record.md

title	update
MaixPy Video Record	date author version content 2024-05-20 lxowalle 1.0.0 Initial document

Introduction

This document provides instructions on how to use the video recording feature

Example 1

An example of recording a video in h265 format.

from maix import video, image, camera, app, time

cam = camera.Camera(640, 480, image.Format.FMT_YVU420SP)
e = video.Encoder()
f = open('/root/output.h265', 'wb')

record_ms = 2000
start_ms = time.ticks_ms()
while not app.need_exit():
    img = cam.read()
    frame = e.encode(img)

    print(frame.size())
    f.write(frame.to_bytes())

    if time.ticks_ms() - start_ms > record_ms:
        app.set_exit_flag(True)

步骤：

1. import module and Initialize the camera

   from maix import video, image, camera, app, time
   cam = camera.Camera(640, 480, image.Format.FMT_YVU420SP)

   • camera.Camera() is used to initialise the camera, here the camera resolution is initialised to 640x480, currently the Encoder only supports the NV21 format, so set the image format to image.Format.FMT_YVU420SP.

2. Initialise the Encoder module

   e = video.Encoder()

   • The video.Encoder() module currently only supports processing image.Format.FMT_YVU420SP format images, which supports h265 and h264 encoding, and defaults to h265 encoding. If you want to use h264 encoding, then you can change the initialisation parameter to video.Encoder(type=video.VideoType.VIDEO_H264_CBR).
   • Note that only one encoder can exist at the same time

3. Encoding the camera image

   img = cam.read()
   frame = e.encode(img)

   • img = cam.read() read camera image and save to img
   • frame = e.encode(img) encode img and save result to frame

4. Save the encoded result to file

   f = open('/root/output.h265', 'wb')
   f.write(frame.to_bytes(False))

   • f = open(xxx) opens and creates a file
   • f.write(frame.to_bytes(False)) converts the encoding result frame to type bytes and then calls f.write() to write the data to the file

5. Timed 2s exit

   record_ms = 2000
   start_ms = time.ticks_ms()
   while not app.need_exit():
       if time.ticks_ms() - start_ms > record_ms:
       app.set_exit_flag(True)

   • Here is the application logic for the timed exit, see the code for yourself

6. Done

Example 2

An example of recording a video in h265 format.

from maix import video, time, image, camera, app

cam = camera.Camera(640, 480, image.Format.FMT_YVU420SP)
e = video.Encoder(capture = True)
e.bind_camera(cam)

f = open('/root/output.h265', 'wb')

record_ms = 2000
start_ms = time.ticks_ms()
while not app.need_exit():
    frame = e.encode()
    img = e.capture()

    print(frame.size())
    f.write(frame.to_bytes(True))

    if time.ticks_ms() - start_ms > record_ms:
        app.set_exit_flag(True)

Similar to example 1, the difference is that the Encoder object's bind_camera method is called, and the Encoder takes the initiative to get the camera image, which has the advantage of using the hardware features to increase the encoding speed.

e = video.Encoder(capture = True)
e.bind_camera(cam)
frame = e.encode()
img = e.capture()

• e = video.Encoder(capture = True) enables the capture parameter to allow encoding to capture encoded images when encoding
• e.bind_camera(cam) binds the camera to the Encoder object
• frame = e.encode() Instead of passing in img when encoding, fetch the image from the camera internally
• img = e.capture() captures the encoded image from the Encoder object, which can be used for image processing

Convert to MP4 format

If you want to record video in mp4 format, you can record H265 video first, and then use the ffmpeg tool in the system to convert to mp4 format.

import os

# Pack h265 to mp4
# /root/output.h265 is the h265 file path
# /root/output.mp4 is the mp4 file path
os.system('ffmpeg -loglevel quiet -i /root/output.h265 -c:v copy -c:a copy /root/output.mp4 -y')