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Friday, December 7, 2012

iTunes vs. DVD Information for the Quality Concnered

Overview


The purpose of this article is to discuss the merits of iTunes video quality and theoretical longevity of improving quality, versus buying DVDs with their quality.

It compares DVD Quality video (most specifically in this comparison from Amazon's DVD on-demand) and iTunes SD video. This isn't exactly Linux related, though I use iTunes through VirtualBox occasionally when I need things and *ahem* deal with the Draconian freedom suppression from Apple appropriately so I can enjoy it in Linux.

Why is this important?

Simple: If you want the best video quality you can purchase for your media, it is important to know what you will get if you purchase DVDs, or buy from online services such as iTunes, Google Video, Amazon Video, or elsewhere. In all my research online no one had concisely put all the important facts together in one place. So I had to do my own research and compile the facts, which are herein reported.

Movies (especially those available on Blu-Ray)

BluRay discs at this point are not being considered because the average BluRay movie blows iTunes off the map in terms of quality, plus you can get all sorts of extras sometimes. So a BluRay movie when you can get it is still a great cost-to-value ratio, far higher than iTunes currently. It is also unlikely that iTunes will be raising the digital quality (H26 video codec choice, audio and video quality bitrate levels, etc.) any time soon, since they just hit the 1080p mark for some content.

Results Summary

The situation simplifies down to two scenarios:
  1. If the content is available on iTunes in HD (meaning High Definition with 720p/1080p), the iTunes options is superior to even the best quality DVD you can find.
  2. If the content is available on iTunes in SD (meaning Standard Definition with 480p), the DVD options is almost certainly going to be superior to iTunes video.

    There is one potential caveat to mention. See below.
If you want more details on how I reached this conclusion, see below for some file specific comparisons.

My opinion on the matter: When  SD videos become available in HD, so will Blu-Rays of the media. Just buy those.

DVD Longevity Caveat

There is one potential caveat to mention. With iTunes there is potential for longevity. Apple recently upgraded many of their 720p iTunes videos to 1080p for free! So if you already owned it, you get it in higher quality. That's really nice. A DVD won't do that for you. But there is a twist to this generosity.

However there is no guarantee that SD video will ever be available in HD. Converting older media to remastered quality is costly and time consuming. Usually when it is done, there are also Box-sets released on the latest media. So when you see SD video remastered into HD video, you might also see a Blu-Ray Box-set for sale simultaneously.

The 1080p Twist by Apple's iTunes

This is merely an informational section: Apple very likely had the 1080p video available dating back years and years, but refrained from making it available due to playability limitations on some of their various devices. As far as the scuttlebutt on the Internet goes, Apple is handicapping content lower for one reason: compatibility with the 5th generation iPod's.

Their recent action should not be seen as a move forward, since they were consciously and actively preventing the vastly greater majority of users from enjoying superior quality, because of a very tiny few legacy users. In essence, this move was not one of going forward; it was of ceasing to suppress quality.

iTunes vs. DVD Comparison Details

iTunes does have a very very large selection of media, but not all the media is in High-Definition. In fact, most of the older media is only in Standard-Definition. For example, Hey Arnold!, El Tigre: The Adventures of Manny Rivera, Daria, and My Life as a Teenage Robot, are all only available in SD Version.
I had difficulty finding technical specs documentation. Here is what I have found so far [info source here]:

iTunes Rentals:
Apple TV HD - Main Progressive Profile at 1280xN at 4-5mps, 5.1 AC-3 Pass Through.
Apple TV SD - Main Progressive Profile at 720xN Anamorphic (creates 853xN files), likely 2.5 mbps.
iTunes SD - iPod/Basic Progressive Profile at 640xN - Now Anamorphic (which creates 853xN files), 1.5 mbps (maybe higher).

Purchases:
iTunes/Apple TV - iPod/Basic Progressive Profile at 640xN, 1.5 mbps.

Of course, Megabytes per second (mbps) are intimately tied to the codec in use. In the case of Apple Content as far as I know, it is H.264. DVDs are encoding using the MPEG-2 video methods.

Researching on Wikipedia I found this (and though it doesn't cite many sources I generally know this to be true from personal experience mucking about in video):

DVD-Video discs have a raw bitrate of 11.08 Mbit/s, with a 1.0 Mbit/s overhead, leaving a payload bitrate of 10.08 Mbit/s. Of this, up to 3.36 Mbit/s can be used for subtitles and a maximum of 9.80 Mbit/s can be split amongst audio and video. In the case of multiple angles the data is stored interleaved, and so there's a bitrate penalty leading to a max bitrate of 8 Mbit/s per angle to compensate for additional seek time. This limit is not cumulative, so each additional angle can still have up to 8 Mbit/s of bitrate available.
Professionally encoded videos average a bitrate of 4-5 Mbit/s with a maximum of 7–8 Mbit/s in high-action scenes.

So what does this mean? Well, the average DVD, even something with only 4.7GB of disc space capacity, has a considerably higher average video bitrate per second, compared against the average SD video from iTunes.

But bitrate doesn't include the differences in the video codecs for each data source, so I needed a better test.

Side by Side Comparison

For the comparison of the quality, I picked an episode from my Hey Arnold! DVDs. In particular, this episode is from Season 3, episode 11 Part 2 (or 11b), title "Hey Harold."

[Of note, iTunes may use a different episode numbering system than the established wide-spread one, based on date of initial public release.]

Below is a side-by-side comparison of the visual video quality:


As you can see there are notable differences in the visual quality. The color schemes are different, and there is noticeable picture compression on some of the subtle textures. The interlacing between the two videos is varied in sections, so I don't think I would label one as overall superior to the other for interlacing.

Obviously there is a slight frame size difference as well.

DVD episode

The video dimensions were 720x480. The framerate was 29.970 fps.

The video data amounted to 420MB for 11:48 of time. Doing the math that is 420 MB divided by 708 seconds, which is an average bitrate on screen of 0.5932 mbps.

Video format MPEG-2.

Of note, the audio quality was 16.20MB of AC3 192kbps of data.

iTunes SD episode

I put my money where my research is and bought the same episode of Hey Arnold! in SD using iTunes 10.5.

The video dimensions were 640x480. The framerate was 23.976 fps.


The video data amounted to 117.12 MB for 11:48 of time. Doing the math that is 420 MB divided by 708 seconds, which is an average bitrate on screen of 0.1654 mbps.

Video format is H.264.

Of note, the audio quality was 10.68MB of AAC 128kbps of data.

Conclusion

This conclusion is pretty straightforward for me. Looking at video bitrate alone, as well as visual quality, even non-remasterd DVDs like this can trump iTunes SD. I'm aware this is only one sample, but the cartoon Hey Arnold! has over 100 episodes that mirror this data out. That's a lot of conforming data. Even disregarding the visual differences, for the shear bitrate differences I would still go with DVD. Plus there is the freedom of playing the DVD anywhere and everywhere, contrasted against Apple's Draconian control model.

For iTunes only offers SD media, buy the DVDs instead. Otherwise, buy the iTunes HD media.

The situation simplifies down to two scenarios:
  1. If the content is available on iTunes in HD (meaning High Definition with 720p/1080p), the iTunes options is superior to even the best quality DVD you can find.
  2. If the content is available on iTunes in SD (meaning Standard Definition with 480p), the DVD options is almost certainly going to be superior to iTunes video.
iTunes SD video may be quite good for its size but it isn't as quality as most DVD video sources.

Video Alternatives

Currently these best alternative options you can find are listed below. But my conclusion is that either DVDs or iTunes are still your best bet for pure video quality. See above details for where and which.

A good table comparison is also available here: High-definition video - HD on the World Wide Web - HD Streaming

Google Video

In short summary: As of writing this (December 2012), Google Video disregarding selection of available video titles compared to its competitors, I'm actually having serious trouble finding the specifications for HD and SD video purchased through Google Play.

Some reports I have read from only several months ago claim that Google also has less HD (720p/1080p) video than their competitor(s). Unfortunately my notes don't have the citations and current Google searches fail to confirm or deny this information. If anyone wants to furnish me with detailed specs, I will be happy to list them here.

Amazon Video

In short summary: As of writing this (December 2012), Amazon Video it isn't even up to average DVD standard quality [video bitrate per second]. You can check Wikipedia articles for better details and explanation on this matter.

Furthermore, at this time Amazon Video isn't even half the quality of 720p video from iTunes.

Amazon Video appears more geared towards streaming, and their strategy currently is less about the highest quality of video available, most likely due to bandwidth limitations for most customers.

4 comments:

  1. Amazon video still uses WMV for PCs, you can view in other formats for phones but you are out of luck if you want to download.

    As for SD iTunes vs. DVD you missed a few aspects. Notice that iTunes was 23.97 and DVD was 29.97 fps? DVD is interlaced and iTunes is progressive. Additionally DVD uses the NTSC Interlaced colors but iTunes is using MPEG4 which again is better.

    I would say that iTunes MPEG4 for those 2 videos DVD loses. H264 is far more better at compression then DVD and they are using VBR (not CBR) so notsure how you are calculating it? Additionally the NTSC colors on your DVD screen show clearly shows it is nowhere near as crisp as progressive mp4.

    PAL colors are better but still interlaced video. As for your size difference DVD is stored at 720x480 but for 4:3 it is resized to 640x480 so you are using different players as 640x480 should be the same, though agreed slightly lower resolution but not smaller since DVD is anamorphic. It never displays 4:3 or 16:9 at 720x480 (I think it's 720x404 for 16:9 and 640x480 for 4:3 NTSC) as PAL is much higher at x576 :)

    SD mp3g4 on itunes (480p vs. 480i) for NTSC I would chose iTunes, there is a lossless crack to strip the DRM but not an easy find.

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  2. People ask me a lot about what exactly interlaced video is but think of it as an "analog" lossy compression. Basically most NTSC TV shows were shot on film (24 frames per second) but how do you get that to display at 29.97?

    First you slow it down from 24fps to 23.97, then you interlace the video by using "key frames" instead of 24 individual frames per second.

    So for 1 second of video the source has 24 individual frames per second, but the interlaced has much less. This varies as it takes the major part (key frame) and borrows elements from neighboring frames. 29.97 Interlaced is a much smaller file size then 23.97 (or 24) progressive. Sadly once this process is done like with mp3 you truly can't get back the lost data :(

    Any players, tvs or software that claim to play DVD at 480p/576p/720p/1080p etc. are using one of several processes like converting an mp3 back into PCM, the true frames are gone and so are the colors. So iTunes MP4 indeed has some improvements so as long as it was made from the "master" and not the DVD.

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  3. Just an update, I downloaded 2 cartoons I have on DVD. One TMNT and one Super Mario. I stripped the DRM so I can have a better look, though wasn't vital.

    Both use the same bit depth and Chromo 4:2:0 & 8 bits.

    Resolution was also equivalent (640x480 Square) vs. 720x480 DVD. MPEG 4 h264 2mps VS. MPEG2 5mps also about equivalent, though 5mps is actually less the equivalent would be more around 8.

    Looking at both the major difference was the DVD is 29.97 Interlaced and the iTunes m4v was 23.97 progressive.

    The DVD color was not as good and I can see compression artifacts.

    Botton line is DVD is made for old CRTs and iTunes is progressive and made for new digital monitors and PCs.

    As for TMNT and SMB iTunes won by a lot, much better colors and 23.97 progressive frames. Also the AAC audio far surpassed the *crappy* joint channel AC3.

    My vote for these are iTunes, but obviously source of the studios is going to vary but DVD is IMO an out-dated format made for old interlaced TVs.


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    Replies
    1. Thanks a ton for the analysis. I haven't gone back to this issue since I originally posted this and won't be likely to anytime soon. But your comments are most welcome.

      I think my personal conclusion here is that though iTunes by using MP4 and progressive video and H264 is more often going to be better quality, when dealing with older video sources one cannot be sure.

      Neither iTunes nor the Amazon DVD of the Hey Arnold! series were from remastered sources. The DVD video was about 3.6 times larger than the H264 in this case. While H264 is clearly a better algorithm, in this case it was a close match and I think the colors on the DVD of Hey Arnold! were slightly better than the iTunes episode. Personal taste there perhaps.

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