Existing video streaming applications attempt to provide end users with consistent high quality video streaming. In the presence of network bandwidth variations, this becomes more challenging. Applications that implement multiple bit-rates (MBR) video streaming strive to provide such high quality services by encoding a same video source multiple times at different respective bit-rates. During video streaming operations, an MBR video streaming server or receiver dynamically selects and switches to the bitstream encoded at the proper bit rate in view of current network data throughput conditions to accommodate for bandwidth variations. However, if the bitstreams are switched at an inter-coded P-frame, the switching operations generally introduce drift errors into the resulting video stream, causing reduced video quality. If intra-coded bitstreams are used to switch from one bitstream to another coding efficiency is typically adversely effected (the more intra-coded frames, the less coding efficiency).
To provide “drift(error)-less” bitstream switching, existing MBR video streaming applications may replace original frames of the non-encoded media content with predefined switching frames (e.g. the SP frames in H.264) during encoding operations. Then, based on network bandwidth conditions, the server switches bitstreams at one of these predefined inserted frames. However, replacing normally coded frames (i.e. the inter-coded P-frames) with specially designed switching frames lowers coding efficiency. Moreover, such switching frame replacement operations require data exchange from respective ones of the multiple bitstreams. Thus, in an MBR streaming environment that replaces original frames with predefined switching frames, bitstreams cannot be encoded independent of one or more different bitstreams. Rather, each bitstream is jointly encoded with at least one different bitstream. This increases complexity of the encoding operations. Furthermore, systems that replace normal frames with special switching frames typically fail responsive to transmission errors between the streaming server and receiving device.
Bitstream switching for multiple bit rate video streaming uses a first algorithm to generate multiple encoded bitstreams of a piece of video at different bit rates. A different algorithm is used to generate multiple side bitstreams of the video. Each side stream is generated at respective ones of the different bit rates. The side bitstreams comprise switching frames to switch from a first bitstream encoded with the first algorithm at a first bit rate to a second bitstream encoded with the first algorithm at a different bit rate. At non-bitstream switching points, frames from respective ones of bitstreams generated with the first algorithm are streamed for presentation. At a bitstream switching point, a switching frame from a respective side bitstream is transmitted to a decoder to transition streaming from a first of the respective ones of the bitstreams to a second of the respective ones of the bitstreams.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In the Figures, the left-most digit of a component reference number identifies the particular Figure in which the component first appears.
Overview
There are no existing Wyner-Ziv bitstream switching schemes. Existing Wyner-Ziv coding (not switching) schemes encode entire videos. Such coding schemes have very low coding efficiency and are generally considered unsuitable for non-MBR and MBR video streaming scenarios. In contrast to such existing schemes, systems and methods for bitstream switching in multiple bit-rate (MBR) streaming environments are presented below in reference to
An Exemplary System
Although not required, systems and methods for bitstream switching in MBR video streaming environments are described in the general context of computer-executable instructions executed by a computing device such as a personal computer. Program modules generally include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. While the systems and methods are described in the foregoing context, acts and operations described hereinafter may also be implemented in hardware.
For example, server 102 includes processor 108 coupled to system memory 110. Processor 108 may be a microprocessor, microcomputer, microcontroller, digital signal processor, etc. System memory 110 includes, for example, volatile random access memory (e.g., RAM) and non-volatile read-only memory (e.g., ROM, flash memory, etc.). System memory 110 comprises program modules 112 and program data 114. Program modules 112 include, for example, encoding modules (“encoder”) 116 and “other program modules” 118 such as an Operating System (OS) to provide a runtime environment, a video streaming application that leverages operations of encoder 116, bitstream transmission modules, a conventional and a Wyner-Ziv decoder, a media player, device drivers, and/or so on.
Encoder 116 includes, for example a conventional encoder (e.g., an H.264 encoder) and a Wyner-Ziv encoder. For input signal X (i.e., video data 120), a conventional video encoder produces multiple streams of regular encoded media content 122. Each regularly encoded stream of encoded media content is generated from a same piece of video data 120 and encoded according to a different respective bit transmit rate. The Wyner-Ziv encoding portion of encoder 116 implements any known Wyner-Ziv encoding scheme to produce multiple side streams 124 of encoded media content (i.e., Wyner-Ziv bits) corresponding to the multiple regularly encoded streams. These multiple side streams are also shown as respective portions of encoded media content 126. Each side stream is composed of switching frames; one switching frame per frame of the piece of media content. That is, for at least a subset of frame(s) of X, the Wyner-Ziv encoder produces Wyner-Ziv bits for a respective correlation frame Y for the encoding of X at a bitstream switching point at time n (the time corresponds to a time in a video presentation timeline). These Wyner-Ziv bits are generated independent of any side information frame that will subsequently be generated by client 106 to obtain a target quality for a finally decoded frame.
Encoder 116 (or a video streaming application leveraging operations of encoder 116) communicates frames of the regularly encoded streams 122 to client 106. (Exemplary video transmission module(s) are shown as respective portions of “other program modules” 118). Responsive to receiving frames from a regularly encoded bitstream 122, decoder 128 utilizes a conventional decoder to decode the encoded frames to generate respective portions of decoded content/frames 130). During media content streaming operations, and responsive to determining that bandwidth considerations of network 104 dictate that a first regular encoded bitstream 122 being streamed to client 106 should be switched-out with a different regular coded bitstream 122, encoder 116 transmits a corresponding Wyner-Ziv switching frame (i.e., Wyner-Ziv parity bits) from the side bitstream 124 corresponding to the bitstream 122 being switched-out. The switch-point occurs at time instant n.
In one implementation, responsive to receiving the Wyner-Ziv bits (frame X) from encoder 116, decoder 128 utilizes the Wyner-Ziv portion of decoder 128 to decode the Wyner-Ziv bits and reconstruct a frame X′ of the different regular coded bitstream 122. For example, the received Wyner-Ziv bits and signal Y side information (determined via a conventional request bits feedback loop between decoder 128 and encoder 116) are jointly utilized to decode and output the reconstruction of X, which is represented as X′. At the client, decoded content/frames are presented to a user by media player 132 via display device 134.
Exemplary Operations for Bitstream Switching
In Wyner-Ziv encoding, two correlated signals can be encoded separately, but decoded conditionally. In this implementation, the Wyner-Ziv portion of encoder module(s) 116 implements a turbo code based Wyner-Ziv encoding scheme to facilitate bitstream switching at any desired frame without affecting coding efficiency of regularly transmitted bitstreams. (Although turbo code encoding is known, the described bitstream-switching scheme using Wyner-Ziv bits is novel). Additionally, for any one frame, turbo code based Wyner-Ziv encoding provides for use of a same embedded Wyner-Ziv bitstream for the switching from any other bitstream to the current bitstream.
When server 102 switches between the first bitstream 126 and the second bitstream 126, server 102 transmits only part of the Wyner-Ziv bits in terms of switching point to decoder 128. This partial number of bits provide enough information to correct the errors in the side information generated by decoder 128 using a conventional request-bits feedback loop to generate a good reference frame. In view of this framework, and in this implementation, encoding module(s) 116 implements at least two bitstream switching schemes for MBR video streaming. Before describing these exemplary bitstream-switching schemes, aspects of two exemplary media content encoded bitstreams are described.
Decoder 128 reconstructs frame F2,i using a Wyner-Ziv methodology. The Wyner-Ziv coded parity bits (i.e., side stream) associated with of bitstream 2 are denoted as W2,i. When the bit-streaming operations arrive at the switching point, encoder 116 (or a video streaming application that leverages output of encoder 116) transmits P1,n−1. Then decoder 128 reconstructs F1,n−1 using F1,n−2 as the reference frame. Subsequently, W2,n−1 are transmitted to inform decoder 128 for the purpose of switching. Decoder 128 decodes W2,n−1 using F1,n−1 as the side information. The decoded frame (a bitstream transition frame) F′2,n−1 should be identical or very close to F2,n−1 depending on the quantization step-size in the Wyner-Ziv coding. Following this, encoder 116 transmits subsequent frames P2,n, P2,n+1, . . . to decoder 128. In summary, in this first exemplary scheme for bitstream switching, encoder 116 transmits W2,n−1 and P2,n in total at the switching point to decoder 128. Wyner-Ziv coding is used only at a switching point (E.g., switching occurs at time n, and therefore, conventional encoding and decoding is used until P1,n−1).
Since bitstream 1 is encoded at a lower rate than bitstream 2, the described switch operation represents up-switching from a lower bit rate to a higher bit rate. Wyner-Ziv bits of bitstream 1 (i.e., the parity bits generated by encoder 116) are not needed for up switching.
Exemplary Procedures
Referring to
At block 608, procedure 600 evaluates network bandwidth throughput conditions to determine whether the current encoded bitstream should be switched out with a different encoded bitstream to maintain a high quality video presentation experience to the user. If not, operations continue at block 604. Otherwise, operations of procedure 600 continue at block 610, wherein a different bitstream (a respective bitstream of encoded media content 126) that encoder 116 encoded at a bit-rate appropriate with the current data throughput characteristics of network 104 is identified. At block 612, when the switching point at time n arrives, procedure 600 transmits P1,n−1, referencing a predictive frame in the current bitstream. At block 614, responsive to receiving P1,n−1, decoder 128 reconstructs F1,n−1 using F1,n−2 as the reference frame. At block 616, procedure 600 transmits frame W1,n−1, referencing a Wyner-Ziv frame (i.e., entire frame P2,n) in the second encoded bitstream, to decoder 128 to switch from the first to the second bitstream. At block 618, responsive to receiving W2,n−1, decoder 128 decodes W2,n−1 using F1,n−1 as the side information. At block 620, subsequent frames of the different encoded (e.g., P2,n, P2,n+1, . . . ) are streamed to decoder 128 for decoding and presentation to a user.
Referring to
At block 708, procedure 700 evaluates network bandwidth throughput conditions to determine whether the current encoded bitstream should be switched out with a different encoded bitstream to maintain a high quality video presentation experience to the user. If not, operations continue at block 704. Otherwise, operations of procedure 700 continue at block 710 wherein a different bitstream (a respective bitstream of encoded media content 126) that encoder 116 encoded at a bit-rate appropriate with the current data throughput characteristics of network 104 is identified. At block 712, when the switching point at time n arrives, procedure 700 transmits P1,n−1, referencing a predictive frame in the current bitstream. At block 714, responsive to receiving P1,n−1, decoder 128 reconstructs F1,n−1 using F1,n−2 as the reference frame.
In the exemplary bitstream switching scheme described above in reference to
Although bitstream switching in MBR video streaming environments has been described in language specific to structural features and/or methodological operations or actions, it is understood that the implementations defined in the appended claims are not necessarily limited to the specific features or actions described. Rather, the specific features and operations discussed above with respect to
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