iTunes Video Quality vs DivX

I finally found some free time this week to watch the modern Battlestar Galactica TV series, which I bought from the iTunes Music (neÈ video) Store. (As an aside, Battlestar Galactica is absolutely awexome — but that’s a whole ‘nother story).

I actually have DivX versions of the episodes that can be obtained from the usual places where people obtain DivX versions of TV episodes. I decided to buy the episodes from iTunes anyway, to see how they’d compare in quality to the DivX ones. I’m not particularly surprised to say that the quality of the iTunes videos are slightly worse than the DivX versions floating around: there are some people who are pretty damn crazy and spend weeks tweaking their DivX video encoding parameters to make them look really good. Thanks to the rabid fanbase on P2P distribution networks that demand very high video quality, you also generally find that most videos on P2P networks have been lovingly hand-tweaked and encoded quite well.

(Note: I’m using the term DivX to mean the whole plethora of MPEG-4 video codecs, such as the “real” DivX, xvid, 3ivx, etc. You can start endless debates about which codec is better than the rest for encoding particular types of motion video, and that’s not my goal here.)

However, even though the iTunes video versions aren’t quite as good quality as the DivX versions that you find floating around on the ‘net, it’s not quite that simple:

  • First, I was playing the videos on a 1GHz Powerbook G4, which may not quite be powerful enough to do decent post-processing on the H.264-encoded video. iTunes uses QuickTime for its video playback, and QuickTime is a pretty adaptable beast: if your CPU isn’t powerful enough to perform decent post-processing, it simply will make the frames look worse rather than dropping frames, even resorting to simple linear sampling to perform scaling if absolutely necessary. It’s entirely possible that the videos would look much better on a high-end computer such as a modern Athlon system or a Power Mac G5.
  • The iTunes videos were encoded at 320×240, which is much lower than typically encoded DivXs (the Galactica DivXs that I had were encoded at 640×352). This also means that the iTunes videos weren’t widescreen, for those of you lucky punks who have 16:9 screens.
  • I was playing the videos on a TV, which has a lower resolution than on a computer monitor. The raw resolution of the videos don’t make such a big difference because of this, which partially negates the last point. I should point out that the TV I was watching it on was pretty big (42”), so it’s still very easy to see encoding artefacts.
  • The iTunes videos were much more colour-accurate than the DivX versions: all the DivX encodes I’ve seen were far less saturated. (I’m sure that it’s possible to get DivX versions that are more colour-correct; I’m just going on the DivX videos that I have.) A/B’ing the iTunes video and the DivX on the TV, I’d actually say that the richer colour on the iTunes version more than compensated for the DivX’s increased resolution, and made the ‘feel’ of the video better overall. Except…
  • There were some very visible blockiness during the space combat sequences of Battlestar Galactica: outer space is quite black, and the H.264 encoder that Apple uses on its videos decided to seriously quantize the black bits and produce large blocks of visible non-colour-matching blackness. I suspect this would be less of a problem for non-sci-fi series, and this problem didn’t come up very often, but the encoding artefacts were bad enough that they did detract from the whole cinematic experience when they appeared.
  • The iTunes videos were much smaller; part 2 of the Battlestar Galactica mini-series was ~400MB for iTunes, vs ~700MB for DivX.

Overall, I was generally happy with the iTunes versions of the TV episodes except for the blockiness during the space combat scenes. It’d be interesting to play the episodes on a PC or Mac with some grunt (or a 5G video-capable iPod), and see if the blockiness disappears due to better post-processing. If it does, I’d be tremendously happy with them.

So, if it were pretty much any other TV series, I’d be pretty happy with buying them from the iTunes store, but Battlestar Galactica is looking like it’ll be my favourite hard(ish) sci-fi series ever, so I’ll probably hunt down the HD broadcasts or buy the DVDs at some point. I feel that the USD$2 per episode at the iTunes store is very well-priced, and that it’s cheap enough to sus out a couple of episodes before deciding that (a) you’re happy with the quality, or (b) you’ll chase down the DVDs because the quality isn’t good enough for you and you’re a big fan of the show.

Obviously, there are other reasons besides just technical ones in the iTunes store vs P2P debate, such as where you personally lie on the ethical compass about giving money back to the people who produce the series and the distribution houses, what your stance on iTunes’s DRMS policy is, and also the ease of buying stuff on iTunes vs the ease of searching on P2P networks. I think that the videos available on the iTunes store are a good first step in the right direction, though. Technically, though, I’m reasonably happy with the iTunes videos, and would certainly buy from the store again.

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