Assessing the tradeoffs between implementing video-processing tasks in hardware on function-optimized silicon, in software running on a general-purpose microprocessor, or (as an intermediary approach between these two extremes) in software running on a multimedia-tuned DSP has long fascinated me. Unique application criteria in each particular design situation mean that no one approach is optimum in every possible case. Consider, for example, the endpoints of the spectrum of possible implementation options. Function-optimized hardware is often the lowest-power-consuming approach, and it can also be the most cost-effective. Conversely, you're out of luck unless you wish to implement exactly the algorithms frozen into silicon, as compared with the infinite flexibility of code executing on a CPU. And the relative cost argument is a moot point if the system you're designing is intended to be (for example) a peripheral to a computer already containing a beefy x86 µP, versus a standalone system.

This particular Prying Eyes project is emblematic of these pros and cons. It compares and contrasts two Plextor-branded products, both purchased on closeout, with similar advertised functions. The less expensive unit even offers a TV tuner absent from its pricier peer. Plextor's ConvertX PX-TV100U cost $8.99 after rebate ($38.99 before, $99 original MSRP), while the PX-M402U was $29.99 after rebate ($99.99 before, $159 original MSRP). The difference between the two centers is a software-versus-hardware compression emphasis. The PV-TV100U relies on the CPU horsepower of a USB2-tethered PC to handle the hefty audio-plus-video lossy compression duties, whereas the PX-M402U harnesses its integrated WIS Technologies G07007SB streaming-media encoder for these meaty tasks. The G07007SB natively supports multiple video inputs; conversely, with the PV-TV100U, input switching is handled by two Philips (now NXP Semiconductor) 74HC4052 analog multiplexer/demultiplexers (one on each side of the PCB).

Speaking of inputs, both devices need to translate incoming analog multimedia information into digital equivalents. With the PX-TV100U, audio and video conversion are respectively the domains of Micronas' MSP 3425G (PDF) sound processor and Texas Instruments' 5150AM1 video decoder. The PX-M402U, conversely, relies respectively on AKM Semiconductor's 5355 (PDF) dual-channel 16-bit audio ADC and NXP Semiconductor's SAA7115 video decoder. Whereas the SAA7115 comprehends NTSC, PAL, and SECAM video standards, the video decoder in Plextor's PX-M401U (the PX-M402U's predecessor) supported only NTSC. Another key difference between the PX-M401U and follow-on PX-M402U is that the latter, later device was explicitly certified by DivX. I suspect, however, that both products employed the same WIS G07007SB compression engine, which supports MPEG-4, MPEG-2, MPEG-1, Motion JPEG, and H.263 video codecs. The DivX format, after all, is a combination of MPEG-4 video and MP3 (MPEG-1 Audio Layer 3) audio bit streams bundled together by a proprietary “wrapper.”

On the other end of the processing chain, raw audio and video conveyance from the PV-TV100U to a PC is the responsibility of Empia Technology's EM2860 USB2 media-capture processor, whereas the USB2 transport of already-compressed multimedia data from the PX-M402U falls to Cypress Semiconductor's CY7C68013 embedded microcontroller. Both products include serial EEPROMs; an Atmel 24C01A 1-Mbit device in the case of the PX-M402U and a Catalyst Semiconductor (now owned by ON Semiconductor) 24WC02 2-Mbit memory for the PX-TV100U. The PX-M402U also embeds a 64-Mbit PC100 SDRAM, Micron Technology's 32-bit interface 48LC2M32B2. The not-shown backside of the PX-M402U PCB, by the way, is devoid of ICs; all you'll find there (aside from traces and solder points) are a scattered few passive components, such as capacitors, diodes, inductors, and resistors.

When examining a piece of gear, I always enjoy seeing how it's been intentionally made adaptable by its designers to support multiple product proliferations spawned from a common hardware foundation, and differentiated by minor peripheral variations and unique software builds. Flexibility within the PX-M402U design is exemplified both by unpopulated primary PCB sites and by sufficient spare space in the enclosure for a supplemental PCB-housed TV tuner to transform the unit into a PX-TV402U. Reflective of this malleability, the unit's rear panel is easily removable, therefore replaceable by one incorporating a coaxial cable connector. Some of the unpopulated primary PCB sites are, I suspect, intended for primary-to-secondary PCB bridging purposes.

Note, too, the unused areas on the PX-M402U PCB intended for a second set of analog audio connections and both composite and S-video ports. Inputs or outputs; who knows? Plextor never brought to production a variant of the PX-M402U that employed them; I suspect the company leveraged a generic WIS Technologies reference design. Similar flexibility can be found in the PX-TV100U, which includes a LG Electronics “can” tuner. Plextor also sold a tuner-less variant of this same design called the PX-AV100U.

Because the PX-M402U and PX-TV402U don't rely for compression duties on the system they're connected to over USB2, they're more adept at supporting various tethered equipments' operating systems, as compared with the Windows-only PX-TV100U. They quickly became, for example, PVR hardware favorites of Linux users. Specifically, it's possible to transform a Sony PlayStation 3 into a PVR, by virtue of the game console's built-in USB ports and its capability for running Yellow Dog Linux and other open-source distros.

1.  Plextor’s PX-TV100U relies on the CPU horsepower of a USB2-tethered PC to handle the hefty audio-plus-video lossy-compression duties. The PX-M402U harnesses its integrated WIS Technologies G07007SB streaming media encoder for these meaty tasks.

2.  Raw audio and video conveyance to a PC is the responsibility of the PV-TV100U’s Empia Technology EM2860 USB2 media-capture processor. The USB2 transport of compressed multimedia data from the PX-M402U falls to Cypress Semiconductor’s CY7C68013 embedded microcontroller.

3.  The PX-M402U design offers flexibility in both primary PCB (printed-circuit-board) unpopulated sites and sufficient enclosure space for a supplemental PCB-based TV tuner that would transform the unit into a PX-TV402U. Similarly, although the PX-TV100U includes an LG Electronics “can” tuner, Plextor also sold the PX-AV100U, a tunerless variant of this design.

4.  Both devices need to translate analog multimedia information into digital equivalents. With the PX-TV100U, audio and video conversion are the domains of Micronas’ MSP 3425G sound processor and Texas Instruments’ 5150AM1 video decoder, respectively. The PX-M402U, conversely, relies on AKM Semiconductor’s 5355 dual-channel, 16-bit audio ADC and NXP Semiconductor’s SAA7115 video decoder. Whereas the SAA7115 comprehends NTSC (National Television System Committee), PAL (phase-alternating-line), and SECAM (Séquentiel Couleur Avec Mémoire) video standards, the video decoder in the PX-M401U (the PX-M402U’s predecessor) supported only NTSC.

5.  Both products include serial EEPROMs: a 1-Mbit Atmel 24C01A device in the PX-M402U and a 2-Mbit Catalyst Semiconductor 24WC02 memory for the PX-TV100U. The PX-M402U also embeds a 64-Mbit, PC100 SDRAM, Micron Technology’s 48LC2M32B2 with a 32-bit interface.