Frequently Asked Questions – TV Without Borders

These are some of the more common questions that appear in my inbox, or in the JavaTV and MHP forums.

General questions.
Migrating to MHP or OCAP.
Implementations and tools.
Implementing MHP, OCAP, or JavaTV.
Developing applications.
Extending MHP and OCAP.
About me, the site, and related topics.
Supporting the site and contributing.

General questions

When should I use MHP/OCAP/ACAP?
The various open standards can be used in almost every interactive TV system, within reason. There are some obvious restrictions that apply, however:
- MHP is designed for use in DVB systems (satellite, terrestrial, or cable)
- ACAP is designed for use in ATSC systems (satellite, terrestrial, or cable)
- OCAP is designed for use in OpenCable systems (ATSC based, cable only)
This means that the type of network you’re running on will affect your choice of middleware. However, the three standards have enough similarities that choosing one over the other may not be a big deal: South Korea, for instance, uses all three middleware standards on different types of network.

Of course, there are proprietary middleware systems out there as well, and it may well make business sense to choose one of those instead. The availability of open standards for iTV doesn’t mean that proprietary solutions are going to go away.
When not to use MHP/OCAP/ACAP
If the current crop of open standards are not designed for your network (e.g. an IP-based network) then you may want to consider using another middleware solution. Specifying all the details needed may take too long and be too high-risk. Similarly, don’t choose MHP or OCAP if you’re not planning on deploying interactive applications. Adding middleware for the sake of it is not a sensible move.

Finally, you may not want to deploy one of these middleware standards when you have a large number of low-end receivers already deployed. The Motorola DCT2500 receiver, for instance, will not run MHP or OCAP, and so JSR 242 (‘On Ramp to OCAP’) may be a better choice. This may be a slightly risky approach, though, because the danger is that you’ll move to a partial solution but then fail to move all the way to MHP or OCAP. JSR 242 is designed as an interim solution, but we all know that interim solutions have a nasty habit of becoming permanent.
Can I use my TV tuner card with JavaTV?
JavaTV is a set of APIs for building digital TV applications, and so it can only be used with digital TV signals that include JavaTV applications. It’s not designed to be used with an analog TV tuner, and so the answer is probably ‘no’. It may be possible to build a JavaTV implementation that works with a TV tuner card that supports digital TV services, but to date no company provides a JavaTV implementation with such a card .

Migrating to MHP or OCAP

How can I migrate from MHEG to MHP?
The simplest way to do this at the moment is to use an MHEG engine written in Java. Strategy & Technology sell an MHEG engine that can run as as MHP application, and so this allows an MHP receiver to run legacy MHEG applications.

It is possible for a receiver to run native MHEG and MHP middleware stacks simultaneously, but the complexity of this approach is much higher and I’ve yet to see a good justification for doing it.
What about migrating from OpenTV or another proprietary middleware solution?
OpenTV and MediaHighway middleware both have support for MHP available as optional modules, as does the NDS Core middleware. This is the easiest migration path, although licensing costs may be significant.
What is the Portable Content Format?
The Portable Content Format (PCF) is a common file format for business to business interchange of interactive TV content. It is absolutely not another API or middleware! It is designed to be translated into a network specific format before distribution to end-user’s TVs and STBs. A good use case for PCF usage would be a UK broadcaster who could create content in PCF and then distribute it to the cable operators (for translation to HTML+JavaScript), to satellite (for translation to OpenTV) and to terrestrial (for translation to MHEG-5).

PCF isn’t complete yet, and so there is no formal specification available for it. It will use XML as the basic file format. The specification will offer a super-set of features available on any individual platform. True content portability will require content creators to know the capabilities of the platforms they are targetting and to limit themselves accordingly. DVB will define some profiles of PCF to give structure to this.

Implementations and tools

What free MHP implementations are available?
There are several options that you could look at:
- XleTView – an open source Xlet emulator released under the GPL. This is missing most f the MPEG-related classes, but much of the other functionality is present. You may not be able to use it for testing your whole application, but it’s a good way of getting started.
- OpenMHP – an open source Xlet emulator released under the LGPL. Similar to XleTView, but not as complete.
- MHP4Free – a free MHP implementation. This needs a Linux machine, and since all of the documentation is in German, I can’t make too many comments about it.
- A partial MHP implementation from Espial – this is very partial: it supports the JavaTV and HAVi APIs, but none of the MHP APIs. You may find it useful, though. Free registration is needed.
Each of these tools have their own limitations, and as far as I know none of them are complete. They will each support a different subset of the MHP specification, and so which if these is most valuable to you will depend on what you’re doing.
Where can I buy a developer STB?
- ADB sell receivers from their online store at https://store.adbglobal.com/store/index.php. These receivers run the Osmosys middleware
- More information about Panasonic’s Application Development Kit is available from https://www.mhp-adk.panasonic.de/adk/index.php. This includes contact information.
- More information about the IRT reference implementation is available from marketing@irt.de.
This is not necessarily a complete list, and if you have any more information about companies selling developer STBs please let us know.
Where can I buy a normal MHP STB?
Many electronics retailers in countries that have deployed MHP will be able to sell you a normal STB. Right now, German retailers are probably the most likely to support on-line ordering for international customers.

Retail MHP boxes may not be suitable for software development, and so you should make sure that a receiver will do what you need.
Can I run MHP on my PC?
Osmosys and Zentek both have PC-based solutions for MHP. The free implementations we mentioned above will also run on a PC, but many of them are not complete MHP or OCAP implementations.
Can you recommend an authoring tool?
Not really. I do most of my MHP development using a text editor and javac, which seems to be a fairly common approach among developers. The tools may be useful, but they are not essential.

Some of the tools are aimed at building specific types of applications based around predefined templates, and you may find a given tool too limiting if you want to do something out of the scope of those templates. The best advice I can offer is to try a number of the tools and see which one works for you.
Where can I get classes to compile against?
Up to now, there has been no freely-available file containing the stub classes for MHP that developers can compile against. Licensing restrictions from Sun have prevented this, and other companies aren’t willing to give this away. Luckily, for you, we will soon have a set of stub classes that we have placed in the public domain. These do not include any intellectual property from other companies, and so they are free to use for whatever purposes you see fit.

These are only stub classes, however, and so you can’t use them to run you MHP application. For that, you need an emulator such as XleTView or a real MHP receiver.

Implementing MHP, OCAP, or JavaTV

Can I use MHP with other technologies like DVB-H, MPEG-4, or DVB-IP?
There has been no formal specification about how MHP should work with DVB-IP, MPEG-4 or other transport or video formats. This doesn’t mean it can’t be used, just that different systems are unlikely to be interoperable. A telco may choose to use MHP for interactivity of IP-based DTV networks, but they had better make sure that they specify everything that needs specifying.

MPEG-4 defines the MPEGlet concept for using Java applications – this is not MHP, and network operators and developers nee dot be aware of this. The basic lifecycle is similar, but there are a lot of differences as well.

GEM defines some mechanisms where MHP can work with non-DVB or non-MPEG systems, but this still leaves a lot to be specified.
What is GEM?
GEM is a subset of MHP that removes any of the DVB-specific elements. This allows it to be used as the basis of other interactive TV standards such as OCAP, ACAP, or ARIB B.23. There are two main parts to GEM: the list of components from MHP that are part of GEM, and a mechanism for replacing or extending GEM components in order to meet the needs of a particular market. These replacements could be made for technical reasons (e.g. the use of DSM-C data carousels in ARIB B.23 instead of object carousels) or they could be make for business reasons, such as replacing the MHP navigator with the OCAP monitor application.
Can I build a pure GEM or a pure JavaTV implementation?
Yes, but you may need to define some extra details that are not covered by GEM or JavaTV. In particular, JavaTV doesn’t define many details about the type of broadcast filesystem that should be used, or how the receiver knows that an application is available to be started. These elements, and others, need to be specified either by the implementer or as part of a standard that uses JavaTV.

Developing applications

Can I write MHP applications in Chinese/Japanese/Korean/some other language?
Yes, if the receiver supports it. MHP only requires the locale for Western Europe, but other locales may optionally be added. The same applies to fonts, and if a font is not build in to the receiver then it could always be downloaded as part of the application.

Like every other Java system, MHP uses UTF-8 for string representation, and so there should be no major problems. MHP systems have already been deployed in Korea and parts of China, and several other Asian countries are considering MHP.
What is the relationship between Xlets and Applets, MPEGlets, or Havlets?
Typically there isn’t one, although they do share a very similar lifecycle. The differences between Xlets and other types of -let are too complex to go into here, but the biggest difference is that each of them have different APIs available and are aimed at different purposes.

It may be possible to build an application that is both an Xlet and an applet (or an MPEGLet), but it’s not easy and generally there aren’t many good reasons for doing so.
Can I play back video from a file in the object carousel?
No. That’s what video elementary streams are for. Including a video file in the object carousel would cause big problems for caching and for loading other files. If you used enough bandwidth for the carousel to avoid these problems, then you may as well broadcast the video as an elementary stream. Even if object carousel performance wasn’t a problem, the receiver may still not have enough free memory to hold all of the video.

You can fake animation using a dripfeed data source, but this may not be very smooth or very fast and it’s really only suitable for very short clips. The format of an MPEG file used for video drips must comply with the file format specified in section 7.1.3 of the MHP specification. Anything that does not meet this will probably not work, especially if it’s just some random piece of MPEG. Long clips will probably run into problems because they may use B frames, which are not supported for video drips.
I can’t get a connection working on my modem.
If you’re testing from inside your company’s network, then it’s most likely that you’re running in to problems with a firewall or other access control software. Testing tools on an MHP receiver are pretty basic, so check the obvious things first.
Can a server connect to a receiver over the return channel, rather than vice versa?
It’s theoretically possible for receivers that have a broadband return channel, but not easy. There is no way that the server can guarantee that an application will be listening for connections. Generally, there isn’t much need for a server to do this, but if you have a specific example where you think it is necessary then I’d like to hear more.
How can my application uniquely identify an STB?
You can’t. There is no way for an application to get a unique ID for a specific set-top box because of possible privacy issues. Some receivers may define a proprietary API for doing this, but this is obviously not interoperable.
How persistent is persistent storage?
MHP and OCAP make no guarantees about how long a file will remain in persistent storage. It may stay there for years, it may get deleted within a few minutes, or anything in between. The main reason for this is to give the receiver a way of managing storage, so that one application can’t use all of the space in the persistent storage and prevent other applications from storing anything..

For this reason, applications can’t assume that a file they stored in persistent storage will still be there. Some receivers are known to delete files in persistent storage when the power is cycled, and so it’s best not to rely on persistent files for storing personal information or information about customizing an application.
How long will stored applications be stored in the receiver?
Typically, stored applications will stay in the receiver for a little longer than other persistent files. At the same time, they may be removed automatically after a certain amount of time or if the application storage area is full. Again, network operators should not assume that a stored application will remain stored.

Extending MHP and OCAP

Does MHP include an XML parser?
An MHP or OCAP implementation may include an XML parser, but applications will not have access to it. Any application that wants to parse an XML file must do it itself, either by writing your own parser or by using an open-source parser such as NanoXML.
How can I communicate with a smart card?
MHP 1.1 includes support for access to non-CA smart cards via the embedded version of the Open Card Framework. However, this will be replaced in future versions of MHP 1.1.x with a subset of the Security and Trust Services API from JSR 177.

MHP 1.0.x does not include an API for communicating with smart cards, but some bodies such as the DGTVi in Italy do specify that MHP receivers in those markets should include smart card support. Italy has specified that receivers should support the same subset of JSR 177 that will be adopted in MHP 1.1.x, and it’s likely that other markets that need smart card access will follow suit. Again, this API is for use with non-CA smart cards only. Theorg.davic.net.ca and org.dvb.net.ca packages provide access to the smart cards in the CA system.
How do I use external software components within my application?
Just like you would use any other classes. There are no special requirements for using other components, although you will obviously need to check the licenses that apply to those components and you’ll need to make sure that the application can load them. The easiest way of doing this is to make them part of your application and include them below your application’s root directory, but this may not be the best approach if you want to share them with other applications

You should not use any components that are not part of the MHP/OCAP specification unless they are broadcast as part of your application or in a carousel that you can use. A component may be present on one platform, but that’s no guarantee that it will be there on other platforms.
How can I share a component between different applications?
There are three options for doing this:
- Include them as part of each application. This is wasteful if it’s a big component, or if many applications will be using it.
- Put them is the same carousel as your application, but use a separate directory and include them via the classpath. This is a good middle option, but means that only applications in that carousel can use the component.
- Put them in a separate carousel, then let the application load them via a DVBClassLoader. This may reduce carousel sizes and make applications quicker to load, at the expense of some extra complexity in the application. This approach does allow you to load files from a carousel in another transport stream, provided you tune to that transport stream first.
It’s possible to combine the second and third approaches, depending on how your applications are organized and which components you want to share.
How do I support some other media type in MHP (e.g. MP3)?
With great difficulty. MHP supports a limited number of content formats because those are the ones that receivers typically support and adding a whole load of optional formats is next to useless because you can’t guarantee that they will ever be supported.

For some graphics formats, it’s possible to decode them in Java and display them. For audio and video formats this is extremely hard, and so we suggest that you don’t even try. By using the standard formats, you are avoiding any possible performance problems caused by slow decoding of the content, and you’re generally making life easier for yourself.
What HTML support is included in MHP?
Both MHP 1.1 and OCAP 2.0 include support for HTML applications. Unfortunately neither of these are deployed at the moment, and the versions of HTML that is defined by these standards will probably undergo some fairly major changes in the near future to harmonize with ACAP.

For MHP 1.0.x and OCAP 1.0 systems, supporting HTML involves downloading a microbrowser to the receiver as a normal interactive application. This approach is used in Finland and Germany for Teletext services, and it seems to be pretty successful. Most of the browsers in use support XHTML and CSS 2.0, so they offer a pretty good solution for companies that want HTML.
What is the difference between DVB-HTML, OCAP-HTML, and HTML?
DVB-HTML is an MHP-specific subset of HTML. It follows the XHTML 1.0 standard pretty closely, but doesn’t include all of the modules that are defined for XHTML. Similarly, it doesn’t include all of the features defined in CSS 2.0 but it does add a few new ones for supporting TV-based application such as a new media type, support for different aspect ratios and screen resolutions and window positioning. DOM support in DVB-HTML includes a few extra features as well, such as integration with DSM-CC stream events and extensions to support the new CSS additions. To manipulate this, DVB-HTML supports ECMAScript (not JavaScript, but a subset of it) with extra features for talking to the DVB-J APIs.

OCAP-HTML is basically DVB-HTML with a different name.

Many people are claiming to support DVB-HTML or a subset of it, but this subset may not be very different from normal XHTML and CSS. If you’re looking at using DVB-HTML, make sure the browser that you choose supports the features that you need. Most users of HTML today in MHP are mostly sticking with standard XHTML rather than using the DVB-HTML extensions. Doing this means fewer changes when DVB finally gets round to updating the DVB-HTML chapter in MHP 1.1.

About me, the site, and related topics

Who are you?
I’m a guy who’s been working with MHP since the very early days and who enjoys working with digital TV. There are a few more details on my personal pages.
Why are you doing this?
Partly because it’s a way of giving something back to the industry, and partly because the more people who are using MHP, the easier it is for me to find work. Mostly, though, this whole site is one giant advertisement for my skills. If you think that your company has an interesting job available for an MHP/OCAP/JavaTV expert, please let me know.
Why do you take so long to reply to email?
This is not my day job. Sometimes, I will be too busy at my normal job to reply to email or update the site for a while. I will try to reply to every email that I receive, so please be patient. Repeatedly mailing me to ask why I haven’t replied to your email is more likely to annoy me than to make me respond to your question.
Can I use your notes in a training course/university lecture course?
Not without paying me. All of the material on this site is copyrighted, and must not be reproduced without my permission. If you want to do this, please email me and we can reach an agreement. By the way, I do look at my website logs, and I do know who is downloading copies of the entire website.
How can I get a copy of the book?
You can buy a copy from amazon.com or from my publisher’s web site.
Can I get a bulk discount if I buy lots of copies?
Possibly. If you are looking at buying in bulk, please email me and I can put you in contact with someone at the publisher to discuss bulk rates.
What about reusing your source code?
Any source code is in the public domain. All I ask is that you let me know if you find any bugs in it.
I’m a university student doing a project on…can you help me?
I’m happy to answer questions, but please don’t expect me to do your homework for you. This applies to everyone equally, but students need to be especially careful. If you found this site, it probably means that your tutors and lecturers know about it as well 🙂

The answers you get may be more or less detailed, depending on how busy I am and what other sources of information are out there on the subject in question. If your question is answered in the MHP or OCAP spec, then you’ll probably just get a link to the appropriate document.
What is your relationship with the standards bodies?
There isn’t one. This website is not affiliated with any standards body or company. I have a personal relationship with some of the folks who are working on the standards, but I do not speak for them and have no special knowledge about what’s going on in the standardization process. I only have access to the publicly-available information that is released by standards groups and companies working with DTV.
Will you act as a consultant for my company?
I work full-time for another company, which means that my time to work on MHP/OCAP is limited. I may be able to provide some consultancy services, but this depends on a number of factors. If you are interested, please email me.

Supporting the site and contributing

How can I support the site?
The best way is to buy a copy of the book. The money from that will help to keep the site going. If you want to donate money more directly, please let me know.

Job offers are always welcome, but depending on the timing and the exact position, I may not be able to take you up on it. it’s worth asking, though.
I have some example code that could be useful.
We’re happy to publish additional example code, but we do have a few guidelines for any code that is submitted:
- Please submit a working Xlet where possible
- Please test your code before submitting it. If you know of problems on a specific receiver, please let me know.
- If you want to attach a specific license to your code, please let us know when you submit it.
- Please include written permission for us to reproduce your code from the copyright holder. This avoids any nasty copyright issues in the future.
- Any code should include comments that actually help people understand what is happening.
We may add extra items to this list in the future if we think they’re necessary.
Can I submit articles for the site?
If you have an article that you think would be useful for the digital TV community and that would be suitable for inclusion on the site, please contact webmaster@tvwithoutborders.com to discuss submission. As for example code, we have a few guidelines for submitted articles:
- We reserve the right not to publish articles that are submitted for any reason.
- We reserve the right to edit articles as we feel is appropriate, although we will seek the agreement of the author before publication
- The author of the article is responsible for clearing any copyrighted material that is included in the article, and will provide a disclaimer indicating that they have any permission they need
- All articles should have correct spelling and grammar. Any articles that have not been spelling or grammar checked will be rejected.
- All articles should be written in English. Articles in other languages will not be accepted because of the difficulties of checking them.
Again, this is not necessarily a complete list and more items may be added at any time.
Can I translate your site into another language?
None of the contents of this site may be translated. The pain of checking translations for correctness and factual accuracy is simply too high for us to cope with.
I would like to use some material from your site in a paper/book/article.
First, thanks for asking. We’re usually happy to grant permission for using quotes or images from the site in other articles, but please check with us first. It’s important that you identify exactly which images or text you would like to use, so that we can make sure we are the copyright holder and that we grant you rights to use the correct content.

Please note that you are not allowed to reproduce the entire site or entire articles.
How do I get my company’s name in the listings?
Please email a short description of your company and your website URL to info@tvwithoutborders.com.
How can I contribute press releases and news stories?
Again, please email the press release/news story and a URL for the story to info@tvwithoutborders.com. The full text isn’t so important as long as you include a URL, but it’s useful.