Awesome, you’re already ahead of the game with that Android USB Host app working on U disks! Switching to Raspberry Pi for synchronous video streaming without WiFi or UART is totally doable—here are the most practical, high-bandwidth solutions tailored to your setup:

1. USB CDC (Communications Device Class) with Custom Streaming Protocol #

This is a flexible, low-latency option since CDC is designed for bidirectional byte streams, perfect for video data.

• On Raspberry Pi: Set up USB Gadget mode to emulate a CDC ACM device (think a high-speed virtual serial port). Use the libcomposite kernel module to configure the gadget—you can write a simple shell script to define the CDC interface and assign bulk IN/OUT endpoints for data transfer. Once configured, your Pi can push compressed video frames (like H.264) through the bulk endpoint in real time.
• On Android: Build on your existing USB Host code to detect the CDC device, request permissions, and establish a UsbDeviceConnection. Use bulkTransfer() to read incoming video frames from the Pi’s bulk IN endpoint. To keep sync, wrap each frame in a small header (e.g., 4-byte frame length + frame data) so your app knows exactly where one frame ends and the next begins.

2. Emulated USB Mass Storage with Real-Time File Streaming #

If you want to reuse most of your existing U disk reading code, this is a quick win for prototyping.

• On Raspberry Pi: Use FUSE (Filesystem in Userspace) to create a virtual file that acts like a regular file on a USB drive, but feeds directly from your live video stream. Tools like fusepy or custom FUSE scripts can pipe video data into this virtual file as it’s generated. Then enable USB Gadget mode to expose this virtual filesystem as a USB mass storage device.
• On Android: Modify your existing code to continuously read from a specific file on the "U disk" (the Pi’s emulated storage). Note that this has slightly higher latency than CDC since it uses the storage protocol, but it’s great for testing without rewriting your core USB Host logic.

3. USB Video Class (UVC) Gadget (Best for Video-Specific Use Cases) #

This is the most purpose-built solution for video streaming, as UVC is the standard protocol for USB cameras—and Android has native support for detecting and reading UVC streams.

• On Raspberry Pi: Enable the uvc-gadget kernel module, which lets the Pi emulate a USB webcam. Pipe your video source (Pi Camera, pre-recorded compressed video, etc.) into the UVC gadget’s video endpoint. There are ready-to-use scripts and utilities to configure resolution, frame rate, and compression settings.
• On Android: Use either a third-party UVC library or roll your own with the USB Host API to connect to the Pi’s UVC device. You can decode H.264 frames directly using Android’s media codecs for smooth, low-latency playback. This leverages Android’s native video pipeline for the best compatibility.

Pro Tips for Success #

• Load Required Kernel Modules: On the Pi, ensure libcomposite, uvc-gadget, and any necessary gadget modules are loaded (add them to /etc/modules to load on boot).
• Compress Video: USB 2.0 has a max bandwidth of ~480 Mbps (real-world is lower)—use H.264 or H.265 compression to avoid bottlenecks.
• Handle USB Permissions: On Android, don’t forget to request android.permission.USB_PERMISSION and handle the permission dialog properly so your app can access the Pi’s USB device.
• Start Small: Test with 720p at 30fps first to validate the connection, then scale up to higher resolutions once you have a stable stream.

内容的提问来源于stack exchange，提问作者Karandeepdps