aac: Split function to parse ADTS header data into public and private part

This makes the currently semi-public avpriv_aac_parse_header() function
private to libavcodec and adds a proper public API function to return
the parts of the ADTS header required in libavformat.

libavcodec/adts_parser.c

@@ -0,0 +1,44 @@
+/*
+ * 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
+ */
+
+#include "config.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "adts_header.h"
+#include "adts_parser.h"
+
+int av_adts_header_parse(const uint8_t *buf, uint32_t *samples, uint8_t *frames)
+{
+#if CONFIG_ADTS_HEADER
+    GetBitContext gb;
+    AACADTSHeaderInfo hdr;
+    int err = init_get_bits8(&gb, buf, AV_AAC_ADTS_HEADER_SIZE);
+    if (err < 0)
+        return err;
+    err = ff_adts_header_parse(&gb, &hdr);
+    if (err < 0)
+        return err;
+    *samples = hdr.samples;
+    *frames  = hdr.num_aac_frames;
+    return 0;
+#else
+    return AVERROR(ENOSYS);
+#endif
+}