Fix minor warnings from some of the backend modules and make the configure messages a little more helpful.

audio_dummy.c

@@ -48,7 +48,7 @@ static void start(int sample_rate, __attribute__((unused)) int sample_format) {
   debug(1, "dummy audio output started at Fs=%d Hz\n", sample_rate);
 }
 
-static void play(__attribute__((unused)) short buf[], __attribute__((unused)) int samples) {}
+static void play(__attribute__((unused)) void *buf, __attribute__((unused)) int samples) {}
 
 static void stop(void) { debug(1, "dummy audio stopped\n"); }
 

audio_sndio.c

@@ -33,7 +33,7 @@ static int init(int, char **);
 static void onmove_cb(void *, int);
 static void deinit(void);
 static void start(int, int);
-static void play(short[], int);
+static void play(void *, int);
 static void stop(void);
 static void onmove_cb(void *, int);
 static int delay(long *);
@@ -222,7 +222,7 @@ static void start(__attribute__((unused)) int sample_rate,
   pthread_mutex_unlock(&sndio_mutex);
 }
 
-static void play(short buf[], int frames) {
+static void play(void *buf, int frames) {
   if (frames > 0) {
     pthread_mutex_lock(&sndio_mutex);
     written += sio_write(hdl, buf, frames * framesize);

audio_soundio.c

@@ -167,7 +167,7 @@ static void start(int sample_rate, int sample_format) {
   debug(1, "libsoundio output started\n");
 }
 
-static void play(short buf[], int samples) {
+static void play(void *buf, int samples) {
   // int err;
   int free_bytes = soundio_ring_buffer_free_count(ring_buffer);
   int written_bytes = 0;
@@ -181,7 +181,7 @@ static void play(short buf[], int samples) {
         free_bytes);
 
   if (write_bytes) {
-    memcpy(write_ptr, (char *)buf, write_bytes);
+    memcpy(write_ptr, buf, write_bytes);
     written_bytes += write_bytes;
     soundio_ring_buffer_advance_write_ptr(ring_buffer, write_bytes);
     debug(3, "[<<---] Written to buffer : %d\n", written_bytes);

audio_stdout.c

@@ -43,7 +43,7 @@ static void start(__attribute__((unused)) int sample_rate,
   fd = STDOUT_FILENO;
 }
 
-static void play(short buf[], int samples) {
+static void play(void *buf, int samples) {
   char errorstring[1024];
   int warned = 0;
   int rc = write(fd, buf, samples * 4);

configure.ac

@@ -225,7 +225,7 @@ AC_ARG_WITH(sndio, [  --with-sndio = choose SNDIO API support], [
   AC_MSG_RESULT(>>Including a SNDIO back end)
   HAS_SNDIO=1
   AC_DEFINE([CONFIG_SNDIO], 1, [Needed by the compiler.])
-  AC_CHECK_LIB([sndio], [sio_open], , AC_MSG_ERROR(SNDIO support requires the sndio library!))], )
+  AC_CHECK_LIB([sndio], [sio_open], , AC_MSG_ERROR(SNDIO support requires the sndio library -- libsndio-dev suggested))], )
 AM_CONDITIONAL([USE_SNDIO], [test "x$HAS_SNDIO" = "x1"])
 
 # Look for AO flag
@@ -241,7 +241,7 @@ AC_ARG_WITH(soundio, [  --with-soundio = choose soundio API support.], [
   AC_MSG_RESULT(>>Including an soundio back end)
   HAS_SOUNDIO=1
   AC_DEFINE([CONFIG_SOUNDIO], 1, [Needed by the compiler.])
-  AC_CHECK_LIB([soundio], [soundio_create], , AC_MSG_ERROR(soundio support requires the soundio library!))], )
+  AC_CHECK_LIB([soundio], [soundio_create], , AC_MSG_ERROR(soundio support requires the soundio library -- libsoundio-dev suggested))], )
 AM_CONDITIONAL([USE_SOUNDIO], [test "x$HAS_SOUNDIO" = "x1"])
 
 # Look for pulseaudio flag