Resolve "Kara length"

Closes #58 (closed)

inc/lektor/mkv.h

@@ -47,6 +47,10 @@ struct kara {
    Returns 0 on success and -1 on error. */
 int kara_metadata_read(struct kara_metadata *dst, const char *filename);
 
+/* Reads the duration of the .mkv file `filename`. Returns 0 on success
+   and -1 on error. */
+int kara_read_length(size_t *len, const char *filename);
+
 /* Write metadata to a mkv file. Returns 0 on success and -1 on error */
 int kara_metadata_write(struct kara_metadata *mdt, const char *filename, const char *mkvpropedit);