Yesterday I decided, on a whim, to search for a portable MP3-DVD player. This is something I've done off and on for several years now, and I always come up empty handed. As usual, I came across several forums where people were inquiring about exactly the same thing I want. The collective wisdom of the internet, once again, says that this is a product that does not exist.
What is this dream product? Well it seems simple and obvious to me--something that would have demand outside just the "geek sector," and I see no technological reason it should be infeasible--and it continues to elude me why nobody has made it. The concept is this:
Portable CD players often have the feature of playing MP3s. That is to say, you can burn a data CD (rather than audio CD) full of MP3s, and the CD player will scan the file system on the CD looking for MP3s, index them all, and then let you play them as you would audio tracks (and the nicer ones let you browse the filesystem, randomize, shuffle by directory, etc. too). Now, extend that to DVD. A single-layer consumer-grade writiable CD (typically) holds 700MB, while a DVD holds 4.3 GB of data. Such a DVD holds 6.3 times as much as a CD.
From my own personal experience, when I used to burn MP3 CDs to listen to on a portable player, I averaged about 130 songs per disc. If I could use DVD discs, I could record about 820 songs on a single disc. And unlike with an iPod (and its built-in hard drive), I can swap those discs out. To put it another way: let's say all your music fits in a 128 CD wallet. Again, from personal experience, full albums rip encode to about 75 megs worth of MP3s. That's just under 9.4 GB, or just over 2 full DVDs. That entire CD wallet you carry around, or used to carry around before you got your iPod, could be just two or three DVDs you carry around instead. And you don't have to worry about hitting that 40 GB limit you have with your hard drive, or constantly take songs off to put songs on. I don't know this part from experience, but I know how big my music collection is, and it's not getting any smaller. Also, I know upgrading to an iPod with a bigger hard drive (if you find your existing one too constraining) isn't cheap either.
So when I say DVD, understand that I'm talking about DVD discs, but not the DVD formats. This has nothing to do with video, surround sound, or any of the other DVD-Video perks. I'm just talking about using DVDs to store data, specifically MP3s, to play on a portable player. A Walkman type device, running on two AA batteries, that plays 820 songs on shuffle. Does that seem so absurd? Why isn't this type of device on the market?
- Maybe the hardware required to read a DVD won't run off two AA batteries? If not, how much juice would be required?
- Royalties due to the DVD Consortium might apply to DVD discs regardless of whether you're just storing data on it or storing a settop-DVD-player playable movie on it. If so, that would cost them per device they sell. I really don't know.
- The technology for portable DVD players may not be there. At the time I first started looking, car DVD players didn't exist yet. So the equivalent of "skip proof" type technology (error correction for a much less wide data track, under potentially bumpy conditions) wasn't there, and R&D would've been expensive for something potentially not marketable. With DVD players in cars being somewhat common now, I think this would be an easy transition.
- They might think most consumers don't have DVD burners, or are too stupid to use them. Either way, they don't see the demand being high.
- They may think consumers would be put off by going back (from hard drives) to media that can be scratched, not to mention is fairly static. Once you burn a DVD it's burned. You can either burn over it (if it's re-writeable), or hope your MP3-DVD player supports multisession discs. For the average consumer, this is less than ideal. However, this point applies to MP3-CDs too and there are an abundance of players for those.
- Update: MP3 players with hot-swappable memory sticks (SD/MMC, etc.) have been on the market for a bit now, and I hear some of you wondering why you'd want a big bulky MP3-DVD player with scratchable media instead of one of these. Right? The answer is price. 4.7 (4.3 actual) GB DVDs cost a dollar each, retail, and can be had for a quarter of that or less online. A 4 GB stick of SD will cost you $70 retail, $35 online. That's 70 to 120 times the price for the media, for the slight convenience of a smaller form factor device.
Possible reasons I can think of off the top of my head (but I have no idea how true any of them are):
 Yes, I know they're advertised as 4.7 GB, but like hard drives, that's measured in base 10 (1K = 1000 bytes; 1M = 1000000 bytes). Operating systems use base 2 (1K = 1024; 1M = 1048576 bytes), so Windows will tell you that a completely full DVD has 4.3 GB of data on it (rounded).
 I encode at 112-320Kbps VBR, generally. From a random sampling, I saw everything from 50 to over 100 megs per album, but the average was in the 70-75 range. I erred on the side of bigger albums so as not to make my argument seem better than it actually is.
 All prices were as of 8/15/2007.