talk/voice: Reduce the size of the commit buffer.

The voice engine can now request more voice data during decoding, it does
not require the entire clip to be available before start of decoding anymore.
Therefore the commit buffer does not need to hold an entire voice clip anymore,
and can be made greatly smaller.

Change-Id: I3eca9026448e725b9b8d0dae1efca0ad185371da

1 files changed, 25 insertions, 0 deletions

diff --git a/apps/voice_thread.c b/apps/voice_thread.c
index 72ecb3741e..dcb7eef224 100644
--- a/apps/voice_thread.c
+++ b/apps/voice_thread.c
@@ -63,9 +63,17 @@
    latency */
 #define PRIORITY_VOICE (PRIORITY_PLAYBACK-4)
 
+/* A speex frame generally consists of 20ms of audio
+ * (http://www.speex.org/docs/manual/speex-manual/node10.html)
+ * for wideband mode this results in 320 samples of decoded PCM.
+ */
 #define VOICE_FRAME_COUNT   320 /* Samples / frame */
 #define VOICE_SAMPLE_RATE 16000 /* Sample rate in HZ */
 #define VOICE_SAMPLE_DEPTH   16 /* Sample depth in bits */
+/* The max. wideband bitrate is 42.4 kbps
+ * (http://www.speex.org/docs/manual/speex-manual/node11.html). For 20ms
+ * this gives a maximum of 106 bytes for an encoded speex frame */
+#define VOICE_MAX_ENCODED_FRAME_SIZE 106
 
 /* Voice thread variables */
 static unsigned int voice_thread_id = 0;
@@ -449,6 +457,23 @@ static enum voice_state voice_decode(struct voice_thread_data *td)
     }
     else
     {
+        if (td->vi.size > VOICE_MAX_ENCODED_FRAME_SIZE
+            && td->bits.charPtr > (td->vi.size - VOICE_MAX_ENCODED_FRAME_SIZE)
+            && td->vi.get_more != NULL)
+        {
+            /* request more data _before_ running out of data (requesting
+             * more after the fact prevents speex from successful decoding)
+             * place a hint telling the callback how much of the
+             * previous buffer we have consumed such that it can rewind
+             * as necessary */
+            int bitPtr = td->bits.bitPtr;
+            td->vi.size = td->bits.charPtr;
+            td->vi.get_more(&td->vi.start, &td->vi.size);
+            speex_bits_set_bit_buffer(&td->bits, (void *)td->vi.start,
+                                      td->vi.size);
+            td->bits.bitPtr = bitPtr;
+        }
+
         yield();
 
         /* Output the decoded frame */