7 +553,7 @@ static void *dsound_get_buffer_in(HWVoiceIn *hw, size_t *size)
         ds->first_time = false;
     }
 
-    req_size = audio_ring_dist(cpos, hw->pos_emul, hw->size_emul);
+    req_size = audio_ring_dist(rpos, hw->pos_emul, hw->size_emul);
     req_size = MIN(*size, MIN(req_size, hw->size_emul - hw->pos_emul));
 
     if (req_size == 0) {