Choosing an appropriate video codec
There are a variety of applications that use codecs - from HDTV broadcast to desktop multimedia applications, Web-based video and multimedia messaging service (MMS) on mobile phones. The specific application determines which codec is most appropriate.
The product developer’s objective is to use the most efficient and elegant codecs for the product. However, it also may become necessary to use less-efficient, legacy codecs if the infrastructure used in the media consumption chain is not compatible with the newer codec. For example, a DVB-S provider would broadcast signals in MPEG-2 if the consumers do not have Set-tops that can decode MPEG-4 ASP or H.264.
We can classify applications that use codecs in three broad categories:
Enterprise Media Distribution
Broadcast software and high-end encoders for film and animation are the typical examples of enterprise media distribution. For most applications of this nature, high PSNR values (peak signal-to-noise ratio) and media fidelity are of paramount importance. To encode vast amounts of data, at the highest quality possible, computing clusters are used with higher profiles of H.264 being the preferred codec. Legacy codecs, such as MPEG-2, also may be used based on the constraints of the distribution and decoding infrastructure.
Consumer Electronics Appliances
Codecs for consumer electronics appliances depend on the video media that it must encode or decode. Codecs for this class of devices are implemented in hardware because flexibility is a low priority. Legacy codecs like MPEG-2 remain widely used. However newer appliances support full HD video decoding with H.264 High Profile.
Desktop Applications
Desktop applications are used for decoding video for viewing or encoding data from attached capture devices, such as webcams, or transcoding media from one form to another. The design priority here is acceptable quality of media and a responsive application. For this, codecs such as lower profiles of H.264, WMV and MPEG-4 Part 2 are preferred. Multimedia product companies also may require that media created using their software be stored in the prescribed container format of their choice. Some media may require DRM policies to be applied and would require container formats that can incorporate and interpret the policies. MP4 or custom formats such as ASF, QT or a customized format can be used to implement such a requirement.
Web-based Media and Media for Handhelds
For streaming media and media used on mobile phones or other handhelds, the priority is a small footprint to minimize download time and a simple codec to save processing power and battery life. 3GP is the preferred codec container for mobile device media. Lower profiles of video codecs are preferred for fast decoding and reducing power utilization.
Conclusion: A Case Study - Video Codecs for Mobile Multimedia Editing Application
A well-known firm creating desktop multimedia editing software wanted to allow consumers to use their mobile phones to create videos. The firm had unique and popular features for their desktop software. To ensure customer delight, the team wanted to ensure that the mobile application would provide the “wow” factor to consumers.
Mobile Phones present an intriguing challenge to software designers. While they allow consumers anytime, anywhere access to multimedia content, their less-powerful chipsets and memory impose significant restrictions in terms of memory utilization and CPU processing. In addition, the mobile phone’s small GUI presents enormous challenges to create a user interface that is user-friendly and intuitive. In order to focus the effort on differentiating features, such as the user-interface and usability, while allowing the application to access advanced features of each codec such as the DolbyTM channels, close captioning etc., the firm decided to use Celstream’s software codec libraries for their software application development efforts. Celstream’s uniform APIs for accessing codec parameters from a bit stream or file enabled the firm to develop the multimedia editing application without the software developer having to worry about the specific codec of the AV file.
The technologies that were used include: 3GP and 3GP2 container formats, MPEG-4 Part 2 encoder and decoder, MP3 decoder and AAC encoder and decoder.
About the authors:
Ranga Raj is Chief Technology Officer for Celstream Technologies. He has more than 20 years of experience in design, product marketing and technology consulting in the IT, media and telecom industries. A member of the Celstream team since its inception, Raj has authored and presented several papers at global events and conferences, and holds a bachelors’ degree in physics and an engineering degree from IISC Bangalore.
Akbar Ladak is a Technical Manager at Celstream Technologies. His work focuses on Media & Entertainment Consulting & Software Development of Multimedia applications. He holds an M.S. degree in Electrical Engineering from Georgia Tech. He can be reached at akbar.ladak@celstream.com
