SYNTAX AND SEMANTICS FOR BUFFERING INFORMATION TO SIMPLIFY VIDEO SPLICING
Innovations in syntax and semantics of coded picture buffer removal delay (“CPBRD”) values potentially simplify splicing operations. For example, a video encoder sets a CPBRD value for a current picture that indicates an increment value relative to a nominal coded picture buffer removal time of a preceding picture in decoding order, regardless of whether the preceding picture has a buffering period SEI message. The encoder can signal the CPBRD value according to a single-value approach in which a flag indicates how to interpret the CPBRD value, according to a two-value approach in which another CPBRD value (having a different interpretation) is also signaled, or according to a two-value approach that uses a flag and a delta value. A corresponding video decoder receives and parses the CPBRD value for the current picture. A splicing tool can perform simple concatenation operations to splice bitstreams using CPBRD value for the current picture.
1 . (canceled)
2 . One or more non-transitory computer-readable media having stored thereon computer-executable instructions for causing one or more processing units, when programmed thereby, to perform operations comprising:
receiving a concatenation flag and a coded picture buffer removal delay (“CPBRD”) delta value, the concatenation flag having a given value;
receiving encoded data in a bitstream for a given decoding unit of a given access unit, the given access unit corresponding to a current picture among pictures of a video sequence, wherein the given decoding unit is a subset of the current picture;
determining a nominal coded picture buffer (“CPB”) removal time of a preceding access unit based on a nominal CPB removal time of a last decoding unit of the preceding access unit, the preceding access unit corresponding to a preceding picture among the pictures of the video sequence, wherein the last decoding unit is a subset of the preceding picture;
determining a value of a constraint that ensures that delay is at least as long as delay would be if decoding started at the given access unit; and
determining a nominal CPB removal time based at least in part on a sum of (a) the nominal CPB removal time of the preceding access unit and (b) a product of a clock tick value and a factor, wherein the factor depends on the CPBRD delta value, constrained by the value of the constraint.
3 . The one or more non-transitory computer-readable media of claim 2 , wherein the given decoding unit of the given access unit is a slice of the current picture.
4 . The one or more non-transitory computer-readable media of claim 2 , wherein the current picture is a random access picture.
5 . The one or more non-transitory computer-readable media of claim 2 , wherein the last decoding unit of the preceding access unit is a slice of the preceding picture.
6 . The one or more non-transitory computer-readable media of claim 2 , wherein the factor depends on the higher of the CPBRD delta value and the value of the constraint.
7 . The one or more non-transitory computer-readable media of claim 6 , wherein the CPBRD delta value is signaled as a syntax element representing the CPBRD delta value minus 1.
8 . The one or more non-transitory computer-readable media of claim 2 , wherein the determining the value of the constraint includes combining an initial coded picture buffer removal delay value, divided by 90000, with a final arrival time of the preceding access unit and the nominal CPB removal time of the preceding access unit.
9 . The one or more non-transitory computer-readable media of claim 8 , wherein the determining the value of the constraint further includes dividing a result of the combining by the clock tick value.
10 . The one or more non-transitory computer-readable media of claim 2 , wherein the value of the constraint is determined as Ceil ((InitiCpbRemovalDelay [SchedSelIdx]÷90000+t af (n b )−t r,n (n b ))=t c ), wherein Ceil ( ) is a ceiling function, wherein InitiCpbRemovalDelay [SchedSelIdx] represents an initial coded picture buffer removal delay value, wherein t af (n b ) represents a final arrival time of the preceding access unit, wherein t r,n (n b ) represents the nominal CPB removal time of the preceding access unit, and wherein t c represents the clock tick value.
11 . The one or more non-transitory computer-readable media of claim 2 , wherein:
the current picture is part of a temporal layer, and the preceding picture immediately precedes the current picture in decoding order in the temporal layer of the current picture or a lower temporal layer; or
the preceding picture, among pictures having a temporal identifier of zero, immediately precedes the current picture in decoding order.
12 . The one or more non-transitory computer-readable media of claim 2 , wherein the concatenation flag and the CPBRD delta value are for the given access unit, and wherein the concatenation flag and the CPBRD delta value are signaled as part of a buffering period supplemental enhancement information message associated with the given access unit.
13 . In a computer system, a method comprising:
receiving encoded data in a bitstream for a given decoding unit of a given access unit, the given access unit corresponding to a current picture among pictures of a video sequence, wherein the given decoding unit is a subset of the current picture, the bitstream further including a concatenation flag and a coded picture buffer removal delay (“CPBRD”) delta value, the concatenation flag having a given value; and
storing the bitstream, wherein the bitstream is organized to facilitate decoding with operations comprising:
determining a nominal coded picture buffer (“CPB”) removal time of a preceding access unit based on a nominal CPB removal time of a last decoding unit of the preceding access unit, the preceding access unit corresponding to a preceding picture among the pictures of the video sequence, wherein the last decoding unit is a subset of the preceding picture;
determining a value of a constraint that ensures that delay is at least as long as delay would be if decoding started at the given access unit; and
determining a nominal CPB removal time based at least in part on a sum of (a) the nominal CPB removal time of the preceding access unit and (b) a product of a clock tick value and a factor, wherein the factor depends on the CPBRD delta value, constrained by the value of the constraint.
14 . The method of claim 13 , wherein:
the given decoding unit of the given access unit is a slice of the current picture;
the current picture is a random access picture; and
the last decoding unit of the preceding access unit is a slice of the preceding picture.
15 . The method of claim 13 , wherein the factor depends on the higher of the CPBRD delta value and the value of the constraint, and wherein the CPBRD delta value is signaled as a syntax element representing the CPBRD delta value minus 1.
16 . The method of claim 13 , wherein the determining the value of the constraint includes:
combining an initial coded picture buffer removal delay value, divided by 90000, with a final arrival time of the preceding access unit and the nominal CPB removal time of the preceding access unit; and
dividing a result of the combining by the clock tick value.
17 . The method of claim 13 , wherein:
the current picture is part of a temporal layer, and the preceding picture immediately precedes the current picture in decoding order in the temporal layer of the current picture or a lower temporal layer; or
the preceding picture, among pictures having a temporal identifier of zero, immediately precedes the current picture in decoding order.
18 . The method of claim 13 , wherein the concatenation flag and the CPBRD delta value are for the given access unit, and wherein the concatenation flag and the CPBRD delta value are signaled as part of a buffering period supplemental enhancement information message associated with the given access unit.
19 . In a computer system, a method comprising:
setting a concatenation flag and a coded picture buffer removal delay (“CPBRD”) delta value, the concatenation flag having a given value;
encoding a given decoding unit of a given access unit, the given access unit corresponding to a current picture among pictures of a video sequence, wherein the given decoding unit is a subset of the current picture, thereby producing encoded data for the given decoding unit of the given access unit; and
outputting the encoded data in a bitstream, the bitstream further including the concatenation flag and the CPBRD delta value, thereby enabling a video decoder to perform decoding operations comprising:
determining a nominal coded picture buffer (“CPB”) removal time of a preceding access unit based on a nominal CPB removal time of a last decoding unit of the preceding access unit, the preceding access unit corresponding to a preceding picture among the pictures of the video sequence, wherein the last decoding unit is a subset of the preceding picture;
determining a value of a constraint that ensures that delay is at least as long as delay would be if decoding started at the given access unit; and
determining a nominal CPB removal time based at least in part on a sum of (a) the nominal CPB removal time of the preceding access unit and (b) a product of a clock tick value and a factor, wherein the factor depends on the CPBRD delta value, constrained by the value of the constraint.
20 . The method of claim 19 , wherein:
the given decoding unit of the given access unit is a slice of the current picture;
the current picture is a random access picture; and
the last decoding unit of the preceding access unit is a slice of the preceding picture.
21 . The method of claim 19 , wherein the concatenation flag and the CPBRD delta value are for the given access unit, and wherein the concatenation flag and the CPBRD delta value are signaled as part of a buffering period supplemental enhancement information message associated with the given access unit.