bluetooth/gst: Determine PA input/output caps in generic code

Make the code ever so slightly more generic by not using appsrc and
appsink in codec-specific logic when assigning caps specific to the raw
(PCM) format provided by or returned to PA.

Note that caps have to be set (= event) after starting, can't send
events in flushing state.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/484>

src/modules/bluetooth/a2dp-codec-aptx-gst.c

@@ -342,16 +342,6 @@ bool gst_init_aptx(struct gst_info *info, pa_sample_spec *ss, bool for_encoding)
             goto fail;
         }
 
-        caps = gst_caps_new_simple("audio/x-raw",
-                "format", G_TYPE_STRING, "S24LE",
-                "rate", G_TYPE_INT, (int) ss->rate,
-                "channels", G_TYPE_INT, (int) ss->channels,
-                "channel-mask", G_TYPE_INT, 0,
-                "layout", G_TYPE_STRING, "interleaved",
-                NULL);
-        g_object_set(info->enc_src, "caps", caps, NULL);
-        gst_caps_unref(caps);
-
         caps = gst_caps_new_simple(aptx_codec_media_type,
                 "rate", G_TYPE_INT, (int) ss->rate,
                 "channels", G_TYPE_INT, (int) ss->channels,
@@ -386,15 +376,6 @@ bool gst_init_aptx(struct gst_info *info, pa_sample_spec *ss, bool for_encoding)
         g_object_set(info->dec_src, "caps", caps, NULL);
         gst_caps_unref(caps);
 
-        caps = gst_caps_new_simple("audio/x-raw",
-                "format", G_TYPE_STRING, "S24LE",
-                "rate", G_TYPE_INT, (int) ss->rate,
-                "channels", G_TYPE_INT, (int) ss->channels,
-                "layout", G_TYPE_STRING, "interleaved",
-                NULL);
-        g_object_set(info->dec_sink, "caps", caps, NULL);
-        gst_caps_unref(caps);
-
         info->dec_bin = gst_bin_new("aptx_dec_bin");
         pa_assert(info->dec_bin);
 

src/modules/bluetooth/a2dp-codec-gst.c

@@ -306,13 +306,63 @@ static GstPadProbeReturn gst_decoder_buffer_probe(GstPad *pad, GstPadProbeInfo *
     return GST_PAD_PROBE_OK;
 }
 
+static GstCaps *gst_create_caps_from_sample_spec(const pa_sample_spec *ss) {
+    gchar *sample_format;
+    GstCaps *caps;
+    int channel_mask;
+
+    switch (ss->format) {
+        case PA_SAMPLE_S16LE:
+            sample_format = "S16LE";
+            break;
+        case PA_SAMPLE_S24LE:
+            sample_format = "S24LE";
+            break;
+        case PA_SAMPLE_S32LE:
+            sample_format = "S32LE";
+            break;
+        default:
+            pa_assert_not_reached();
+            break;
+    }
+
+    switch (ss->channels) {
+        case 1:
+            channel_mask = 0x1;
+            break;
+        case 2:
+            channel_mask = 0x3;
+            break;
+        default:
+            pa_assert_not_reached();
+            break;
+    }
+
+    caps = gst_caps_new_simple("audio/x-raw",
+            "format", G_TYPE_STRING, sample_format,
+            "rate", G_TYPE_INT, (int) ss->rate,
+            "channels", G_TYPE_INT, (int) ss->channels,
+            "channel-mask", GST_TYPE_BITMASK, channel_mask,
+            "layout", G_TYPE_STRING, "interleaved",
+            NULL);
+
+    pa_assert(caps);
+    return caps;
+}
+
 bool gst_codec_init(struct gst_info *info, bool for_encoding) {
     GstPad *pad;
+    GstCaps *caps;
 
     info->seq_num = 0;
 
+    caps = gst_create_caps_from_sample_spec(info->ss);
+
     /* In case if we ever have a codec which supports decoding but not encoding */
     if (for_encoding && info->enc_bin) {
+        g_object_set(info->enc_src, "caps", caps, NULL);
+        gst_caps_unref(caps);
+
         gst_bin_add_many(GST_BIN(info->enc_pipeline), info->enc_src, info->enc_bin, info->enc_sink, NULL);
 
         if (!gst_element_link_many(info->enc_src, info->enc_bin, info->enc_sink, NULL)) {
@@ -330,6 +380,9 @@ bool gst_codec_init(struct gst_info *info, bool for_encoding) {
         gst_pad_add_probe(pad, GST_PAD_PROBE_TYPE_BUFFER, gst_encoder_buffer_probe, info, NULL);
         gst_object_unref(pad);
     } else if (!for_encoding && info->dec_bin) {
+        g_object_set(info->dec_sink, "caps", caps, NULL);
+        gst_caps_unref(caps);
+
         gst_bin_add_many(GST_BIN(info->dec_pipeline), info->dec_src, info->dec_bin, info->dec_sink, NULL);
 
         if (!gst_element_link_many(info->dec_src, info->dec_bin, info->dec_sink, NULL)) {

src/modules/bluetooth/a2dp-codec-ldac-gst.c

@@ -201,7 +201,6 @@ static uint8_t fill_preferred_configuration(const pa_sample_spec *default_sample
 bool gst_init_ldac(struct gst_info *info, pa_sample_spec *ss, bool for_encoding) {
     GstElement *rtpldacpay;
     GstElement *enc;
-    GstCaps *caps;
     GstPad *pad;
 
     if (!for_encoding) {
@@ -264,16 +263,6 @@ bool gst_init_ldac(struct gst_info *info, pa_sample_spec *ss, bool for_encoding)
             goto fail;
     }
 
-    caps = gst_caps_new_simple("audio/x-raw",
-            "format", G_TYPE_STRING, "S32LE",
-            "rate", G_TYPE_INT, (int) ss->rate,
-            "channels", G_TYPE_INT, (int) ss->channels,
-            "channel-mask", G_TYPE_INT, 0,
-            "layout", G_TYPE_STRING, "interleaved",
-            NULL);
-    g_object_set(info->enc_src, "caps", caps, NULL);
-    gst_caps_unref(caps);
-
     rtpldacpay = gst_element_factory_make("rtpldacpay", "rtp_ldac_pay");
     if (!rtpldacpay) {
         pa_log_error("Could not create RTP LDAC payloader element");