MPEG-2/H.264 transcoding with vector conversion
reducing re-quantization noise
Takeshi Yoshitome, Kazuto Kamikura

Shoji Makino, Nobuhiko Kitawaki

NTT Cyber Space Laboratories
NTT Corporation
Yokosuka, Japan, 239–0847
Email: yoshitome.takeshi@lab.ntt.co.jp

Graduate School of Systems and Information Engineering
University of Tsukuba
Tsukuba, Japan, 305–8573

Abstract—We propose an MPEG-2 to H.264 transcoding
method for interlace streams intermingled with frame and field
macroblocks. This method uses the encoding information froman MPEG-2 stream and keeps as many DCT coefficients of
the original MPEG-2 bitstream as possible. Experimental results
show that the proposed method improves PSNR by about 0.190.31 dB compared with a conventional method.

I. I NTRODUCTION

Input MB

Enc1

D

a

b

c

d

47 31

C’ D’
25 18
DCT
(frame)
(
a’ b’

ME
(mv1)

Enc2

c’ d’

4

3

2
Q
=10)

1

4

3

2

1

40 30
20 10

DCT
a’ b’
40 30
(frame)
(
c’ d’
20 10

VLC
Bit
stream#1
VLD

Almost same

Q
4
=10)
2

3

VLC

1
Bit
stream
#2

Dec2

a

b

a’ b’

40 30

4

3

c

d

c’ d’

20 10

2

1

VLD

No quantization noise
ME
(mv2)

Enc3

DCT
p’ q’
37 32
(field)
(
r’ s’
14
4

Q
3
=10)
1

3

VLC

0
Bit
stream#3

II. N OISE REDUCTION MECHANISM USING FIRST

Dec3

p

q

p’ q’

30 30

3

3

r

s

r’ s’

10

1

0

ENCODING INFORMATION

Data flow examples of transcoding with and without first
MPEG-2 encoding information are shown in Fig. 1. The
data flow of Enc1→Dec1→Enc2→Dec2 is with encoding

A’ B’
ME
(mv1)

re-useBC

re-useDec1

AQuantized
DCT
coefficient

MC-prediction
DCT
Error
coefficient

re-useRecently, it has become important to re-compress MPEG-2
video content to decrease its bitstream size by using a highperformance encoding tool such as H.264. In this decade, anumber of video transcoding studies have been reported [5]–[7] that aim to reduce the H.264 encoding time, which isseveral times larger than that of MPEG-2. However, the image
quality obtained with these approaches becomes lower thanthat of conventional approaches using a directly connected
MPEG-2 decoder and H.264 encoder.
We have focused on the fact that all decisions of thefirst encoding procedure are repeated during the transcoding
procedure to reduce re-quantization noise [1], where ”alldecisions” means decisions on picture type, macroblock type,
motion vectors, DCT type, and so on. This noise suppression
mechanism is effective when the compression standards of thefirst and second encoding are identical, such as for MPEG2/MPEG-2 or H.264/H.264 conversion. We have tried to
expand this approach to apply it to MPEG-2/H.264 transcoding
for intra bit-streams [2], [4]. This paper reports our attempt
to apply this noise suppression mechanism to inter bit-streams
consisting of frame and field macroblocks. First, we discuss
the noise suppression mechanism for progressive bit-streams.
Next, we show the differences between the MPEG-2 andH.264 standards for frame and field macroblocks, analyze how
they affect the noise reduction, and propose an MPEG-2/H.264
transcoding method. Finally, we describe simulation results weobtained and compare the transcoding noises generated by our
method and a conventional method.

information, and that of Enc1→Dec1→Enc3→Dec3 is without
it. For simplicity, the macro-block (MB) size is 2x2. In the first
MPEG-2 encoding, an input MB that includes the pixel values(A, B, C, and D) is processed by motion compensation andorthogonal transformation. Then, the transformed DCT coefficients (47, 31, 25, and 18) are quantized by a quantization
step Δ=10. The quantized DCT coefficients (4, 3, 2, and 1)
are converted to bitstream#1 by variable length coding (VLC).
The quantization from (47, 31, 25, and 18) to (4, 3, 2, and 1)
adds quantization noise so that the decoded MB pixels (a, b,
c, and d) differ from the input MB pixels (A, B, C, and D).
Until this point, transcoding both with and without encoding
information does the same work.
In the transcoding without encoding information, Enc3
searches the best motion vector to minimize motion estimation
error (p’, q’, r’, and s’). If the motion search performance of
Enc3 is higher than that of Enc1, Enc3 can reduce its motion
estimation error (p’, q’, r’, and s’) compared with Enc1’s
motion estimation error (A’, B’, C’, and D’). In the sameway, if the orthogonal transformation performance of Enc3
is higher than that of Enc1, Enc3 can reduce the size of bit-

0

VLD

Quantization noise
Transcoding with Enc1’s info. : Enc1+Dec1 + Enc2+Enc2
Transcoding without Enc1’s info. : Enc1+Dec1 + Enc3+Dec3

Fig. 1.

Transcoding with and without first MPEG-2 encoding information

978-1-4244-7116-4/10/$26.00 ©2010 IEEE

stream#3 compared with that of bitstream#1. However, the requantization noise occurs when DCT coefficients (37, 32, 14,
and 4) are quantized to (3, 3, 1, and 0). In short, Enc3 adds requantization noise even if the bitstream becomes smaller. On
the other hand, in the transcoding with encoding information,
every type of encoding information, such as MB type, motion
vector, DCT mode, and quantization step, is re-used in Enc2.
This re-use of encoding information does not produce any
significant difference between motion compensation errors of
the first encoding and those of the second encoding, nor does it
produce any notable difference between the DCT coefficientsof the two encodings. This means that the re-quantizationnoise added in the second encoding phase is almost zero. As
a result, the same motion estimation error and the same DCT
quantization coefficients are obtained. Unfortunately, there isno bit reduction because the sizes of bitstream#1 and #2 arealmost the same when these encodings make use of the same
compression tool. But transcoding using different compression
tools, such as MPEG-2 to H.264 transcoding, may reduce thebitstream size because the performance of H.264’s entropy
coding (CABAC) is higher than that of MPEG-2’s entropy
coding (VLC).

TABLE IM AJOR DIFFERENCES BETWEEN MPEG-2 AND H.264

MPEG-2

H.264

H.264
re-enact

yes

4x4, 4x8,
8x4, 8x8
8x16,16x8
16x16
0.25pix
integerDCT
8x8(*1)4x4
yes(*1)

no

no

OK

yes

no

?
checked?

Block size

16x16

Vector resolution
Orthogonaltransformation
Size of orthogonaltransformation
Specification ofquantization matrix
Deadzone in intra
quantization
Deadzone in interquantization
MC specification unitof field/frameMB
DCT specification unitof field/frameMB

0.5pix
DCT
8x8

each
MB
each
MB

OK
OK
?
checked
OK
OK

pair
MBs
pair
?
MBs
(*1): only High-Profile

III. D IFFERENCES BETWEEN MPEG-2 AND H.264

IV. F RAME /F IELD MACROBLOCK SPECIFICATION

DCT of MPEG-2
Input Image

1
2
3
4
5

16 pixcel

(a)

15
16

Frame MB

A

B

1
2

Field MB

C

D

15
16

1
3

a

b

c

d 4

8
9

15
2

16

16 pixcel

Integer DCT of H.264
Input Image

16 pixcel

1
2
3
4
5
15
16
17
18
19
20
21

(b)

16 pixcel

As depicted in Fig. 1, there is a close resemblance between
the decoded images of the first and second decoders when
the compression standards of the first and second encodings
are exactly the same. To re-enact the effect of this noise
reduction mechanism, we must control H.264 behavior toimitate MPEG-2 behavior as much as possible when the firstencoder is MPEG-2 and the second encoder is H.264. The
two encoders are similar but are not upper compatible. The
differences between them are listed in Table I. The ”ok” meansthat H.264 can recreate the same MPEG-2 function in thetable. The ”?” means that H.264 can process the function
only in a similar but not identical way that MPEG-2 does.
The ”checked” means that these differences were analyzed in
our previous work [2], [3]. The following two functions are
not exactly the same between MPEG-2 and H.264, and are notinvestigated: (1) Specification unit of DCT type representing
frame MB or field MB, (2) Specification unit of motion
compensation type representing frame MB or field MB. In
the next section, we describe these differences in detail andshow a way to overcome them.

31
32

Frame pair MB

A

B

1
2

Field pair MB

a

b

e

f

8
9

C

E

D

F

15
16

17
18

H

31
32

15
17
19
31

2

c

d 4

g

h 20

24
25

G

1
3

16
18

32

16 pixcel

8x8 DCT block

Fig. 2.

DCT type specification in MPEG-2 and H.264

A. DCT type specification in MPEG-2 and H.264
The DCT type specification of MB in MPEG-2 and H.264
is shown in Fig. 2. Although a DCT type can be specified foreach MB independently in MPEG-2, H.264 specifies the DCT
type for each pair of MBs that adjoin each other above andbelow. When an upper MB is specified as the frame DCT and
its lower MB is specified as the field DCT in MPEG-2, theDCT type of one MB is different from its DCT type specified
in H.264, whether the DCT type of the pair of MBs is frameor field type in H.264.

In our previous trial [4], we compared the two methods
that select frame MB pairs or field MB pairs when DCT
types of upper and lower MB were different in MPEG-2. The
simulation results obtained show that the selection of frame
MB pairs is superior to that of field MB pairs in PSNR. In
this paper, we use this MB pair selection method again for
intra MBs, as shown in Table II.

TABLE IIR ELATIONSHIP BETWEEN H.264 MB PAIR TYPE AND MPEG-2 DCT TYPE

Motion compensation of MPEG-2

Input Image

Frame MB

SUCCESSION

(a)

1
2
3
4
5

16 pixcel

Input
Output H.264
MPEG-2
Frame
Field
DCT
pair MB
pair MBtype
selection
selection
upper
lower
upper lower upper lower
MB
MB
MB
MB
MB
MB
Frame Frame
O
O
X
X
Field
O
X
X
O
Field
Frame
X
O
O
X
Field
X
X
O
O
O: Succession, X: No succession

Ourselection
type
Frame
Frame
Frame
Field

Field MB

1
2
8
9

15
16

1
3
15
2
4

MV
MPEG

15
16

MPEG

Field vector

Motion compensation of H.264
Input Image

Frame pair MB

Field pair MB

1
2

The relationship between the pixel group and the motion
vector in MPEG-2’s MB is shown in Fig. 3. A single frame
motion vector M VM P EG represents the motion of the MB
including 16x16 pixels when its motion type is specified asframe. When its motion type is specified as field, a top fieldmotion vector mvtM P EG represents the motion of 16x8 pixels
included in the top field MB; a bottom field motion vector
mvbM P EG represents the motion of 16x8 pixels included in
the bottom field MB. H.264 specifies the motion type for eachpair of MBs that adjoin each other above and below. Whenthe MB pair is specified as a frame, a frame vector M V 0H264
represents the motion of the above MB, and another frame
vector M V 1H264 represents the motion of the below MB.
When the MB pair is specified as a field, the four motion
vectors mvt0H264 , mvt1H264 , mvb0H264 , and mvb1H264 areused. The vectors mvt0H264 and mvb0H264 represent the
motion of top and bottom field pixels in the upper MB. The
vectors mvt1H264 and mvb1H264 represent the motion of top
and bottom field pixels in the lower MB. This is similar to a
DCT type specification in which H.264 specifies the motion
type for each pair of MBs that adjoin each other above andbelow. The MPEG-2 motion type succeeds to H.264 only whenboth the upper and lower MBs have the same motion type in
MPEG-2.

16 pixcel

(b)

1
2
3
4
5

8
9

1
3
15
17
19

MV0

H264

15
16

15
16
17
18
19
20
21

16 pixcel

B. Motion compensation type specification in MPEG-2 and
H.264

MPEG

mvb

16

Frame vector

16 pixcel

mvt

24
25

H264

2
4

Fig. 3.

mv0b

H264

MV1
H264

16
18
20

31
32

16 pixcel

H264

mv1t

31

17
18

31
32

mv0t

mv1b

H264

32

Frame vector

Field vector

Motion compensation type specification in MPEG-2 and H.264

Converted
Converted
TopField Vector
BottomField Vector(reference=TopField) (reference=BottomField)

Original
Frame Vector

MV0= -2

mvt= -20

mvb= -2
0

(a)
2

2

4

4

Top Field Pixel

Original
Frame Vector

0

2

2

4

4

Bottom Field Pixel

Converted
Converted
TopField Vector
BottomField Vector(reference=BottomField) (reference=TopField)

MV0= -1(b)0mvt= -2

mvb= 0
0

0

2

2

4

4

0

0

2

2

4
Top Field Pixel

4
Bottom Field Pixel

Fig. 4. Conversion from frame vector to field vector(a)Y vector= –2 pix, (b)Y vector = –1 pix

C. Conversion method from frame vector to field vector
We introduce a method of converting from frame vector
to field vector to increase the number of H.264 MBs thatsucceed to the MPEG-2 motion type. Figure 4shows examples
of conversion from frame vectors to field vectors. Figure 4(a)shows the conversion when the vertical vector value equals −2
pixels and Fig. 4(b) shows it when the value equals −1 pixels.
In Fig. 4(a), the top field vector points to the top field pixels in
the reference picture, and the bottom field vector points to thebottom field pixels. In contrast, in Fig. 4(b), the top field vector
points to the bottom field pixels, and the bottom field vector
points to the top field pixels. The top field pixels are locatedone pixel position higher than that of bottom field pixels.
Therefore, a frame vector that indicates −1 pixel movement is
replaced by a top field vector that indicates −2 movement anda bottom field vector that indicates zero movement. The rules

for converting a frame vector to two field vectors are shownin the following equations.
mvt0x = M V 0x
mvt0y = M V 0y + α−1 (M V 0y = ±1, ±3, ±5, ..)where α =0 (M V 0y = otherwise)
mvb0x = M V 0x
mvb0y = M V 0y + β+1 (M V 0y = ±1, ±3, ±5, ..)where β =0 (M V 0y = otherwise)

(1)

(2)


t0ref =

bottom (M V 0y = ±1, ±3, ±5, ..)top(M V 0y = otherwise)top(M V 0y = ±1, ±3, ±5, ..)b0ref =
bottom (M V 0y = otherwise)(3)

hardware encoders, as shown in Table IV. The succeeding ratio
is 57.2% without vector conversion and increases to 72.1%
using vector conversion.

(4)

A. Proposed Method

V. P ROPOSED M ETHOD AND E VALUATIONIn these equations, the MPEG-2 frame vector is M V 0
and its X and Y direction values are M V 0x and M V 0y.
The H.264 top and bottom field vectors for the upper MB
are mvt0 and mvb0. Their X and Y direction values are
mvt0x, mvt0y, mvb0x and mvb0y. The reference fields of
mvt0 and mvb0 are t0ref and b0ref . These conversions
are only approximations, but are sufficiently accurate thatthe noise reduction effect mentioned in section II remains
when using them. The relationship between noise reduction
effect and the vector conversion will be described in Section
V-C. Table III shows the succession of DCT and motion
compensation from MPEG-2 to H.264 using frame to field
vector conversion. There are 16 cases of the combinationof DCT type and motion compensation type for a MB pair in
MPEG-2. The right side of the table shows whether the H.264
MB succeeds or does not succeed to the DCT type and the
motion compensation type in frame pair selection or in field
pair selection. An “o” means that H.264 MB succeeds without
vector conversion. A “#” means that H.264 MB succeeds with
vector conversion. An “x” means that H.264 MB does not
succeed. We measured the DCT type and motion compensation
type of MPEG-2 bitsteams generated by five commercial
TABLE IIIT HE RELATIONSHIP BETWEEN THE SUCCESSION OF DCT AND MOTIONCOMPENSATION FROM MPEG-2 TO H.264 AND THE PAIR TYPE
SELECTION IN H.264.
Input MPEG-2
Output H.264
DCT
Motion
Frame
Field
type
compensation
pair MB
pair MBtype
selection
selection
up
low
up
low
up
low
up
low
MB
MB
MB
MB
MB
MB
MB
MB
0
Fr
Fr
o
o
x
x
1
Fr
Fi
o
x
x
x
2
Fi
Fr
x
o
x
x
3
Fr
Fi
x
x
x
x
4
Fr
Fr
o
x
x
#
5
Fi
Fi
o
x
x
o
6
Fi
Fr
x
x
x
#
7
Fi
x
x
x
o
8
Fr
Fr
x
o
#
x
9
Fr
Fi
x
x
#
x
10
Fi
Fr
x
o
o
x
11
Fi
Fi
x
x
o
x
12
Fr
Fr
x
x
#
#
13
Fi
Fi
x
x
#
o
14
Fi
Fr
x
x
o
#
15
Fi
x
x
o
o
Number of succeeded MB
448(4) 8(4)Fr: Frame, Fi: Fieldo: Succeeded MB without vector conversion#: Succeeded MB with vector conversion
x: Non-succeeded MB( ): Number of succeeded MBs without vector conversion
Group
No.

The inter-MB conversion rule of the proposed method for
P-pictures is shown in Table.V. Our method uses the intraMB conversion rule that has already been reported in [4]. For
B-pictures, our method uses a conventional method that does
not use first encoding information.
The method selects pairs of MB type, MB type, motion
vector, and T ransf orm size 8x8 f lag according to theinformation of the DCT type and the motion compensation
type in MPEG-2. The MB pair type selection of H.264 is set
up to maximize the number of MBs that succeed to the DCT
type and motion compensation type from MPEG-2 to H.264.
The method does not select whether to use vector conversion
when the number of MBs succeeding MPEG-2’s type does
not change whether or not vector conversion is used. Thisis because the conversion from a single frame vector to two
field vectors increases the bitstream size. For example, when
the group number is four in TableIII, a single MB succeeds
the MPEG-2’s type whether or not vector conversion is used.
TableV shows that our method selects a frame pair that does
not require the conversion in such cases.
For succeeding MBs, the MB type is P L0 16x16 inframe pair selection, or P L0 L0 16x8 in field pair selection.
The motion vectors are succeeded directly, or converted by
the vector conversion mentioned in SectionIV-C. There isno need to search a motion vector that requires a large
CPU time. The T ransf orm size 8x8 f lag is set to one
to equalize the DCT size in H.264 and MPEG-2. The quantization step is selected to be the value nearest to that of
MPEG-2’s quantization step. For non-succeeding MBs, theMB type, T ransf orm size 8x8 f lag, and motion vectors
are re-judged or re-searched using the same way that theconventional method does.
The following common settings are declared in the H.264’s
picture header or slice header. The H.264 profile is a highprofile one that makes it possible to use the same size of
MPEG-2 DCT. The coefficient of the H.264 quantization
matrix is set to the same as that of the MPEG-2’s matrix.
Because the H.264 encoder can refer to the same picture
TABLE IV
T HE POSSIBLE SUCCEEDING RATIO OF BOTH DCT TYPE AND MOTIONCOMPENSATION TYPE FROM MPEG-2 TO H.264 MEASURED IN FIVECOMMERCIAL MPEG-2 ENCODER (%)

Encoder A
Encoder B
Encoder C
Encoder D
Encoder E
Ave.

Without
vector conv.
53.9
45.3
59.4
64.8
62.6
57.2

With
vector conv.
78.4
77.8
65.6
70.5
68.0
72.1

Difference
22.4
32.5
6.2
5.7
5.4
14.9

TABLE VI NTER MB CONVERSION RULE FROM MPEG-2 TO H.264 IN P- PICTURE
Input MPEG-2
Output H.264
Motion comp.
Group
DCT typetypePair
MB type
Vector
no.
up
low
up
low
MB
up
low
up
low
MB
MB
MB
MB
type
MB
MB
MB
MB
0
Fr
Fr
Fr
P L0 16x16
P L0 16x16
succession
succession
1
Fr
Fi
Fr
P L0 16x16
re-judge
succession
re-search
2
Fi
Fr
Fr
re-judge
P L0 16x16
re-search
succession
3
FrFi
re-judge
re-judge
re-judge
re-searchre-search
4
Fr
Fr
Fr
P L0 16x16
re-judge
succession
re-search
5
Fi
Fi
Fr
P L0 16x16
re-judge
succession
re-search
6
Fi
Fr
Fi
re-judge
P L0 L0 16x8
re-search
conversion
7
FiFi
re-judge
P L0 L0 16x8
re-search
succession
8
Fr
Fr
Fr
re-judge
P L0 16x16
re-search
succession
9
Fr
Fi
Fi
P L0 L0 16x8
re-judge
conversion
re-search
10
Fi
Fr
Fr
re-judge
P L0 16x16
re-search
succession
11
Fi
Fi
Fi
P L0 L0 16x8
re-judge
succession
re-search
12
Fr
Fr
Fi
P L0 L0 16x8 P L0 L0 16x8 conversion conversion
13
Fi
Fi
Fi
P L0 L0 16x8 P L0 L0 16x8 conversion
succession
14
Fi
Fr
Fi
P L0 L0 16x8 P L0 L0 16x8
succession
conversion
15
Fi
Fi
P L0 L0 16x8 P L0 L0 16x8
succession
succession
Fr: frame, Fi: field, conversion: convert from frame vector to field vector

TABLE VI
S UCCESSION MANNER AND PSNR IMPROVEMENT OF THE FIRST
P- PICTURE USING PROPOSED METHOD

to which the MPEG-2 encoder refers, the reference picture
number is one for P-pictures and two for B-pictures.
B. Simulation conditions
The interlace video sequences, which size is 720 x 480
pixcels, were compressed first by MPEG-2 encoder (TM5 [8])to generate bitstreams to input the proposed and conventionaltranscoder. We used an original jm12.1 [9] program for theconventional transcoding. It does not use the encoding information except picture type, and does an ordinary motion search
and a MB type selection. The conventional transcoding had
no restrictions with regard to selecting MB type and motion
vector type, so its output bit-streams included the all-MB
mode and all motion type, and also included all available DCT
sizes. We used the modified jm12.1, which can input the firstencoding information, for our proposed transcoding method.
The quantization step Δ was fixed. The frame rate is 30 fps.
The GOP size is 15 and its structure is IBBP(M=3, N=15)
for the simulations of both the conventional and proposed
methods.
C. Noise reduction generated by the type succession
Using the video sequence ”Cheerleader”, we measured thefirst P-picture’s PSNRs of our method and a conventional
method through simulation. Every MB of our method wasclassified by the combination of their DCT type and motion
compensation type in MPEG-2. Each MB compressed with
our method was compared to the MBs compressed by theconventional method located on the same image position. The
relationship between the MB group and the PSNR is shown in
Table VI. The meanings of MB group having “o”, “#”, and”x” are the same as in Table III. In the “o” MB group, which
succeeds the MPEG-2’s DCT and motion compensation types
without vector conversion, the PSNR of the proposed method
is 0.67–2.04 dB higher than that of the conventional method.
In the “#” MB group, which succeeds these types with vector

T ransf orm size
8x8 f lag
up
low
MB
MB
1
1
1
re-judge
re-judge1
re-judge re-judge
1
re-judge1
re-judge
re-judge1
re-judge1
re-judge
1
1
re-judge
re-judge
1
1
re-judge
1
1
1
1
1
1
1
1

G
r
o
u
p
#
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Proposed
Conventional
Succession
PSNR
PSNR
manner
(dB)
(dB)
up
low
up
low
up
low
MB MB
MB
MB
MB
MB
(1)
(2)
(3)
(4)
98
o
o
43.02 43.00 41.51 41.54
41ox
40.22 38.04 38.22 37.94
53xo
37.62 40.13 37.44 38.16
79xx
37.65 37.72 37.69 37.67
57ox
41.33 39.92 39.28 40.47
34ox
40.62 38.24 39.42 38.50
12x#
38.38 41.66 38.46 40.40
39xo
37.49 38.61 37.58 37.86
31xo
39.95 40.72 39.94 38.76
8#
x
39.27 37.71 39.05 37.70
33xo
38.36 40.50 38.43 39.25
36ox
38.66 37.69 37.98 37.69
60##
41.26 41.60 40.21 40.08
19#o
40.89 40.27 39.88 39.11
14o#
40.76 40.99 38.88 39.77
61oo
39.15 39.69 38.04 38.22
o: succeeded without vector conversion#: succeeded with vector conversion
x: non-succeeded
Num
of
pair
MB

Difference
PSNR
(dB)
up
low
MB
MB
(1-3)
(2-4)
1.51
1.45
1.99
0.09
0.18
1.97
-0.03
0.05
2.04
-0.54
1.19
-0.25
-0.08
1.26
-0.08
0.75
0.01
1.96
0.21
0.00
-0.07
1.25
0.67
-0.00
1.04
1.51
1.01
1.16
1.87
1.22
1.11
1.47

conversion, the PSNR of the proposed method is also 0.21–
1.51 dB higher. However, the PSNR difference is less than 0.18
dB in the “x” MB group in which there is no succession. These
results indicate that transcoding noise is reduced in succeeding
MBs whether or not the vector conversion is used.
D. Proposes method and distance from I-pictures
The relationship between the distance from an I-picture
and the PSNR of a P-picture is shown in Table VII. The
conventional PSNR column and the PSNR difference column
are the interpolation values when the conventional method
generates the same bitstream in terms of size. These inter-

TABLE VII
D ISTANCE FROM I- PICTURES AND PSNR OF P- PICTURES

Seq.
Boat

Bus

Cheer
Leader
Plane

Race

Susie

Input
Proposed
MPEG-2
methodDist. PSNR Picture Picture Comp PSNR
(dB)
bits(k) bits(k) ratio.
(dB)
336.69 122.8 102.0 0.83
35.75
636.40 130.7 112.7 0.86
35.19
936.30 132.7 112.7 0.85
34.92
1236.19 140.1 122.1 0.87
34.64
334.01 213.8 185.9 0.87
32.80
634.07 219.2 193.9 0.88
32.39
934.08 223.2 203.6 0.91
32.14
1234.05 208.1 198.8 0.96
31.97
334.14 373.8 346.9 0.93
32.31
634.10 338.2 314.2 0.93
32.10
934.09 348.9 320.1 0.92
32.01
12
34.11 351.4 328.0 0.93
31.91
337.82 80.2
68.5
0.85
36.82
6
37.70 80.3
70.8
0.88
36.32
9
37.63 88.3
82.1
0.93
35.96
12
37.26 103.2 94.1
0.91
35.58
3
35.07 105.2 81.4
0.77
34.30
6
35.21 105.0 82.5
0.79
34.24
9
35.09 119.0 98.2
0.83
33.89
12
35.20 129.5 115.0 0.89
33.70
337.56 51.0
27.7
0.54
36.80
6
37.56 46.5
23.5
0.51
36.55
9
37.58 44.0
23.1
0.53
36.35
12
37.43 55.7
34.2
0.61
35.98

Conventional
methodPSNR Diff.
(dB)
(dB)
35.29 0.46
35.11 0.08
34.90 0.01
34.79 -0.15
29.84 2.95
30.09 2.29
30.29 1.85
30.06 1.91
31.88 0.43
31.82 0.28
31.91 0.09
31.87 0.03
36.05 0.77
35.93 0.40
35.97 -0.01
35.85 -0.27
33.98 0.32
34.20 0.04
34.06 -0.17
34.12 -0.43
36.39 0.40
36.43 0.11
36.31 0.04
36.06 -0.07

polation values are calculated using the simulation results ofthe conventional method. The decrease in PSNR difference
between the proposed method and the conventional method isabout 0.32-2.95 dB for the first P-picture when the distanceis equal to three. This indicates that the proposed method issuperior to the conventional method for the P-pictures thatare located near I-pictures. The average PSNR improvementof the proposed method is (0.86 dB, 0.53 dB, 0.30 dB, and0.17 dB) when the distances are (3, 6, 9, and 12) for six
video sequences. Although the effect of the proposed method
becomes smaller as the distance between I-picture and Ppicture becomes larger, the PSNR of the proposed method
is higher than that of the conventional method.
E. PSNR comparison at the same bitrate
The PSNRs of the conventional method and the proposed
method are listed in Tables VIII and IX. The quantization
step was set to 8 in Table VIII and to 16 in Table IX. The
conventional PSNR column is the interpolation value when theconventional method generates the same bitrate. However, the
PSNR of the proposed method is slightly lower than that of
the conventional method only for the “Race” in Table VIII;
the remaining nine simulation results show that the PSNR of
the proposed method is higher than that of the conventional
method. In other words, the PSNR improvement is 0.19 – 0.31
dB. These results indicate that the proposed method is superior
to the conventional method.
VI. C ONCLUSION
We proposed a MPEG-2 to H.264 transcoding method
for interlace bit-streams intermingled with frame and field
macroblocks. This method uses encoding information fromTABLE VIIIC OMPRESSION RATIO AND PSNR OF PROPOSED METHOD(Q UANTIZATION S TEP =8)

Seq.
Boat
Bus
Cheer
Plane
Race
Susie
ave.

Input
MPEG-2PSNR Bitrate(dB)(kbps)
39.21 3279.9
37.96 4796.0
37.89 7128.6
40.43 2339.6
38.46 3419.5
40.17 1555.7
39.02 3753.2

ProposedmethodBitrateComp(kbps)
ratio.
2536.30.77
4077.20.85
6146.90.86
1789.50.76
2653.1
0.78
936.8
0.60
3023.3
0.77

PSNR
(dB)
38.02
36.36
36.06
39.21
37.01
39.10
37.63

Conventional
methodPSNR Diff.
(dB)
(dB)
38.00 0.02
35.48 0.88
35.98 0.08
39.19 0.02
37.04 -0.03
38.97 0.13
37.44 0.19

TABLE IXC OMPRESSION RATIO AND PSNR OF PROPOSED METHOD(Q UANTIZATION S TEP =16)

Seq.
Boat
Bus
Cheer
Plane
Race
Susie
ave.

Input
MPEG-2PSNR Bitrate(dB)(kbps)
35.90 1666.2
33.54 2315.0
33.23 3423.2
37.25 1307.2
34.69 1421.7
37.76 898.7
35.40 1838.7

ProposedmethodBitrateComp.
(kbps)
ratio
1080.90.65
1805.70.78
2934.3
0.86
821.5
0.63
854.9
0.60
363.0
0.40
1310.1
0.65

PSNR
(dB)
34.54
31.98
31.57
35.92
33.57
36.69
34.05

Conventional
methodPSNR Diff.
(dB)
(dB)
34.49 0.05
30.74 1.24
31.39 0.18
35.81 0.11
33.54 0.03
36.50 0.18
33.74 0.31

MPEG-2 streams and keeps as many DCT coefficients of
the original MPEG-2 bitstream as possible. The frame tofield vector conversion increases the amount of MPEG-2
information succeeding MBs, which makes it possible toreduce re-quantization noise. Experimental results show thatthe proposed method improves PSNR by about 0.19-0.31 dB
compared with a conventional method. The advantage of the
proposed method is not only high transcoded video quality but
also reduced CPU time in searching motion vectors.
R EFERENCES[1] P. Guilotel, et al ”Adaptive Encoders: The New Generation of MPEG-2
Encoders” SMPTE journal (April 2000)[2] T. Yoshitome, et al ”A study of MPEG-2 to H.264 Intra Transcoding for Progressive Contents” ITE Journal, 62,11,pp1819-1824,2008 (inJapanese)[3] T. Yoshitome, et al ”An MPEG-2 to H.264 Transcoding Method Preserving DCT Information for Progressive Contents” ITE Journal, 63,6,pp837846,2009 (in Japanese)[4] Takeshi Yoshitome, et al ”A Re-quantization Noise Reduction Method in
MPEG-2 to H.264 Intra Transcoding”, IEEE Symposium on Industrial
Electronics and Application (ISIEA 2009), Kuala Lumpur, Malaysia,
pp.94-99, Oct 4-6, 2009
[5] Xiaoan Lu, et. al ”Fast mode decision and motion estimation for H.264
with a focus on MPEG-2/H.264 transcoding” in Proc. of ISCAS 2005,
23-26 May 2005, pp1246-1249 Vol.2[6] Gao Chen, et al ”Efficient block size selection for MPEG-2 to H.264
transcoding” Proc. of the 12th annual ACM international conference on
Multimedia[7] Joo-Kyong Lee, et al ”Quantization/DCT Conversion Scheme for DCTdomain MPEG-2 to H.264/AVC Transcoding” IEICE Trans. Commun.,E87-B, 7 (July 2004)[8] MPEG-2, Test Model 5 (TM5), Doc ISO/IEC JTC/SC29/WG11/N0400,
Test Model Editing Committe, April 1993.
[9] JointVideo
Team(JCT),“Reference
Software
JM12.1”,
http://iphome.hhi.de/suehring/tml/