May 8th, 2011
Netbooks have proven to be extremely useful tools for games journalists, offering extremely mobile computing with great battery life – great for live-blogging and event coverage in general. Following a discussion on the DVInfo CineForm forum, I wondered whether these useful little mini-laptops could actually be re-factored into an ultra-cheap 10.2″ battery-powered HD capture unit when used in concert with our forthcoming Expresscard-HDMI offering.
The odds are stacked against us. Current laptop CPUs use up to 45 watts of power, but the Intel Atom CPU found in netbooks only requires a miserly 2.5 watts. Indeed, the surrounding chipset soaks up far more power. Designed for minimal applications – running Windows, a browser and Office – the 1.6GHz Atom’s performance has been equated to an aged Pentium M running at half the clock speed. That’s six to seven year old CPU technology. Asking for real-time compression of HD video with such meagre power seems almost too ridiculous to contemplate.
For our purposes, the CPU has to compress 720p input at 60 frames per second to such a degree that the footage can be streamed onto a 2.5″ notebook hard disk – a drive inherently slower than desktop equivalents. Not only that but it needs to sustain a full frame-rate real-time preview window, so you can actually see what you’re capturing. For the Atom platform, this is a bit of a problem in itself as the chipset uses CPU to emulate the hardware overlay required for the preview, sapping precious processing resources. On top of that, ideally we’d also like to run the display cloned onto a monitor via the VGA output – squeezing RAM and bandwidth.
It’s alive. In this video you are seeing an Intel Atom netbook capturing Bayonetta – one of the most problematic compression challenges available – via HDMI at 720p60, using the AmaRecTV software package in combination with the AMV codec. An h.264 MP4 of the actual video that was captured is available to download here. The AmaRecTV tool gives some useful stats – no dropped frames at 720p60, though the real-time preview window hovers around the 57fps mark. While the tool registers Expresscard-HDMI as “S-Video”, the card is merely using the S-Video channel – this is digital HDMI all the way. A TrueHD workstation was used to record the VGA and headphone output of the netbook.
The first challenge was to find a netbook with the Expresscard slot. They’re not so easy to locate as Expresscard is typically only found now on business-orientated laptops and, as far as we know, there is no modern machine currently in production that combines this slot with an Atom – aside from a Gigabyte tablet unavailable in the UK and grossly expensive any way.
Fortunately, what this does mean is that the units which are capable can be cheaply acquired on eBay. What you’re looking out for are machines such as the ASUS N10J (which has dedicated GPU and an HDMI output), Lenovo S9e, Lenovo S10e and the HP Mini 2140. N10J aside, they all have the same core innards – the N270 Atom and the lacklustre 945GC chipset. The ASUS machine most likely offers the best functionality, while the HP Mini is undoubtedly the coolest, looking rather like a miniature Macbook.
The machine I located was a bit of an oddity – a Vye V81006 – a netbook I believe was solely distributed to certain UK educational establishments. £88 on eBay makes it a bit of a bargain and while I would have preferred an ASUS or HP, the cheapest I’d seen them for was around the £130 mark. The Vye came with 1GB of RAM and a Toshiba 160GB HDD, which luckily proved to be quite fast. Fast HDDs are good news for this experiment because there’s not much CPU power here for compressing the image, so the faster the drive, the less compression you need.
The first test was to see if the Expresscard-HDMI card actually worked. While the Expresscard slot should offer full PCI Express x1 bandwidth, USB is also supported so the concern was that only the USB connection would be implemented. There was some initial despair as connecting the card achieved absolutely nothing. However, similar to the Macbook Pro we tried recently, the card was recognised when we rebooted. No hot-swapping support then, but the driver worked so things were looking good.
With the card established as working and the capture tool producing an image, the task then moved onto what we could do with the limited CPU power available. CineForm has talked about their encoder being able to reach 1080p at 20 frames per second on a base Atom, but with the added overhead of the capture tool and real-time preview factored in, unfortunately it proved to be too much for the Atom – even on the lower quality settings. This is a shame as CineForm is by far the most flexible and image-quality orientated intermediate codec on the market today, and a single core Pentium 4 can manage 720p30 easily.
UT Codec Suite has received plenty of plaudits as a fast, multi-core aware lossless codec but the best sustained frame-rate I could achieve on the netbook was 720p at 30 frames per second. Good enough for most uses, but not all… 720p60 should really be the target here.
So, are we really getting a full 720p60 HD capture from a netbook? And what’s the quality like? These are two shots from the Bayonetta capture session in the video above. Click through for the PNG loveliness.
Runaway winner proved to be the AMV codec, used in conjunction with the same developer’s AmaRecTV app. The faster lossless modes would encode a 720p frame in around 10-12ms, which is frankly phenomenal and more than enough for 60FPS capture, but with filesizes running at 80MB/s, a 2.5″ laptop HDD just wouldn’t be able to keep up. Even a desktop drive would struggle. Moving to the more computationally expensive lossless modes brings down the capture rate on the same material down to a more manageable 35-40MB/s, but CPU time moves up to 14-16ms. You must keep below 16.66ms in order to keep a sustained 60fps capture.
The problem here is that the additional CPU load impacts the performance of the real-time preview window. If Intel had possessed the foresight to give the Atom a chipset with a hardware-driven video overlay, this would not be a problem (and chances are that the ASUS N10J with its NVIDIA chip will take care of this and open up more encoding options with the extra CPU time) but the default 945GC chipset powers the overlay via a software driver, so the challenge then becomes a question of finding a display mode in AmaRecTV that has the least drain on available resources. Thankfully we did and sustained 720p60 capture on really challenging material was confirmed.
It’s clear that while it’s possible to record HD video on a netbook, a set-up with more CPU power is preferable. A 13.3″ laptop would do the job beautifully and in the form of something like the new Dell Latitude E6430, you have a Sandy Bridge powered machine with all the CPU processing power you could possibly need. Plus it has a modular bay optical drive that can be replaced for another battery or a secondary HDD.
But there’s still something to be said for doing it all on a netbook – by far the most flexible and portable piece of mobile computing tech on the market today, and I think that I’ll stick by the Atom-powered 1kg computer for my own portable capture needs… though if an N10J pops up at a bargain price on eBay I don’t think I’ll be able to resist it.