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Contents : Joint Video Team (JVT) of ISO/IEC MPEG & ITU-T VCEG (ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 Q.6) 5th Meeting: Geneva Switzerland 9-17 October 2002 Document: JVT-E133 Filename: JVT-E133.doc Title: Time Shift Causality Constraint on the CAT-LB HRD Status: Input Document to JVT Purpose: Proposal Author(s) or Contact(s): Natan Peterfreund 549 Baltic Way Sunnyvale CA 94089 USA Tel: Email: : +972-4-6230150 natan.peterfreund@harmonicinc.com Source: Harmonic Inc. Abstract: The constraint arrival time leaky bucket model (CAT-LB HRD) imposes a causality constraint on the arrival time of encoded bits to the Pre-decoder buffer. According to this constraint the arrival time of each picture after the first is constrained to arrive at the buffer input no earlier then the difference in hypothetical encoder processing times between that picture and the first picture. We show that given a Leaky Bucket Model (R F B) where F denotes the initial buffering and B the bucket size the causality constraint imposes an upper bound of F on the pre decoder buffer (PDB) level hence limiting the effective buffer size to F B. To enable initial buffering F which is less then B with subsequent PDB levels above that we propose a time shifting CAT-LB HRD model in which the causality constraint is reduced by the shift Td in time between the time of processing of the first picture and the start of bits transmission at the hypothetical encoder side. This method enables low delay pre-buffering (low F) of stored pre-encoded and RT encoded streams with full effective utilization of the entire pre-decoder buffer B (B F). Background: The CAT-LB model imposes a constraint on the initial arrival time of each picture to the pre decoder buffer. Let tai(n) and taf(n) denote the initial and final arrival time of picture n to the pre decoder buffer respectively. According to the causality constraint the initial arrival time of picture n is the later of taf(n-1) and the sum of all preceding pre dec removal delay times as indicated in Equation (A-0): pre dec removal delay(m) (A-0) where tc pre dec removal delay(m) denotes the time difference between removal of picture m-1 to the removal of picture m from the pre-decoder buffer. Note that if due to the above constraint tai(n) taf(n-1) the bit-rate is zeroed along the time interval defined by these points. There are two working modes for the CAT-LB. The VBR case in which (A-0) applies and the bit-rate is zeroed during the period between taf(n-1) and tai(n) and the CBR case in which tai(n) taf(n-1). We consider first the VBR case wherein tai(n) is defined by (A-0). Consider the virtual buffer VB at the hypothetical encoder side wherein the encoded picture n of size dn is inserted into the buffer at the time defined by pre dec removal delay(m) for n 0 (A-1) The buffer is drained at a rate R whenever there are available bits in the buffer. The buffer status VB(n) VB(tn - ) where tn is just prior to tn is given by VB(0) 0 - R tc pre dec removal delay(n) (A-2) The behavior of VB in the continuous time axis is described in figure 1. VB taf(n-1) tai(n) taf(n) tai(n+1) tn+1 tn-1 tn tn+1 Figure 1: The behaviour of VB We shall show that the VB model is equivalent to the constraint (A-0). From the definition of VB it follows that the causality constraint (A-0) holds if we have the above VB model. To prove the other way let as first consider (A-0) with n 1: tai(1) max taf(0) tc pre dec removal delay(1) (A-3) Multiplying and dividing the right side of the equation by the transmission bit rate R the above condition can be re-written as (A-4) . With the condition that the transmission rate R is zeroed between taf(0) and tai(1) (A-4) describes exactly the VB model as illustrated in Figure 1. This could be iterated to n 1 so that the equivalence of (A-0) (with the zero rate constraint between taf(n) and tai(n+1)) and the VB model is proven. In the CBR case wherein taf(n-1) and tai(n) are restricted to be equal we have by (A-0) pre dec removal delay(m) (A-5) One can show that the above constraint applies if and only if 0 (A-6) Which is equivalent to (A-2). It follows that the causality constraint imposes a lower bound constraint on VB both at the CBR and VBR cases. Next we consider the fullness VBV of the PDB. Let where decoding delay denotes the delay between the processing time of a picture at the encoder side and the decoding time of the picture at the PDB. A well known result from the literature on the VBV fullness is (A-7) 0 we have by (A-7) F with VBV(0) F (A-8) where F decoding delay*R In the current HRD model we have decoding delay initial pre dec removal delay where initial pre dec removal delay is a parameter in the buffering period SEI message which denotes the initial buffering delay at the PDB. According to (A-8) in the case of initial pre-buffering F at the PDB which is less than the buffer size B the causality constraint (A-0) limits the effective buffer size to F. In the following we propose a time-shifting approach resulting with an effective buffer size greater than F. In this case for an initial pre-buffering VBV(0) F B the PDB buffer fullness VBV could get up to the buffer size B. Proposal: Consider the case where the start of bit transmission from the hypothetical encoder is delayed in time by D tc for some D 0 with respect to the first picture processing time at the hypothetical encoder. In this case we have decoding delay initial pre dec removal delay + D tc As during the time period 0 D tc we have R(t) 0 then by (A-8) we have F + R D tc with VBV(0) F (A-9) where F R initial pre dec removal delay The new time-shift CAT-LB (A-9) implies that given initial PDB fullness of F the upper bound on the PDB fullness is given by min(F+R tc D B). The behavior of the PDB buffer fullness in this case is illustrated in Figure 2. F+ R tc D F Figure 2: The behavior of the PDB fullness for the time shift CAT-VLC model case. The new proposed time shift causality condition on the time of arrival of picture n which results with the VBV behavior (A-9) is thus given by pre dec removal delay(m) D ) (A-10) for some integer D. This constraint is proposed to replace the condition (C-3) in the H.264 FCD. For practical applications we can consider D in the range of 0 to 7 (i.e. 3bits). The information on the value of D is proposed to be within the buffering period SEI message after initial pre dec removel delay k . IDR Parameters limit For each IDR picture the D parameter should be re-calculated in a way that the sum of the initial pre dec removal delay and D remains constant. Given the parameters of IDR picture n initial pre dec removal delay n and D n D n+1 of the IDR picture n+1 is computed as initial pre dec removal delay n+1 + D n+1 initial pre dec removal delay n + D n Discussion In practical applications the encoded streams are pre-buffered prior to transmission. In other cases we stream stored encoded streams. For these cases this approach enables a relatively low delay streaming imposed by initial buffering less than B while still having an effective pre-decoder buffer of size greater then F which could get up to the decoder buffer size B. A note on the Leaky bucket model: Consider the Leaky Bucket model (R F B) where B denotes the Bucket size (and the hence the PDB) B-F - the initial bucket fullness and R the leak rate. As the Leaky Bucket resembles the mirrored image of the PDB this model imposes an initial buffering F at the PDB. Let tn denote the time where picture n is inserted into the bucket (i.e. dn bits are inserted). The state of the bucket just prior to time tn as defined in the latest FCD of the H.264 standard is LB(0) B - F - R(tn - tn-1) (A-11) B- F or equivalently the fullness of the PDB is less then F for all n. In the case of the proposed time-shift CAT-LB it can be shown that the status of the Leaky bucket is given by LB(0) B - F - R(tn - tn-1) (A-12) (Append for Proposal Documents) JVT Patent Disclosure Form International Telecommunication Union Joint Video Coding Experts Group - Patent Disclosure Form (Typically one per contribution and one per Standard Recommendation) Please send to: JVT Rapporteur Gary Sullivan Microsoft Corp. One Microsoft Way Bldg. 9 Redmond WA 98052-6399 USA Email (preferred): Gary.Sullivan@itu.int Fax: +1 425 706 7329 (+1 425 70MSFAX) This form provides the ITU-T ISO/IEC Joint Video Coding Experts Group (JVT) with information about the patent status of techniques used in or proposed for incorporation in a Recommendation Standard. JVT requires that all technical contributions be accompanied with this form. Anyone with knowledge of any patent affecting the use of JVT work of their own or of any other entity ( third parties ) is strongly encouraged to submit this form as well. This information will be maintained in a living list by JVT during the progress of their work on a best effort basis. If a given technical proposal is not incorporated in a Recommendation Standard the relevant patent information will be removed from the living list . The intent is that the JVT experts should know in advance of any patent issues with particular proposals or techniques so that these may be addressed well before final approval. This is not a binding legal document it is provided to JVT for information only on a best effort good faith basis. Please submit corrected or updated forms if your knowledge or situation changes. This form is not a substitute for the ITU ISO IEC Patent Statement and Licensing Declaration which should be submitted by Patent Holders to the ITU TSB Director and ISO Secretary General before final approval. Submitting Organization or Person: Organization name Harmonic Inc. Mailing address 19 Alon Hatavor St. P.O.Box 3600 Caesarea Industrial Park 38900 Country Israel Contact person Natan Peterfreund Telephone 972-4-6230150 Fax 972-4-6230151 Email natan.peterfreund@harmonicinc.com Place and date of submission Caesarea Israel 10/04/02 Relevant Recommendation Standard and if applicable Contribution: Name (ex: JVT ) JVT Title Contribution number (Form continues on next page) 2.0 The submitter is not aware of having any granted pending or planned patents associated with the technical content of the Recommendation Standard or Contribution. or The submitter (Patent Holder) has granted pending or planned patents associated with the technical content of the Recommendation Standard or Contribution. In which case 2.1 The Patent Holder is prepared to grant on the basis of reciprocity for the above Recommendation Standard a free license to an unrestricted number of applicants on a worldwide non-discriminatory basis to manufacture use and/or sell implementations of the above Recommendation Standard. x 2.2 The Patent Holder is prepared to grant on the basis of reciprocity for the above Recommendation Standard a license to an unrestricted number of applicants on a worldwide non-discriminatory basis and on reasonable terms and conditions to manufacture use and/ or sell implementations of the above Recommendation Standard. 2.3 The Patent Holder is unwilling to grant licenses according to the provisions of either 2.1 2.2 or 2.2.1 above. In this case the following information must be provided as part of this declaration: patent registration/application number an indication of which portions of the Recommendation Standard are affected. a description of the patent claims covering the Recommendation Standard In the case of any box other than 2.0 above please provide the following: Patent number(s)/status Inventor(s)/Assignee(s) Relevance to JVT Any other remarks: (please provide attachments if more space is needed) (form continues on next page) Third party patent information fill in based on your best knowledge of relevant patents granted pending or planned by other people or by organizations other than your own. 3.1 The submitter is not aware of any granted pending or planned patents held by third parties associated with the technical content of the Recommendation Standard or Contribution. 3.2 The submitter believes third parties may have granted pending or planned patents associated with the technical content of the Recommendation Standard or Contribution. For box 3.2 please provide as much information as is known (provide attachments if more space needed) - JVT will attempt to contact third parties to obtain more information: 3rd party name(s) Mailing address Country Contact person Telephone Fax Email Patent number/status Inventor/Assignee Relevance to JVT Any other comments or remarks: File:JVT-EYxx Page: PAGE 1 Date Saved: SAVEDATE @ "yyyy-MM-dd" * MERGEFORMAT 2002-10-08

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