ESP32-CAM_MJPEG2SD

ESP32 Camera extension to record JPEGs to SD card as MJPEG files and playback to browser.

Files uploaded by FTP are optionally converted to AVI format to allow recordings to replay at correct frame rate on media players.

Purpose

The MJPEG format contains the original JPEG images but displays them as a video. MJPEG playback is not inherently rate controlled, but the app attempts to play back at the MJPEG recording rate. MJPEG files can also be played on video apps or converted into rate controlled AVI or MKV files etc.

Saving a set of JPEGs as a single file is faster than as individual files and is easier to manage, particularly for small image sizes. Actual rate depends on quality and size of SD card and complexity and quality of images. A no-name 4GB SDHC labelled as Class 6 was 3 times slower than a genuine Sandisk 4GB SDHC Class 2. The following recording rates were achieved on a freshly formatted Sandisk 4GB SDHC Class 2 using SD_MMC 1 line mode on a AI Thinker OV2640 board, set to maximum JPEG quality and the configuration given in the To maximise rate section below.

Frame Size	OV2640 camera max fps	mjpeg2sd max fps	Detection time ms
QQVGA	50	35	20
HQVGA	50	30	40
QVGA	50	25	70
CIF	50	20	110
VGA	25	15	80
SVGA	25	10	120
XGA	6.25	6	180
SXGA	6.25	4	300
UXGA	6.25	2	450

Design

The ESP32 Cam module has 4MB of pSRAM which is used to buffer the camera frames and the construction of the MJPEG file to minimise the number of SD file writes, and optimise the writes by aligning them with the SD card cluster size. For playback the MJPEG is read from SD into a cluster sized buffer, and sent to the browser as timed individual frames.

The SD card can be used in either MMC 1 line mode (default) or MMC 4 line mode. The MMC 1 line mode is practically as fast as MMC 4 line and frees up pin 4 (connected to onboard Lamp), and pin 12 which can be used for eg a PIR.

The MJPEG files are named using a date time format YYYYMMDD_HHMMSS, with added frame size, recording rate, duration and frame count, eg 20200130_201015_VGA_15_60_900.mjpeg, and stored in a per day folder YYYYMMDD.
The ESP32 time is set from an NTP server. Define a different timezone as appropriate inmjpeg2sd.cpp.

Installation and Use

Download files into the Arduino IDE sketch location, removing -master from the folder name.
The included sketch ESP32-CAM_MJPEG2SD.ino is derived from the CameraWebServer.ino example sketch included in the Arduino ESP32 library. Additional code has been added to the original file app_httpd.cpp to handle the extra browser options, and an additional filemjpeg2sd.cpp contains the SD handling code. The web page content in camera_index.h has been updated to include additional functions. The face detection code has been removed to reduce the sketch size to allow OTA updates.

To set the recording parameters, additional options are provided on the camera index page, where:

Frame Rate is the required frames per second
Min Frames is the minimum number of frames to be captured or the file is deleted
Verbose if checked outputs additional logging to the serial monitor

An MJPEG recording is generated by holding a given pin high (kept low by internal pulldown when released).
The pin to use is:

pin 12 when in 1 line mode
pin 33 when in 4 line mode

An MJPEG recording can also be generated by the camera itself detecting motion as given in the Motion detection by Camera section below.

If recording occurs whilst also live streaming to browser, the frame rate will be slower.

To play back a recording, select the file using Select folder / file on the browser to select the day folder then the required MJPEG file. After selecting the MJPEG file, press Start Stream button to playback the recording. The recorded playback rate can be changed during replay by changing the FPS value. After playback finished, press Stop Stream button. If a recording is started during a playback, playback will stop.

The following functions are provided by @gemi254.

Entire folders or files within folders can be deleted by selecting the required file or folder from the drop down list then pressing the Delete button and confirming.
Entire folders or files within folders can be uploaded to a remote server via FTP by selecting the required file or folder from the drop down list then pressing the FTP Upload button.
The FTP, Wifi, and other parameters ned to be defined in file myConfig.h, and can also be modified via the browser under Other Settings.

Browser functions only tested on Chrome.

To maximise rate

To get the maximum frame rate on OV2640, in ESP32-CAM_MJPEG2SD.ino:

config.xclk_freq_hz = 10000000; This is faster than the default 20000000
config.fb_count = 8 to provide sufficient buffering between SD writes for smaller frame sizes

In mjpeg2sd.cpp change #define CLUSTERSIZE 32768 if the SD card cluster size is not 32kB.

Motion detection by Camera

An MJPEG recording can also be generated by the camera itself detecting motion using the motionDetect.cpp file.
JPEG images of any size are retrieved from the camera and 1 in N images are sampled on the fly for movement by decoding them to very small grayscale bitmap images which are compared to the previous sample. The small sizes provide smoothing to remove artefacts and reduce processing time.

For movement detection a high sample rate of 1 in 2 is used. When movement has been detected, the rate for checking for movement stop is reduced to 1 in 10 so that the JPEGs can be captured with only a small overhead. The Detection time ms table shows typical time in millis to decode and analyse a frame retrieved from the OV2640 camera.

To enable motion detection by camera, in mjpeg2sd.cpp set #define USE_MOTION true

Additional options are provided on the camera index page, where:

Motion Sensitivity sets a threshold for movement detection, higher is more sensitive.
Show Motion if enabled and the Start Stream button pressed, shows images of how movement is detected for calibration purposes. Gray pixels show movement, which turn to black if the motion threshold is reached.

The motionDetect.cpp file contains additional documented monitoring parameters that can be modified.