Image Processing Reference
not. This is useful on lossy connections because if a sync error happens, the player
can reconstruct its image again when the next key frame arrives. You can determine
the maximum distance according to the service level you want to provide.
Key Frame (Every): Key frames are inserted only at predicted times.
All Key Frames: When very high bit rates are used, you can discard P- and B-
frames and just encode I-frames for transmission. This results in very good pres-
entation quality but is less efficient in terms of compression factors.
Define Any Postprocessing That Is Required
Not a great deal of additional processing is necessary on the final output other than pack-
aging it into the correct kind of file container. You might also set up the destination for the
output-compressed file at this stage.
You could do some hinting on the file if you intend to stream it. This is mandatory
for files that are going to be streamed via the RTSP protocol. Ignore this step if you don't
intend to stream the files.
Another possible postprocess is the embedding of any text tracks, URL tracks, or
other metadata. This must be done after compression. It is better to deliver caption texts
as a separate text stream rather than a burned-in image, as it leads to a cleaner presenta-
tion with no compression artifacts. It is also much more efficient in terms of bit-rate usage.
There is postprocessing that takes place at the client end but this is in the decoder
and happens after the bit stream has been converted back into a pixmap.
Setting Up a Batch-Encode Server
If you are only going to run the occasional encode job, it is not worth the effort of setting
up a batch-encoding process. On the other hand, if you are running a service delivering
encoded video, you want to be able to throw encoding jobs at a farm of encoders without
too much manual effort. In a more extreme situation such as running a major news Web
site where you are creating upwards of 200 five-minute clips every day for a variety of
platforms, a workflow process driving a batch-oriented encoder farm is the only way to
solve the problem.
Products such as the Popwire Compression Engine offer an industrial-strength,
server-based solution. Other possibilities at the high end are solutions by Telestream,
which has a highly engineered batch-transcoding product called Flip Factory. At the lower