Triple-Play Service Deployment

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Chapter 6: Troubleshooting Video in the Headend
Preparing Video for DSL Delivery
While the triple-play service provider does not perform the
original compression (this is carried out by the content provider),
the provider must achieve a more efficient bit rate for those
programs to enable delivery in a DSL network.This is accomplished
either through transrating or by converting the video to an MPEG-
4 AVC format. The conversion can be carried out either by reencoding
(decoding the video back to an uncompressed format,
and then re-encoding it), or transcoding (converting a compressed
MPEG-2 video directly into a compressed MPEG-4 video).
In either case, the operator introduces some risk to the quality of
the video and, as a result, must have the ability to test the new
product to ensure the quality has not been compromised. This is
an important step, as the content providers maintain stringent
quality standards for their programming. Content providers will
not allow an operator to deliver their services if they cannot
guarantee the end product suffers no degradation in quality.
However, it is more of a qualification exercise than operational test
practice. Compression is effectively an isolated, “closed-system”
process with repeatable outcomes for the same input. The
operator can play known good content into the compression
stage and then use an Elementary Stream Analyzer to validate the
output picture quality of the new MPEG-4 video file. Figure 6.3
depicts an analysis screen from an Elementary Stream Analyzer,
segmenting the video frame into macro blocks and showing the
quantization (level of compression) and motion vectors per
macro block.