1. An introduction to audio/video compression Prepared by :: Bhatt shivani (130450112002)

2. Introduction Review digital video. Need for compression. Lossy and lossless compression. How to apply techniques to still video (jpeg).

3. Digital Video Samples represent pixel values of a video frame. Typically 480x640x3=1M (approx) per frame Sample size 8-10 bits typically.

4. Video datarates With 8 bits samples at 25 frames per second we have a datarate of 200 Mbits per second. Broadcast video (10 bit and includes audio) 270 Mbits per second.

5. Lossless Compression Achieve datarate reduction without discarding information. Run Length Coding – Eg: 5 5 5 5 5 5 – May be coded 5 6

6. Lossless Compression Entropy (Huffman) Coding Assign shorter codes to the more probable values. Possible when there is statistical bias in image data.

7. Lossy Compression Achieving datarate reduction by discarding information. Missing out samples from data stream/reducing sample size generally noticeable.

8. Example DCT Basis Pictures Picture broken into 8x8 pixel blocks (typically). Any 8x8 pixel (picture) block made by adding different proportions of basis pictures. So store the proportions.

9. DCT basis functions (Basis pictures).

10. Original Picture

11. Using one (dc) basis picture

12. Using 6 basis pictures

13. Video compression Most 8 x 8 blocks do not contain high frequency components. Code high frequency components using less bits (introduces noise).

14. Video compression We are left with a sequence of values. Zig-Zag scan. Many values of zero towards the bottom right hand corner. Use RLE to reduce the datarate further.

15. Thank you …