Implement shared parsing of INFO tag in Canopus family

Add some bounds checking to CLLC; reduce HQX variable scoping,
add an error message.

libavcodec/canopus.h

@@ -0,0 +1,32 @@
+/*
+ * Canopus common routines
+ * Copyright (c) 2015 Vittorio Giovara <vittorio.giovara@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_CANOPUS_H
+#define AVCODEC_CANOPUS_H
+
+#include <stdint.h>
+
+#include "avcodec.h"
+
+int ff_canopus_parse_info_tag(AVCodecContext *avctx,
+                              const uint8_t *src, size_t size);
+
+#endif /* AVCODEC_CANOPUS_H */