Image Processing Reference
In-Depth Information
this kind of task. The vector processing in a G5 does particularly well at this kind of com-
putation. Hardware-based encoders are available from companies such as Envivio or
Regardless of whether you use a hardware or software solution to code your video,
the processing creates the same sort of content. You get a sequence of packets containing
fragments of video. Each one may just be a single tile in a mosaic that has to be assembled
to reconstruct the raster.
Comparing Hardware and Software Performance
MPEG-2 hardware coders are very mature these days. The algorithm is well understood and
specialized chip sets are manufactured and assembled into compact, rack-mounted systems.
Video can be encoded between two and four times as fast as real time when processing
cached material, and the hardware is easily able to cope with high-quality live encoding.
Software coders offer more flexibility for tailoring and customization. They run in
general-purpose hardware (e.g., a desktop CPU) so they are slower than the hardware
solutions. Moore's law takes care of this and as computers get faster, so do the coders.
A hardware solution does not have as much opportunity to get faster since it cannot be
upgraded as easily. Moving your software encoder to a faster CPU will yield immediate
performance improvements.
The content will affect the compression speed on a software system. Hardware sys-
tems compress in real time, although they may allow for multiple simultaneous compres-
sion jobs if you buy a large enough system. Codec implementations vary widely and the
computing platform will also make a difference. Your choice of codec implementation will
also have an impact on the measured timings.
The following are some ball-park figures based on some compression runs with
looped test footage of a waterfall.
I selected an MPEG-2 codec and compressed from DV to a standard that is roughly
equivalent to what would go onto a DVD. The results are shown in Table 8-2. I have
assumed that the hardware will compress in real time, so the values in that row of the table
also indicate the clip duration.
The simple rule of thumb is that hardware encoding is generally faster than the soft-
ware alternative because of the multiple parallel processing. Software encoding is cheaper
to buy and works better if you are just processing one job at a time. Hardware comes into
its own when you are compressing two or more live streams at once.
Table 8-2 Your Mileage May Vary
250 Kb file
3 GB file
1.25 minutes
15 minutes
Software on slow PC
2 minutes
29 minutes
Software on average PC
1.4 minutes
20 minutes
Software on fast PC
45 seconds
10 minutes
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