一、Player Settings 设置
Player Settings>Player>Other Settings> Android > Write Permission > External (SDCard).

二、代码

using System.Collections;
using System.Collections.Generic;
using System.IO;
using UnityEngine;
using UnityEngine.Android;
using System;
using UnityEngine.UI;
public class VideoPlayManager : MonoBehaviour
{

    private void Awake()
    {
       
    }
    void Start()
    {
        SetAndroid();
       
    }
 
    private void SetAndroid()
    {
#if UNITY_ANDROID
        // 控制音频和视频的权限，在Android设备上需要申请权限
       // Permission.RequestUserPermission(Permission.ExternalStorageRead);
       // Permission.RequestUserPermission(Permission.ExternalStorageWrite);
        if (!Permission.HasUserAuthorizedPermission(Permission.ExternalStorageRead))
        {
            Permission.RequestUserPermission(Permission.ExternalStorageRead);
        }

        //请求 写入外部存储（如 SD 卡）的权限       
        if (!Permission.HasUserAuthorizedPermission(Permission.ExternalStorageWrite))
        {
            Permission.RequestUserPermission(Permission.ExternalStorageWrite);
        }
#endif
    }
}

三、修改AndroidManifest
打开AndroidManifest
Player Settings>Player>Other Settings> Android >Publishing Settings> Build>Custom Main Manifest

在Assets\Plugins\Android\AndroidManifest打开AndroidManifest添加权限代码

	<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" tools:remove="android:maxSdkVersion" />
	<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" tools:remove="android:maxSdkVersion" />