the DCF specification mandates that a digital camera must store its photos in a "DCIM" directory. DCIM stands for "Digital Camera Images."

The DCIM directory can — and usually does — contain multiple subdirectories. The subdirectories each consist of a unique three-digit number — from 100 to 999 — and five alphanumeric characters. The alphanumeric characters aren’t important, and each camera maker is free to choose their own. For example, Apple is lucky enough to have a five-digit name, so their code is APPLE. On an iPhone, the DCIM directory contains folders like “100APPLE,” “101APPLE,” and so on.

Inside each subdirectory are the image files themselves, which represent the photos you take. Each image file’s name starts with a four-digit alphanumberic code — which can be anything the camera maker wants — followed by a four digit number. For example, you’ll often see files named DSC_0001.jpg, DSC_0002.jpg, and so on. The code doesn’t really matter, but it’s consistent to ensure the photos you take are displayed in the order you took them.

众所周知，Android 文件系统就是一个垃圾场，获得 WRITE_EXTERNAL_STORAGE 或者 MANAGE_EXTERNAL_STORAGE (Adnroid 11) 权限的app可以无限制的读写内部存储空间，就算app使用了推荐的 API 保存照片和视频，文件名也不尽相同。

例如

• QQ | 在QQ中保存的照片、视频（除了通过“我的文件助手”传输的文件外）QQ都会命名为非常奇怪的名字，似乎是MD5值的开头。而且完全没有EXIF数据，难以对照片、视频进行管理
• 微信 | 微信保存的照片视频还算有良心，一般以mmexport开头，后面接一串13位毫秒级的时间戳，比较容易能转换为时间。

• 照片 | IMG_YYYYmmdd_HHMMSS.jpg
• 视频 | VID_YYYYmmdd_HHMMSS.mp4

还要继续适配更多的文件名格式...