Digital Signal Processing Reference
In-Depth Information
a CPU which could meet the real-time and HD processing requirement is often very
high. In contrast, hardware-based coding process, which means that the processing is
conducted by a specific application specific integrated circuit (ASIC), takes the fol-
lowing advantages. Firstly, it could easily provide video processing performance with
a HD resolution and low time delay; secondly, a hardware-based video encoding
process could be almost finished independently on the ASIC, which would seldom
influence the performance of CPU; thirdly, the cost is more reasonable compared with
that of a high-performance CPU.
Accordingly, hardware-based encoding is chosen for the proposed subsystem. A
specific H.264 encoding chip is chosen, and performs the data stream encoding tasks
on the portable board. Tests shows that system designing in this way could process
HD video and other physiological data simultaneously in real time. As for decoding
on the software-embedded subsystem, an ActiveX+Directshow solution is designed
for the platform. It is easy and convenient to develop a multi-thread and multimedia
program including video displaying, voice processing and data analysis in the form of
an ActiveX plug-in application. However, there is no H.264 decoding filter available
in Directshow toolboxes. So a H.264 decoding project is needed for video displaying
on the clients' device.
CoreAVC decoder is an open-source and free video compression project with low
development complexity. Compared with other projects such as JM86, x264 and
FFmpeg, its fast decoding speed, which is the key point for our decoding design,
could meet our system performance requirement. To sum up, CoreAVC is finally
chosen to be integrated with Directshow for video decoding and displaying on the
software-embedded subsystem.
4.2
V2IP Communication in Wearable Subsystem
The SIP protocol [9] is an Application Layer protocol designed to be independent of
the underlying Transport Layer; it can run on Transmission Control Protocol (TCP),
User Datagram Protocol (UDP), or Stream Control Transmission Protocol (SCTP). It
is a text-based protocol, incorporating many elements of the Hypertext Transfer Pro-
tocol (HTTP) and the Simple Mail Transfer Protocol (SMTP).The main thread of the
Android-based V2IP application is shown in Fig.3. Once an SIP listening thread is
created, it would first check the state of registration to SIP server, and then launch or
receive the session data to update the corresponding android activity, which includes
the video frame and audio data reading and playing.
Fig. 3.
Main thread of Android-based V2IP application
