![](bg5.png)
kbps but different temporal rates. The lecturer was
encoded at 25Hz whereas the whiteboard was
encoded at 6.25Hz. For comparison with the video
frames, after decoding the two objects these were
combined to form frames again.
As we can observe in Figure 7, the proposed
scheme achieves a good performance comparing
with both references. By using different coding
parameters for each video object, the transcoded
pictures have better spatial quality in the whiteboard
area, mainly because of its reduced temporal rate
which allows more bits to encode the texture. The
composition problem that arises when different
video objects are displayed at different frame rates
may be overcome by filling in the missing areas
with pixels from the surrounding area. However,
this issue is not addressed in this paper. The same
behaviour as shown in Figure 7 is obtained for other
transcoding ratios.
5 CONCLUSION
The transcoding scheme proposed in this paper is
suitable for e-learning applications where MPEG-2
to MPEG-4 conversion might be useful. The
experimental results show that a good performance
is achieved by choosing different temporal rates for
video objects according to their specific
characteristics.
A possible application of this type of transcoding is
in wireless access where the user may receive the
audio and only the whiteboard visual information at
much lower bit rates but still with an acceptable
quality of service.
REFERENCES
Assuncao P. and Ghanbari M, 1998. A frequency domain
transcoder for dynamic bit rate reduction MPEG-2 bit
streams, IEEE Transactions on Circuits and Systems
for Video Technology, Vol. 8, No 8, pp. 953-967.
Dorai, C., Oria V. and Neelavalli V., 2003. Structuralizing
Educational Videos Based on Presentation Content,
IEEE International Conference on Image Processing,
Barcelona-Spain.
Guo W., Lin L., Zheng W and Zheng W., 2001.
Mismatched MB Retrieval from MPEG-2 to MPEG-4
Transcoding. IEEE Pacific Rim Conference on
Multimedia, Beijing, China.
ISO/IEC 13818-2, 1995. Generic Coding of Moving
Pictures and Associated Audio - Part 2: Video.
ISO/IEC 14496-2, 1999. Information Technology -
Generic Coding of Audio-Visual Objects – Part 2:
Visual, Vancouver.
Kim M., Choi J. G., Kim D., Lee H., Lee M. H., Ahn C.
and Ho Y-S., 1999. A VOP Generation Tool:
Automatic Segmentation of Moving Objects in Image
Sequences Based on Spatio-Temporal Information,
IEEE Transactions on Circuits and Systems for Video
Technology, pp. 1216-1226, Vol. 9, No 8.
Pereira F., Burnet I., 2003. Universal Multimedia
Experiences for Tomorrow, IEEE Signal Processing
Magazine, vol. 20, No. 2.
Reyes G., Reibman A., Chang S-F., Chuang J., 2000.
Error Resilient Transcoding for Video over Wireless
Channels, IEEE Journal on Selected Areas in
Communications, Vol. 18, No. 6.
Shanableh T., and Ghanbari M., 2000. Heterogeneous
video transcoding to lower spatio-temporal resolutions
and different encoding formats, IEEE Transactions on
Multimedia, Vol. 2, No 2, pp. 101-110.
Takahashi K., Satoh K., Suzuki T., Yagasaki Y., 2001.
Motion Vector Synthesis Algorithm for MPEG2-to-
MPEG4 transcoder, Visual Communications and
Image Processing, Proceedings of SPIE, Vol. 4310,
pp. 872-882.
Xie R., Liu J. and Wang X. 2003. Efficient MPEG-2 to
MPEG-4 Compressed Video Transcoding, Visual
Communications and Image Processing, Proceedings
of SPIE Vol. 4671, pp. 192-201, Lugano-Switzerland.
Xin J., Sun M-T., Choi B-S., Chun K-W., 2002. An
HDTV to SDTV Spatial Transcoder, IEEE
Transactions on Circuits and Systems for Video
Technology, Vol. 12, No 11.
Yin L., Yang R., Gabbouj M., Neuvo Y., 1996. Weighted
Median Filters: A Tutorial, IEEE Trans. on Circuits
and Systems, vol. 43, n 3, pp. 157-192.
Yu X-D., Duan L-Y. and Tian Q., 2003. Robust Moving
Video Object Segmentation in the MPEG Compressed
Domain, IEEE International Conference on Image
Processing, Barcelona-Spain.
ICETE 2004 - WIRELESS COMMUNICATION SYSTEMS AND NETWORKS
282