Representing Video Flashcards
What are videos made of?
still frame images, combined with audio
What is the typical frame rate?
24-60 frames per second
What is the aspect ratio?
16:9 typically
What is the resolution for 4K
4096 x 2160 pixels
What is the resolution for Full HD?
1920 x 1080
What is the resolution for HD?
1280 x 720
What is the resolution for SD?
853 x 480
What are the 2 main ways for video compression?
- Spatial (Intra-frame)
- Temporal (Inter-frame)
Spatial refers to which format when saving?
M-JPEG
Temporal refers to which format when saving?
MPEG
What do spatial techniques do?
uses information from within the same frame to reduce file size
What do temporal techniques do?
uses data from nearby frames to reduce file size
What are keyframes/I-frames?
- typically compressed only using spatial techniques
- can be reproduced independently
True or False
I-frames can be inserted automatically at scene changes and /or at regular intervals to preserve quality or streaming, or playback
True
What are P and B frames?
P = Predictive
B = Bidirectional
True or False
P and B frames are encoded by saving the difference between them and the previous key frames
True
True or False
If a key frame is lost during streaming or skipped when skipping forwards or backwards, the display video can be distorted.
True
What are the 4 codecs used in video compression?
- HuffYUV
- MPEG-2
- H.264
- H265 (HEVC)
Which of the 4 codecs uses lossy compression techniques?
MPEG-2 and H.264
Which of the 4 codecs uses lossless compression techniques?
HuffYUV
What is the compression ratio for the Huffman compression technique?
74%
What is the compression ratio for the MPEG-2 compression technique?
3.3%
What is the compression ratio for the H.264 compression technique?
1.6%
What is the compression ratio for the H.265 compression technique?
50%
How does MPEG-2 use lossy techniques?
- Temporal and spatial compression
- Huffman encoding
- Highly dependent on bitrate and other encoding options
How does MPEG-2 use lossy techniques?
- Temporal and spatial compression
- Frame prediction
- Predicts the next frame using the spatial and temporal information and compares it with the actual frames, and then saves only the difference
Which has a better perceived quality, MPEG-2 or H.264 at the same bitrate?
H.264
True or False
H.265 often drains the battery faster
True
File containers combine what?
A video stream and an audio stream into one file
Can file containers always use codecs?
Not always
What are 3 file extensions that can indicate file containers?
- avi (audio video interleave)
- mp4 (MPEG-4)
- mkv (Matroska)
What are the attributes for avi?
very old and not good for streaming
What are the attributes of MP4?
- supports multiple audio/video streams and subtitles
- limited codecs
- very popular on mobile devices
What are the attributes of MKV?
- supports unlimited streams
- supports unlimited codecs
- Support on mobile devices varies
