Recording video in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic command to start recording a video using the Raspberry Pi camera module?

The basic command is raspivid -o video.h264 -t 10000, which records a 10-second video and saves it as video.h264.

beginner

What does the -t option specify in the raspivid command?

The -t option sets the recording time in milliseconds. For example, -t 10000 records for 10 seconds.

intermediate

How can you record a video with a specific resolution using Raspberry Pi camera?

Use the -w and -h options with raspivid to set width and height. For example, raspivid -o video.h264 -t 5000 -w 1280 -h 720 records a 720p video.

beginner

What file format does raspivid save videos in by default?

raspivid saves videos in the raw H.264 format by default, which can be played or converted to other formats like MP4.

intermediate

How do you convert a raw H.264 video file to MP4 on Raspberry Pi?

You can use MP4Box with the command MP4Box -add video.h264 video.mp4 to convert the raw video to MP4 format.

Which command starts recording a 5-second video on Raspberry Pi?

A raspivid -o video.h264 -t 50000

B raspivid -o video.h264 -t 50

C raspivid -o video.h264

D raspivid -o video.h264 -t 5000

The -t 5000 option records for 5000 milliseconds, which is 5 seconds.

What does the -o option specify in the raspivid command?

A Recording time

B Video resolution

C Output file name

D Frame rate

The -o option sets the output file name for the recorded video.

Which format does raspivid save videos in by default?

A H.264

B AVI

C MOV

D MP4

raspivid saves videos in raw H.264 format by default.

How do you specify the video resolution to 1920x1080 in raspivid?

A -w 1920 -h 1080

B -r 1920 -c 1080

C -res 1920x1080

D -size 1920 1080

Use -w for width and -h for height to set resolution.

Which tool converts raw H.264 video to MP4 on Raspberry Pi?

A ffmpeg

B MP4Box

C raspivid

D vlc

MP4Box is commonly used to convert raw H.264 files to MP4 format.

Explain how to record a 10-second video at 1280x720 resolution using Raspberry Pi camera.

Think about the options needed to set file name, time, and resolution.

Describe the steps to convert a raw H.264 video file to MP4 format on Raspberry Pi.

Consider why raw H.264 might need conversion for easier playback.

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