First pass at adding transcode support

This does a hard-coded audio encode to vorbis-in-ogg. In the long term,
this should use encodebin and real encoding profiles.

jni/transcode.c

@@ -0,0 +1,91 @@
+#include <gst/gst.h>
+
+#include <jni.h>
+
+static int init(void)
+{
+    /* XXX: ZERO thread-safety guarantees here */
+    static gboolean inited = 0;
+
+    if (inited)
+        return 0;
+
+    gst_init(NULL, NULL);
+    return 0;
+}
+
+static int transcode(const char *infile, const char *outfile,
+        const char *profile)
+{
+    GstElement *pipeline;
+    GstBus *bus;
+    GstMessage *msg;
+    gchar pipeline_str[1024];
+
+    init();
+
+    snprintf(pipeline_str, 1024,
+            "filesrc location=%s ! decodebin2 ! audioconvert ! "
+            "vorbisenc ! oggmux ! filesink location=%s",
+            infile, outfile);
+
+    pipeline = gst_parse_launch(pipeline_str, NULL);
+
+    gst_element_set_state (pipeline, GST_STATE_PLAYING);
+
+    bus = gst_element_get_bus(pipeline);
+    msg = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE,
+            GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
+
+    if (GST_MESSAGE_TYPE(msg) == GST_MESSAGE_ERROR) {
+        GError *err = NULL;
+        gchar *debug_info = NULL;
+
+        gst_message_parse_error(msg, &err, &debug_info);
+
+        GST_ERROR_OBJECT(pipeline, "%s -- %s", err->message,
+                debug_info ? debug_info : "no debug info");
+
+        g_error_free(err);
+        g_free(debug_info);
+    }
+
+    if (msg != NULL)
+        gst_message_unref (msg);
+
+    gst_object_unref (bus);
+    gst_element_set_state (pipeline, GST_STATE_NULL);
+    gst_object_unref (pipeline);
+}
+
+jint Java_org_wikimedia_commons_Transcoder_transcode(JNIEnv* env,
+        jclass *klass, jstring infile, jstring outfile, jstring profile)
+{
+    const char *in;
+    const char *out;
+    const char *prof = NULL;
+
+    if (!infile || !outfile)
+        return -1;
+
+    in = (*env)->GetStringUTFChars(env, infile, 0);
+    out = (*env)->GetStringUTFChars(env, outfile, 0);
+
+    if (profile)
+        prof = (*env)->GetStringUTFChars(env, profile, 0);
+
+    return transcode(in, out, prof);
+}
+
+
+#ifdef TEST
+int main(int argc, char **argv)
+{
+    if (argc != 3)
+        return -1;
+
+    transcode(argv[1], argv[2], NULL);
+
+    return 0;
+}
+#endif