Systems and methods for adjusting targeted bit allocation based on an occupancy level of a VBV buffer model
View Patent ↗Methods and apparatus are provided to advantageously improve bit rate control in a video encoder, such as an MPEG video encoder. The targeted bit allocation for a picture to be encoded is advantageously varied based on an occupancy level of a buffer model, such as a video buffer verifier (VBV) buffer model.
1. A method implemented in computer executable form in a video encoding process for adjusting a targeted bit allocation T for a picture that is to be encoded and transmitted to a decoder, the method comprising:
computing at an encoder a targeted bit allocation T for encoding the picture and storing in an encoder buffer;
determining a threshold from at least one desired occupancy level of a buffer model characterizing a decoder buffer status of the decoder;
adaptively adjusting the targeted bit allocation T at the encoder at least partially in response to a comparison of an occupancy status of the buffer model with the threshold; and
providing the adjusted targeted bit allocation T to the video encoding process, wherein the targeted bit allocation T prior to adaptive adjustment is an original targeted bit allocation T and the threshold is a second threshold, the second threshold corresponds to T high , where T high comprises:
T
high
=
V
status
-
V
high
+
bit_rate
picture_rate
,
where V status is the occupancy status, V high is the desired occupancy level, bit_rate is a bit rate of a transmission channel from the encoder to the decoder and picture_rate is a display rate of pictures, and further comprising:
comparing the original targeted bit allocation T to the second threshold; and
adaptively adjusting the original targeted bit allocation T when the original targeted bit allocation T is below the second threshold but not otherwise.
2. A method implemented in computer executable form in a video encoding process for adjusting a targeted bit allocation T for a picture that is to be encoded and transmitted to a decoder, the method comprising:
computing at an encoder a targeted bit allocation T for encoding the picture and storing in an encoder buffer;
determining a threshold from at least one desired occupancy level of a buffer model characterizing a decoder buffer status of the decoder;
adaptively adjusting the targeted bit allocation T at the encoder at least partially in response to a comparison of an occupancy status of the buffer model with the threshold; and
providing the adjusted targeted bit allocation T to the video encoding process;
the targeted bit allocation T prior to adaptive adjustment is an original targeted bit allocation T and the threshold includes a first threshold and a second threshold, further comprising:
comparing the original targeted bit allocation T to at least one of the first threshold and the second threshold;
adaptively adjusting the original targeted bit allocation T when the original targeted bit allocation T exceeds the first threshold or when the targeted bit allocation T is below the second threshold, but not otherwise,
wherein the first threshold corresponds to T mid and the second threshold corresponds to T high , where T mid and T high further comprise:
T mid =V status −V mid ; and
T
high
=
V
status
-
V
high
+
bit_rate
picture_rate
,
where V status is the occupancy status, V mid is a first one of the at least one desired occupancy level, V high is a second one of the at least one desired occupancy level, bit_rate is a bit rate of a transmission channel from the encoder to the decoder and picture_rate is a display rate of pictures.
3. The method as defined in claim 1 , wherein computing the targeted bit allocation T for I-pictures, for P-pictures, and for B-pictures corresponds to computing T i , T p , and T b , respectively, where T i , T p , and T b further comprise:
T
i
=
max
{
(
R
(
1
+
N
p
X
p
X
i
K
p
+
N
b
X
b
X
i
K
b
)
)
,
(
bit_rate
8
·
picture_rate
)
}
;
T
p
=
max
{
(
R
(
N
p
+
N
b
K
p
X
b
K
b
X
p
)
)
,
(
bit_rate
8
·
picture_rate
)
}
;
and
and
T
b
=
max
{
R
(
N
p
+
N
p
K
b
X
p
K
p
X
b
)
,
bit_rate
8
·
picture_rate
}
,
where R is a remaining number of bits allocated to a group of pictures to which the picture belongs, N p and N b are a number of P-pictures and B-pictures in the group of pictures, respectively, K b and K p are constants associated with complexity matrices for P-pictures and B-pictures, respectively, X i , X p and X b are complexity estimators for I-pictures, P-pictures and B-pictures, respectively, bit_rate is a bit rate of a transmission channel from the encoder to the decoder and picture_rate is a display rate of pictures.
4. A method implemented in computer executable form in a video encoding process for adjusting a targeted bit allocation T for a picture that is to be encoded and transmitted to a decoder, the method comprising:
computing at an encoder a targeted bit allocation T for encoding the picture and storing in an encoder buffer;
determining a threshold from at least one desired occupancy level of a buffer model characterizing a decoder buffer status of the decoder;
adaptively adjusting the targeted bit allocation T at the encoder at least partially in response to a comparison of an occupancy status of the buffer model with the threshold; and
providing the adjusted targeted bit allocation T to the video encoding process, wherein when the picture to be encoded corresponds to a P-picture with a scene change, computing the targeted bit allocation T corresponds to computing T p′ , where T p′ comprises:
T
p
′
=
max
{
(
R
(
1
+
(
N
p
-
1
)
X
p
X
i
K
p
+
N
b
X
b
X
i
K
b
)
)
,
(
bit_rate
8
·
picture_rate
)
}
,
where R is a remaining number of bits allocated to a group of pictures to which the picture belongs, N p and N b are a number of P-pictures and B-pictures in the group of pictures, respectively, K p and K b are constants associated with complexity matrices for P-pictures and B-pictures, respectively, X i , X p and X b are complexity estimators for I-pictures, P-pictures and B-pictures, respectively, bit_rate is a bit rate of a transmission channel from the encoder to the decoder and picture_rate is a display rate of pictures.
5. The method as defined in claim 1 , wherein the buffer model is a virtual buffer verifier (VBV) buffer model.
6. The method as defined in claim 1 , wherein the video encoding process is performed in real time, and where a constant bit rate is used to update a calculation of the buffer occupancy level.
7. The method as defined in claim 1 , further comprising bounding the targeted bit allocation T to a maximum value of T max , where T max comprises:
T max =V status −V low ,
where V status is the occupancy status and V low is a low occupancy level of the buffer model.
8. The method as defined in claim 7 , wherein V low is about ⅜ of a capacity of the buffer model.
9. A method implemented in computer executable form in a video encoding process for adjusting a targeted bit allocation T for a picture that is to be encoded and transmitted to a decoder, the method comprising:
computing at an encoder a targeted bit allocation T for encoding the picture and storing in an encoder buffer;
determining a threshold from at least one desired occupancy level of a buffer model characterizing a decoder buffer status of the decoder;
adaptively adjusting the targeted bit allocation T at the encoder at least partially in response to a comparison of an occupancy status of the buffer model with the threshold; and
providing the adjusted targeted bit allocation T to the video encoding process, further comprising bounding the targeted bit allocation T to a minimum value of T min , where T min comprises:
T
min
=
max
(
V
status
+
bit_rate
picture_rate
-
V
high
,
0
)
,
where V status is the occupancy status, V high is a desired occupancy level, bit_rate is a bit rate of a transmission channel from the encoder to the decoder and picture_rate is a display rate of pictures.
10. The method as defined in claim 9 , where V high is about 63/64 of a capacity of the buffer model.
11. The method as defined in claim 1 , wherein the video encoding process is performed in real time.
12. A method implemented in computer executable form in a video encoding process for calculating a targeted bit allocation T for a picture that is to be encoded and transmitted to a decoder comprising:
computing at an encoder a targeted bit allocation T for encoding the picture and storing in an encoder buffer;
determining a threshold from at least one desired occupancy level of a buffer model characterizing a decoder buffer status of the decoder;
scaling the targeted bit allocation T at the encoder by a factor at least partially in response to a comparison of an occupancy status of the buffer model with the threshold; and
providing the adjusted targeted bit allocation T to the video encoding process, further comprising bounding the targeted bit allocation T to a minimum value of T min , where T min comprises:
T
min
=
max
(
V
status
+
bit_rate
picture_rate
-
V
high
,
0
)
,
where V status is the occupancy status, V high is a desired occupancy level, bit_rate is a bit rate of a transmission channel from the encoder to a decoder and picture_rate is a display rate of pictures.
13. The method as defined in claim 12 , wherein the factor is a factor α, where α comprises:
α
=
1
+
V
status
-
V
target
V
high
-
V
low
,
where V status is the occupancy status, V target is a desired occupancy level of the buffer model, V high and V low are high and low occupancy levels of the buffer model, respectively.
14. The method as defined in claim 13 , where V target is about ⅞ of a capacity of the buffer model, where V high is about 63/64 of the capacity of the buffer model, and where V low is about ⅜ of the capacity of the buffer model.
15. The method as defined in claim 12 , wherein the targeted bit allocation T adaptively varies such that over time, the buffer occupancy level of the buffer model trends to the desired buffer occupancy level.
16. The method as defined in claim 12 , where the desired buffer occupancy level is configured by a user.
17. The method as defined in claim 12 , wherein the buffer model is a virtual buffer verifier (VBV) buffer model.
18. The method as defined in claim 12 , wherein the video encoding process is performed in real time, and where a constant bit rate is used to update a calculation of the buffer occupancy level.
19. The method as defined in claim 12 , further comprising bounding the targeted bit allocation T to a maximum value of T max , where T max comprises:
T max =V status −V low ,
where V status is the occupancy status and V low is a low occupancy level of the buffer model.
20. The method as defined in claim 19 , wherein V low is about ⅜ of a capacity of the buffer model.
21. The method as defined in claim 12 , where V high is about 63/64 of a capacity of the buffer model.