238_1_lecture7 - 1 EE 238: Multimedia communications and...

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1 EE 238: Multimedia communications and Multimedia communications and networking networking Prof. Mihaela van der Schaar Prof. Mihaela van der Schaar email: mihaela@ee.ucla.edu email: mihaela@ee.ucla.edu www www - - page: page: medianetlab.ee.ucla.edu medianetlab.ee.ucla.edu
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2 Lecture 7: Lecture 7: Mechanisms for bandwidth Mechanisms for bandwidth adaptation adaptation
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3 Outline Mechanisms for Adapting Compressed Multimedia to Varying Bandwidth Conditions QoS paradigms for multimedia communications Network adaptive media transport Protocols for media transmission Questions/comments/observations are always encouraged, at any point during the lecture!! Encoder Channel (Bit-rate) Buffer Feedback Source
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4 Techniques for bandwidth adaptation At encoding time (live encoding): Rate-control ( we talked already about this ) - Act on source encoding parameters Quantizer selection Coding mode selection Frame type selection Frame skipping At transmission time: Scheduling – future lectures Transcoding – this lecture Bitstream switching – this lecture Scalable coding – this lecture Encoder Channel (Bit-rate) Buffer Feedback Source
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5 Transcoding Transcoding – the conversion of a compressed bitstream to another Main application of transcoding: focused on reducing the bit rate to meet an available channel capacity; conversions between constant bit-rate (CBR) streams and variable bit-rate (VBR) streams to facilitate more efficient transport of video. As the number of networks, types of devices, and content representation formats increase, interoperability between different systems and different networks is becoming more important.
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6 Transcoding
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7 Transcoding for bit-rate reduction The objective of bit-rate reduction is to reduce the bit rate while maintaining low complexity and achieving the highest quality possible. Ideally, the quality of the reduced rate bitstream should have the quality of a bit stream directly generated with the reduced rate. How?
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8 Simplest form of transcoding: Illustration of cascaded pixel-domain transcoding architecture for bit-rate reduction
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9 Simplified transcoding architectures for bit-rate reduction: (a) open-loop, partial decoding to DCT coefficients, then requantize (b) closed-loop, drift compensation for requantized data.
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10 Frame-based comparison of PSNR of the luminance component for cascaded pixel-domain, open-loop, and closed-loop architectures for bit-rate reduction
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11 Spatial Resolution Reduction
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12 Other types of transcoding Temporal resolution reduction Transcoding for error resilience
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13 Bitstream switching – SureStream
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14 Bitstream switching – SP frames
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15 Bitstream switching – SP frames
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16 Problems in Video Streaming over the Internet Problems to be addressed include unknown and dynamic : Bandwidth – Can not reserve bandwidth in Internet today – Available bandwidth is dynamic – If transmit faster than available bandwidth => Congestion occurs, packet loss, and severe drop in
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238_1_lecture7 - 1 EE 238: Multimedia communications and...

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