auhal: prevent revert to unusual formats after SPDIF playback

Getting the current format is unreliable, for instance if the audio
cable is plugged in while playback is running. Thus only the
first original format is trusted.

close #9957

modules/audio_output/auhal.c

@@ -191,6 +191,8 @@ static int Open(vlc_object_t *obj)
     p_sys->b_ignore_streams_changed_callback = false;
     p_sys->b_selected_dev_is_default = false;
     p_sys->b_paused = false;
+    memset(&p_sys->sfmt_revert, 0, sizeof(p_sys->sfmt_revert));
+    p_sys->i_stream_id = 0;
 
     p_aout->sys = p_sys;
     p_aout->start = Start;
@@ -307,7 +309,6 @@ static int Start(audio_output_t *p_aout, audio_sample_format_t *restrict fmt)
     p_sys->au_component = NULL;
     p_sys->au_unit = NULL;
     p_sys->i_hog_pid = -1;
-    p_sys->i_stream_id = 0;
     p_sys->i_stream_index = -1;
     p_sys->b_revert = false;
     p_sys->b_changed_mixing = false;
@@ -716,6 +717,7 @@ static int StartSPDIF(audio_output_t * p_aout, audio_sample_format_t *fmt)
     AudioStreamID           *p_streams = NULL;
     unsigned                i_streams = 0;
     AudioStreamBasicDescription desired_stream_format;
+    memset(&desired_stream_format, 0, sizeof(desired_stream_format));
 
     /* Start doing the SPDIF setup proces */
     p_sys->b_digital = true;
@@ -822,21 +824,37 @@ static int StartSPDIF(audio_output_t * p_aout, audio_sample_format_t *fmt)
             int i_current_rate_format = -1;
             int i_backup_rate_format = -1;
 
-            p_sys->i_stream_id = p_streams[i];
-            p_sys->i_stream_index = i;
-
             if (!p_sys->b_revert) {
                 AudioObjectPropertyAddress currentPhysicalFormatAddress = { kAudioStreamPropertyPhysicalFormat, kAudioObjectPropertyScopeGlobal, kAudioObjectPropertyElementMaster };
                 /* Retrieve the original format of this stream first if not done so already */
-                i_param_size = sizeof(p_sys->sfmt_revert);
-                err = AudioObjectGetPropertyData(p_sys->i_stream_id, &currentPhysicalFormatAddress, 0, NULL, &i_param_size, &p_sys->sfmt_revert);
+                AudioStreamBasicDescription current_streamformat;
+                i_param_size = sizeof(current_streamformat);
+                err = AudioObjectGetPropertyData(p_streams[i], &currentPhysicalFormatAddress, 0, NULL, &i_param_size, &current_streamformat);
                 if (err != noErr) {
                     msg_Err(p_aout, "could not retrieve the original streamformat [%4.4s]", (char *)&err);
                     continue;
                 }
+
+                /* 
+                 * Only the first found format id is accepted. In case of another id later on, we still use the
+                 * already saved one. This can happen if the user plugs in a spdif cable while a stream is already
+                 * playing. Then, auhal already misleadingly reports an ac3 format here whereas the original format
+                 * should be still pcm.
+                 */
+                if (p_sys->sfmt_revert.mFormatID > 0 && p_sys->sfmt_revert.mFormatID != current_streamformat.mFormatID &&
+                        p_streams[i] == p_sys->i_stream_id) {
+                    msg_Warn(p_aout, STREAM_FORMAT_MSG("Detected current stream format: ", current_streamformat));
+                    msg_Warn(p_aout, "... there is another stream format already stored, the current one is ignored");
+                } else {
+                    p_sys->sfmt_revert = current_streamformat;
+                }
+
                 p_sys->b_revert = true;
             }
 
+            p_sys->i_stream_id = p_streams[i];
+            p_sys->i_stream_index = i;
+
             for (int j = 0; j < i_formats; j++) {
                 if (p_format_list[j].mFormat.mFormatID == 'IAC3' ||
                    p_format_list[j].mFormat.mFormatID == 'iac3' ||