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gained by using MPEG-2 encoding and mapping
into TS ISO 13818-1. These results confirm with
hard figures the first, general insights gained from
the work described in paper (MacAulay, Felts,
Fisher, 2005), in which encapsulation with Native
RTP was also investigated. Here too, it is clear that
for the codec MPEG-4/AVC it is perfectly adequate
to work with the medium preset. The ultrafast preset
delivers the worst results by far, and its use should
be avoided in practice.
Figure 8: PEVQ values as a function of packet loss for the
MPEG-4/AVC codec with Native RTP, a maximum NAL
unit size of 1400 bytes and a coding rate of 10 Mbps.
The results gained so far in the course of this
study strongly suggest that when the codec MPEG-
4/AVC is used, the size of the NAL unit does indeed
have a significant influence on QoE. So it makes
sense not to use the default mode of the encoder
either when using the MPEG-2 TS for contents
encoded with MPEG-4/AVC. Instead, the NAL unit
size is set to 1400 bytes. All the following analysis
scenarios use this setting. For lack of space no
further figures are given in this paper. The results
obtained here show significantly better QoE values
than those gained using the default setting of the
codec MPEG-4/AVC (cf. Figs 5 and 6). Here again,
the medium preset returns the best QoE values. They
are comparable with the levels of quality attained for
the MPEG-2 codec. In a loss-free environment the
strengths of the MPEG-4/AVC encoder really
become evident. It delivers QoE values approx. 0.5
MOS better than the corresponding values for the
MPEG-2 codec. Quite clearly it is actually possible
to use the MPEG-2 TS to encapsulate MPEG-
4/AVC-encoded content as long as the encoder
settings have been properly adjusted. This is of
immense practical significance.
5 SUMMARY
The focus of this paper has been the subject of
quality of service in the service IPTV. A large-scale
investigation revealed the strengths and weaknesses
of both methods of encapsulating video streams. It
became clear that the ISO/IEC 13818-1-formatted
transport stream is perfectly suitable for the transport
of MPEG-2-encoded video signals. By contrast,
MPEG-4/AVC-encoded video signals (using the
default settings of the encoder) do have considerable
problems with this kind of encapsulation. The study
has shown that in this case it makes sense to work
either with the encapsulation type Native RTP or, in
the case of MPEG-2 TS, to adjust the settings of the
encoder (by limiting the size of the NAL unit).
REFERENCES
ISO/IEC 13818-2, 1995. Information technology --
Generic coding of moving pictures and associated
audio information, http://cutebugs.net/files/mpeg-
drafts/is138182.pdf, page last viewed Mai 2012.
ITU-T H.264, 2007. The Advanced Video Coding
Standard, http://www-ee.uta.edu/Dip/Courses/EE5359
/H.264%20Standard2007.pdf, page last viewed Mai
2012.
ISO/IEC 13818-1, 2000. Generic coding of moving
pictures and associated audio information: Systems,
http://mumudvb.braice.net/mumudrupal/sites/default/fi
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IETF RFC 2250, 1998. RTP Payload Format for
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Company “Opticom”, http://www.opticom.de, page last
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MacAulay, A., Felts, B., Fisher, Y., 2005. IP Streaming of
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