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MJPEG Encoding and Web Video Stream Example Explanation

Overview

The MJPEG web video stream example obtains YUV420SP video frames from the Sensor, encodes them into JPEG via the MJPEGEncoder hardware, and continuously transmits them using HTTP multipart/x-mixed-replace. Once a phone or computer is connected to the same network as the development board, the live image can be viewed directly through a browser.

The complete example is located at:

• Development board firmware path: /sdcard/examples/02-Media/mjpeg_web_server.py

• SDK source path: src/canmv/resources/examples/02-Media/mjpeg_web_server.py

Main Configuration

Before running, you need to modify the network parameters at the beginning of the example:

NETWORK_TYPE = "wifi_sta"  # "default", "lan", "wifi_sta" or "wifi_ap"
WLAN_DEVICE = "auto"       # "auto", "usb", "sdio" or "spi"
WIFI_SSID = "Test"
WIFI_PASSWORD = "12345678"
NETWORK_TIMEOUT = 20

SERVER_PORT = 8080
FRAME_WIDTH = 1920
FRAME_HEIGHT = 1080
FRAME_ALIGNMENT = 12
JPEG_QUALITY = 50
STREAM_FPS = 30
USE_VIDEO_FRAME = True

Configuration	Description
NETWORK_TYPE	Select default interface, LAN, Wi-Fi STA, or Wi-Fi AP
WLAN_DEVICE	Select auto, USB, SDIO, or SPI Wi-Fi
NETWORK_TIMEOUT	Timeout for waiting for a network address, in seconds
FRAME_WIDTH, FRAME_HEIGHT	Sensor output and JPEG encoding resolution
FRAME_ALIGNMENT	Sensor image plane alignment exponent; VENC input should be set to 12, i.e., 4096 bytes
JPEG_QUALITY	JPEG quality, ranging from 1 to 99
STREAM_FPS	Upper limit of sending frame rate; the actual frame rate is also limited by encoding speed and network bandwidth
USE_VIDEO_FRAME	True encodes the Sensor video frame directly; keep True for full-HD continuous video streams

The script uses libs.Network.connect_network() to select the dynamically registered network interface, wait for a valid IP, and set the default uplink, without hardcoding the netdev name.

Encoding Process

The Sensor output must use YUV420SP, and ensure that the physical address of each plane is aligned to 4096 bytes:

sensor = Sensor()
sensor.reset()
sensor.set_framesize(
    width=FRAME_WIDTH,
    height=FRAME_HEIGHT,
    alignment=FRAME_ALIGNMENT,
)
sensor.set_pixformat(Sensor.YUV420SP)
sensor.run()

encoder = MJPEGEncoder(quality=JPEG_QUALITY)

For continuous encoding, obtain py_video_frame_info directly:

def capture_jpeg(sensor, encoder):
    frame = sensor.snapshot(dump_frame=True)
    jpeg = encoder.encode(frame, timeout_ms=1000)
    del frame
    return jpeg

This method submits the Sensor’s VB frame directly to VENC, avoiding copying a 1920×1080 image to an intermediate buffer. If you need to demonstrate image.Image input, you can set USE_VIDEO_FRAME to False at a lower resolution.

HTTP Interface

After the example starts, the access address will be printed on the serial port:

Open http://192.168.2.60:8080/ in a browser

Path	Content
/	Live video page
/stream	multipart/x-mixed-replace MJPEG data stream
/snapshot.jpg	Current single-frame JPEG image

The JavaScript in the web page waits 1 second and reconnects to /stream after a video stream connection error, so there is no need to manually refresh the page.

Large Frame Network Transmission

RT-Smart’s blocking socket send timeout is limited to 500 ms. 1080P JPEG is relatively large, so calling sendall() once directly may timeout after TCP send buffer backpressure occurs, causing the browser to display only one frame before disconnecting.

The example keeps the client socket in non-blocking mode, sending JPEG in 16 KiB chunks; it continues to retry when encountering EAGAIN or temporary timeout. As long as sending still progresses, the connection is maintained. The client connection is closed only when there is no sending progress for 5 consecutive seconds.

Running Steps

1. Modify NETWORK_TYPE, WLAN_DEVICE, and Wi-Fi credentials; set NETWORK_TYPE to "lan" when using wired network.

2. Run /sdcard/examples/02-Media/mjpeg_web_server.py.

3. Wait for the serial port to output First JPEG size and the browser access address.

4. Open that address on a phone or computer within the same LAN.

Usage Limitations

• This example uses a synchronous single-client design. When one browser is accessing /stream, the server will not process another client’s request simultaneously.

• STREAM_FPS=30 is the target upper limit and does not guarantee that WLAN can continuously transmit 1080P 30 FPS. When noticeable lag occurs, reduce JPEG_QUALITY, STREAM_FPS, or resolution.

• When the browser consumes data at a rate lower than the generation rate, TCP backpressure will naturally reduce the actual frame rate, without caching JPEG frames indefinitely.

• When exiting the script, the socket, encoder, and Sensor will be closed in order, avoiding leftover VENC channels or VB buffer pools.

For the complete interface description, please refer to the MJPEGEncoder API manual.