Recording video in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start recording video using the PiCamera.

Raspberry Pi

from picamera import PiCamera
camera = PiCamera()
camera.[1]('video.h264')

Drag options to blanks, or click blank then click option'

Acapture

Bstop_recording

Cstart_recording

Dpreview

Attempts:

3 left

💡 Hint

Common Mistakes

Using stop_recording instead of start_recording.

Using capture which is for photos, not video.

The start_recording method begins recording video to the specified file.

2fill in blank

medium

Complete the code to stop recording video.

Raspberry Pi

from picamera import PiCamera
camera = PiCamera()
camera.start_recording('video.h264')
# After some time
camera.[1]()

Drag options to blanks, or click blank then click option'

Astop_recording

Bstart_recording

Ccapture

Dwait_recording

Attempts:

3 left

💡 Hint

Common Mistakes

Using start_recording again instead of stop_recording.

Using capture which is for photos.

The stop_recording method stops the video recording.

3fill in blank

hard

Fix the error in the code to record a 5-second video.

Raspberry Pi

from picamera import PiCamera
import time
camera = PiCamera()
camera.start_recording('video.h264')
time.[1](5)
camera.stop_recording()

Drag options to blanks, or click blank then click option'

Adelay

Bsleep

Cpause

Dwait

Attempts:

3 left

💡 Hint

Common Mistakes

Using time.wait or time.pause which do not exist.

Not pausing the program, so recording stops immediately.

The time.sleep(5) pauses the program for 5 seconds while recording.

4fill in blank

hard

Fill both blanks to record a video with resolution 640x480 and framerate 24.

Raspberry Pi

from picamera import PiCamera
camera = PiCamera()
camera.[1] = (640, 480)
camera.[2] = 24
camera.start_recording('video.h264')

Drag options to blanks, or click blank then click option'

Aresolution

Bframerate

Cbrightness

Dcontrast

Attempts:

3 left

💡 Hint

Common Mistakes

Using brightness or contrast instead of resolution or framerate.

Setting properties after starting recording.

Set resolution to (640, 480) and framerate to 24 before recording.

5fill in blank

hard

Fill all three blanks to record a video file named 'myvideo.h264' with resolution 1280x720 and framerate 30.

Raspberry Pi

from picamera import PiCamera
camera = PiCamera()
camera.[1] = (1280, 720)
camera.[2] = 30
camera.start_recording('[3]')

Drag options to blanks, or click blank then click option'

Aresolution

Bframerate

Cmyvideo.h264

Dvideo.h264

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property names.

Using wrong filename string.

Setting properties after starting recording.

Set resolution and framerate properties, then start recording to 'myvideo.h264'.

Practice

1. What is the main function of start_recording() in the picamera library on Raspberry Pi?

easy

A. To pause the video recording

B. To stop the video recording

C. To begin capturing video and save it to a file

D. To preview the camera feed without recording

Solution

1. Step 1: Understand the purpose of start_recording()

   This function initiates the process of capturing video from the camera and saving it to a specified file.

2. Step 2: Differentiate from other functions

   stop_recording() ends the recording, while start_recording() begins it. Previewing is done by start_preview().

3. Final Answer:

   To begin capturing video and save it to a file -> Option C

4. Quick Check:

   start_recording() starts video capture [OK]

Hint: Remember: start_recording() means begin saving video [OK]

Common Mistakes:

• Confusing start_recording() with stop_recording()
• Thinking start_recording() previews video
• Assuming it pauses recording

2. Which of the following is the correct way to stop a video recording using the picamera library?

easy

A. camera.stop()

B. camera.stop_recording()

C. camera.end_recording()

D. camera.finish_recording()

Solution

1. Step 1: Recall the method to stop recording

   The picamera library uses stop_recording() to end video capture.

2. Step 2: Verify method names

   Other options like stop(), end_recording(), or finish_recording() are not valid methods in picamera.

3. Final Answer:

   camera.stop_recording() -> Option B

4. Quick Check:

   Use stop_recording() to end video [OK]

Hint: Stop recording always uses stop_recording() [OK]

Common Mistakes:

• Using stop() instead of stop_recording()
• Confusing method names
• Assuming end_recording() exists

3. What will be the output behavior of this code snippet on Raspberry Pi?

import time
from picamera import PiCamera
camera = PiCamera()
camera.start_recording('video.h264')
time.sleep(5)
camera.stop_recording()

medium

A. Records a 5-second video and saves it as 'video.h264'

B. Records video indefinitely until manually stopped

C. Throws an error because of missing preview

D. Records video but does not save to file

Solution

1. Step 1: Analyze the code flow

   The code starts recording, waits 5 seconds, then stops recording.

2. Step 2: Understand the effect of time.sleep(5)

   This pauses the program for 5 seconds while recording continues, so the video length is 5 seconds.

3. Final Answer:

   Records a 5-second video and saves it as 'video.h264' -> Option A

4. Quick Check:

   sleep(5) controls recording length [OK]

Hint: sleep() pauses recording duration exactly [OK]

Common Mistakes:

• Thinking recording stops immediately
• Assuming preview is required to record
• Believing video is not saved without explicit save

4. Identify the error in this code snippet for recording video on Raspberry Pi:

from picamera import PiCamera
import time
camera = PiCamera()
camera.start_recording('video.h264')
time.wait(3)
camera.stop_recording()

medium

A. stop_recording() should be called before start_recording()

B. Missing camera initialization

C. File name must be .mp4 not .h264

D. Incorrect method name 'time.wait' instead of 'time.sleep'

Solution

1. Step 1: Check the time delay function

   The code uses time.wait(3), but the correct function to pause is time.sleep(3).

2. Step 2: Confirm other parts are correct

   Camera is initialized, start and stop recording are in correct order, and .h264 is a valid format.

3. Final Answer:

   Incorrect method name 'time.wait' instead of 'time.sleep' -> Option D

4. Quick Check:

   Use sleep() to pause, not wait() [OK]

Hint: Use time.sleep() to pause, not time.wait() [OK]

Common Mistakes:

• Using time.wait() instead of time.sleep()
• Thinking .h264 is invalid file extension
• Calling stop_recording() before start_recording()

5. You want to record a video on Raspberry Pi that automatically stops after 10 seconds without using time.sleep(). Which method should you use to control recording duration?

hard

A. Use camera.wait_recording(10) after start_recording()

B. Use time.sleep(10) before start_recording()

C. Call stop_recording() immediately after start_recording()

D. Use camera.record_for(10) method

Solution

1. Step 1: Understand wait_recording() usage

   This method pauses the program while continuing recording, allowing precise control without blocking the whole program.

2. Step 2: Compare with other options

   time.sleep(10) pauses the entire program, stop_recording() immediately stops recording, and record_for() does not exist.

3. Final Answer:

   Use camera.wait_recording(10) after start_recording() -> Option A

4. Quick Check:

   wait_recording() controls duration without sleep [OK]

Hint: Use wait_recording() to record timed video without sleep [OK]

Common Mistakes:

• Using sleep() which blocks whole program
• Calling stop_recording() too soon
• Assuming record_for() method exists