mpeg: (moving pictures expert group) a video compression standard for multimedia applications seo...
TRANSCRIPT
MPEG: (Moving Pictures Expert Group)A Video Compression Standard for
Multimedia Applications
Seo Yeong Geon
Dept. of Computer Science in GNU
MPEG Overview
• MPEG-1 : a standard for storage and retrieval of
moving pictures and audio on storage media
• MPEG-2 : a standard for digital television
• MPEG-3 : Originally developed for HDTV, but abandoned when MPEG-2 was determined to be sufficient
• MPEG-4 : a standard for multimedia applications
• MPEG-7 : a content representation standard for
information search
• MPEG-21: offers metadata information for audio and
video files
Relevant Standards
• Joint picture Experts Group (JPEG)– Compress still images only
• Expert Group on Visual Telephony (H.261)– Compress sequence of images– Over ISDN (64 kbits/sec)– Low-delay
• Other high-bandwidth “H” standards:• H21 (34 Mbits/sec)• H22 (45 Mbits/sec)
5 Parts of MPEG 1
• Part 1: Combining video and audio inputs into a single/multiple
data stream
• Part 2: Video Compression
• Part 3: Audio Compression
• Part 4: Requirements Verification
• Part 5: Technical report on the software implementation of the
Parts 1 - 3
10 Parts of MPEG-2
• Part 1Part 1:: Combine video and audio data into single/multiple streams
• Part 2:Part 2: Offers more advanced video compression tools
• Part 3:Part 3: Is a multi-channel extension of the MPEG-1 Audio standard
• Part 4/5:Part 4/5: Correspond to and build on part 4/5 of MPEG-1
• Part 6:Part 6: Specifies protocols of managing MPEG-1 & MPEG-2 bitstreams
• Part 7:Part 7: Specifies a multi-channel audio coding algorithm
• Part 8:Part 8: (was discontinued because of obsolescence)
• Part 9: Part 9: specifies the Real-time Interface (RTI) to Transport Stream
decoders
• Part 10:Part 10: the conformance part of Digital Storage Media Command and
Control (currently under development)
MPEG video spatial domain processing
• Spatial domain handled very similarly to JPEG– Convert RGB values to YUV colorspace– Split frame into 8x8 blocks– 2-D DCT on each block– Quantization of DCT coefficients– Run length and entropy coding
Spatial Redundancy Reduction
Zig-Zag Scan,Run-length
coding
Quantization• major reduction• controls ‘quality’
“Intra-FrameEncoded”
Types of frames
• I frame (intra-coded)– Coded without reference to other frames
• P frame (predictive-coded)– Coded with reference to a previous reference frame
(either I or P)– Size is usually about 1/3rd of an I frame
• B frame (bi-directional predictive-coded)– Coded with reference to both previous and future
reference frames (either I or P)– Size is usually about 1/6th of an I frame
Group of Pictures (GOP)
• Starts with an I-frame
• Ends with frame right before next I-frame
• “Open” ends in B-frame, “Closed” in P-frame– (What is the difference?)
• MPEG Encoding parameter, but ‘typical’:– I B B P B B P B B I– I B B P B B P B B P B B I
• Why not have all P and
B frames?
Temporal Redundancy Reduction
• I frames are independently encoded
• P frames are based on previous I, P frames
• B frames are based on previous and following I and P frames– In case something is uncovered
MPEG audio• MPEG-1 – 3 layers of increasing quality, layer 3 being the most
common (MP3)– 16 bits– Samping rate - 32, 44.1, or 48 kHz– Bitrate – 32 to 320 kbps– De facto - 44.1 kHz sample rate, 192 kbps bitrate
• MPEG-2 – Supports > 2 channels, lower sampling frequencies, low bitrate improvement
• AAC (Advanced Audio Coding) – More sample frequencies (8 kHz to 96 kHz)– Higher coding efficiency and simpler filterbank– 96 kbps AAC sounds better than 128 kbps MP3
• Usually CBR, but can do VBR