avformat/rtmppkt: add ff_amf_write_array for write

Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavformat/rtmppkt.c

@@ -40,6 +40,12 @@ void ff_amf_write_number(uint8_t **dst, double val)
     bytestream_put_be64(dst, av_double2int(val));
 }
 
+void ff_amf_write_array_start(uint8_t **dst, uint32_t length)
+{
+    bytestream_put_byte(dst, AMF_DATA_TYPE_ARRAY);
+    bytestream_put_be32(dst, length);
+}
+
 void ff_amf_write_string(uint8_t **dst, const char *str)
 {
     bytestream_put_byte(dst, AMF_DATA_TYPE_STRING);

libavformat/rtmppkt.h

@@ -244,6 +244,14 @@ void ff_amf_write_null(uint8_t **dst);
  */
 void ff_amf_write_object_start(uint8_t **dst);
 
+/**
+ * Write marker and length for AMF array to buffer.
+ *
+ * @param dst pointer to the input buffer (will be modified)
+ * @param length value to write
+ */
+void ff_amf_write_array_start(uint8_t **dst, uint32_t length);
+
 /**
  * Write string used as field name in AMF object to buffer.
  *