So, what features should you look for in a portable DVD player?

Portability: Size is important with any portable device. Mere millimetres can make all the difference and nursing extra weight can turn a pleasure into a pain. Weight can vary by up to a couple of kilos, especially if a player has large rechargeable batteries. Leading players in the 7-8in range are only slightly bigger in size than two DVD cases stacked together.

Supported formats: Doubling as a CD "Walkman" is just the start, portable DVD players usually support many other formats, including recordable DVDs (DVD-R⁄-RW, DVD+R⁄+RW), plus VCD & SVCD format discs, MP3s and photo discs (Kodak Photo CD and JPEG files).

Some newer players also incorporate leading edge features like support for newer video compression technology like MPEG-4 and DivX. The DivX format in particular is gaining popularity for its high compression without sacrificing quality (for more information go to www.divx.com).

Many players will add support for NTSC (American video standard) to our PAL system, which combined with multi-region support, enables you to play discs from other regions (eg, the US is Region 1 and Australia is Region 4). For more info see www.dvddemystified.com/dvdfaq.html#1.10

Output connections: Being portable means being versatile, so make sure the player you choose has the plugs you need to connect to other devices - eg, S-Video for video out and Optical Out for audio - for the best picture and sound quality, especially when substituting for their larger cousins. Dual headphone jacks are great for two-person viewing.

Screen: Built-in screen size can vary and though you want the smallest, slimmest device for the ultimate portability, you also want the biggest screen. Of course, the larger the screen the heftier the price. A 7in screen is pretty much standard among quality players, but size can vary from as little as 4in up to around 10in or even 12in. A 16 by 9 aspect ratio is preferable as this is the format adopted for widescreen DVD and High-Definition TV viewing, as is higher-quality progressive scan video support. However, look for a unit that also supports the older 4:3 aspect ratio (similar to the picture on a standard "square-screen" TV set) for maximum use of the screen when viewing non-widescreen material.

Some portable DVD players even come without a screen and must be connected to an external TV or monitor. They are usually cheaper but obviously less versatile.

Sound: When you can't hook it up to a home entertainment system, your player still needs to give out decent sound - preferably stereo and even better, virtual surround sound for a more realistic "big screen" feel from its built-in speakers. Support for Dolby Digital and DTS decoding give you true 5.1 sound when external speakers are added.

For private viewing, you may opt for headphones. Look for a player with two headphone ports, or get a Y-plug headphone splitter, so more than one person can listen in.

When you are looking for better sound in the car, one solution is to play the audio through the car's stereo system using an audio cassette adapter, which plugs into the line-out or headphone jack of the player. The cassette module plugs into your car's stereo cassette player.

Another method is to use a portable FM transmitter (eg, the Belkin Tunecast at around $50), which plugs into the DVD player's line-out or headphone jack and transmits the audio to an unused FM station on the car's audio system. The only drawbacks with this is that on long trips you may have to retune it from city to city, depending on station availability and moving the transmitter around can cause static and interrupt the frequency.

Power: The ability to charge from multiple sources is ideal for travelling and a player will generally come with an AC adapter and possibly a DC adapter for in-car use. Some players will have a detachable battery which can be charged separately from the player. Look for at least two hours continuous playback ability for uninterrupted viewing of a whole movie when you're unable to plug-in. Some players last up to five hours before recharging. Rapid charging and the option of a second battery are also advantages . Two smaller, thinner batteries may be preferable to one larger battery, which will add extra size and weight to the player.

Remote control: If the player is in your lap on a plane, you obviously won't need this, but with the player plugged into a large TV across the room the remote control is a necessity.

Viewing angle: Not everyone can sit right in front of the player and viewing quality on flat screens can drop off quickly the further you go from this central point, so a wide viewable angle is a must - for viewing by two people in the back of a car, for instance. The wider the viewing angle the better. A viewing angle of up to 160 degrees can be achieved with a high-quality TFT (thin film transistor) flat screen common on today's portable devices.

You-beaut features: Newer models are coming out with more than mere DVD/CD/music playing capabilities, such as the MPEG-4 and DivX support mentioned earlier. Add to that an internal hard disk drive and recording capabilities and possibly even a built-in TV tuner and you have a laptop-sized equivalent of a DVR (digital video recorder)-based home entertainment system.