Video compression

video compression

1. A presentation on video compression and applications Ratul Prosad Roll : ASH1811ME121M Session : 2017-2018 Department of Information and Communication Engineering

2. Presentation layout Concept of video compression Video compression technique Video compression standards A pplications A dvantages D isadvantages

3. Video Visual multimedia source that combines a sequence of images to form a moving picture. The video transmits a signal to a screen and processes the order in which the screen captures should be shown. Videos usually have audio components that correspond with the pictures being shown on the screen.

4. Video Compression Video compression is performed through a video codec that works on one or more compression algorithms. Usually video compression is done by removing repetitive images, sounds and/or scenes from a video. For example, a video may have the same background, image or sound played several times or the data displayed/attached with video file is not that important. Video compression will remove all such data to reduce the video file size . For example : MPEG, MPEG2, MPEG4, MPEG7 etc.

5. Video Compression There are two types of video compression. These are : Lossy video compression : Lossy compression means that the compressed file has less data in it than the original file. Images and sounds that repeat throughout the video might be removed to effectively cut out parts of the video that are seen as unneeded. Lossless video compression : Lossless compression is exactly what it sounds like: the original and the compressed versions are nearly identical. None of the data is lost in the compression process.

6. Raw video contains an immense amount of data Communication and storage capabilities are limited & expensive Enabling communication between devices made by different manufacturers Why video compression is necessary?

7. Video Compression Technique Compression(encoding) is a reversible conversion of data that contains fewer bits. This allows a more efficient storage and transmission of the data. The inverse process is called Decompression(decoding ). Software and Hardware that can encode and decode are called decoders. Both combined form a codec and should not be confused with the terms data container or compression algorithms.

8. Video Compression Technique The process of compression involves applying an algorithm to the source video to create a compressed file that is ready for transmission or storage. To play the compressed file, an inverse algorithm is applied to produce a video that shows virtually the same content as the original source video .

9. Video Compression Technique One approach to compress a video source is to apply the JPEG algorithm to each frame independently. This is known as moving JPEG or MPEG. There are three types of compressed frames : I-frames : Those that are compressed independently P-frame : Predictively coded frame, coded based on previously coded frame B-frame : Bi-directionally predicted frame, coded based on both previous and future coded frames

10. Video Compression Technique Arrows show prediction dependencies between frames

11. Video Compression Technique Exploiting the redundancies : – Temporal : MC-prediction (P and B frames) – Spatial : Block DCT – Color : Color space conversion Scalar quantization of DCT coefficients Zigzag scanning, R unlength and Huffman coding of the nonzero quantized DCT coefficients

12. Video Compression Technique Fig : Video Encoder

13. Video Compression Technique Fig : Video Decoder

14. Video Compression Standards

15. Applications of Video Compression Cable TV distribution Interactive communications – videophone, video conferencing, videotext etc. Digital storage media – CD-ROM, VCD, digital VTR Video-on-demand Broadcasting Video surveillance

16. Video Compression Advantages Occupies less disk space Reading and writing faster File transferring is faster The order of bytes is independent

17. Video Compression Disadvantages Compilation need to be done again for compression Errors may occur while transmitting data The byte or pixel relationship is unknown Need to decompress the previous data