Recording video in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Raspberry Pi camera recording code?

Consider this Python code snippet using the picamera library to record a video for 5 seconds. What will be the output?

Raspberry Pi

import time
from picamera import PiCamera

camera = PiCamera()
camera.start_recording('test_video.h264')
time.sleep(5)
camera.stop_recording()
print('Recording complete')

A No output

B SyntaxError

C RuntimeError: Camera not found

D Recording complete

💡 Hint

Think about what the print statement does after recording stops.

The code records a video for 5 seconds and then prints 'Recording complete'. No errors occur if the camera is connected properly.

🧠 Conceptual

intermediate

Which parameter controls the video resolution in PiCamera?

In the picamera library, which parameter sets the resolution of the recorded video?

A camera.resolution

B camera.framerate

C camera.brightness

D camera.contrast

💡 Hint

Resolution means width and height of the video.

The camera.resolution property sets the width and height of the video frames.

🔧 Debug

advanced

Why does this Raspberry Pi video recording code raise an error?

Look at this code snippet. It raises an error when run. What is the cause?

Raspberry Pi

from picamera import PiCamera
import time

camera = PiCamera()
camera.start_recording('video.h264')
camera.wait_recording(5)
camera.stop_recording()
print('Done')

A time module is not imported

B start_recording requires a file object, not a filename string

C wait_recording is not a method of PiCamera

D stop_recording must be called before wait_recording

💡 Hint

Check the official PiCamera documentation for method names.

The method wait_recording does not exist in PiCamera. The correct method to pause recording is time.sleep().

📝 Syntax

advanced

Which option correctly sets up a 10-second video recording with PiCamera?

Choose the code snippet that correctly records a 10-second video using PiCamera.

A

import time
from picamera import PiCamera
camera = PiCamera()
camera.record('vid.h264', 10)
camera.stop_recording()

B

import time
from picamera import PiCamera
camera = PiCamera()
camera.start_recording('vid.h264')
time.sleep(10)
camera.stop_recording()

C

from picamera import PiCamera
camera = PiCamera()
camera.start_recording('vid.h264')
camera.wait(10)
camera.stop_recording()

D

import time
from picamera import PiCamera
camera = PiCamera()
camera.start_recording('vid.h264')
time.wait(10)
camera.stop_recording()

💡 Hint

Remember to use time.sleep() to pause the program.

Option B uses the correct method start_recording, then pauses with time.sleep(10), and stops recording properly.

🚀 Application

expert

How to save a video in MP4 format using Raspberry Pi camera?

You want to record a video and save it directly as an MP4 file using the Raspberry Pi camera. Which approach is correct?

A Record video as H264 and then use <code>ffmpeg</code> to convert it to MP4 after recording

B Use <code>camera.start_recording('video.mp4')</code> and PiCamera saves MP4 automatically

C Set <code>camera.format = 'mp4'</code> before recording to save directly as MP4

D PiCamera cannot record video; use USB webcam instead

💡 Hint

Think about the default video format PiCamera records and how to convert it.

PiCamera records video in H264 format. To get MP4, you must convert the file using tools like ffmpeg after recording.

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