Primer - Movie Formats And Conversion

Movie formats and conversion: What you can watch on your Apple devices all comes down to formats.

The more complex the content, the greater are the number of different docu­ment formats. Words, particularly text, are now contained in no more than a handful of major formats, such as plain text, Word .doc and Acrobat .pdf, with ample varia­tions and versions of each. Still images are more diverse again, and when they become moving images with the addition of sound, the range seems almost infinite.

Apple’s refusal to support the Flash format in iOS means you can’t watch some internet content on your iPad - though Flash-only content is becoming rare.

The easy way of watching movies on your Mac, iPad or Apple TV is using the iTunes Store, where they have guaranteed compatibility so you should never have to worry about their format. When you want to watch footage that you’ve shot yourself or downloaded from the internet, however, you can quickly become confused and frustrated when you discover that it won’t transfer or play. Before struggling to convert it, you need a working knowledge of the different formats in which movies can be presented. Critical factors include resolution, frame rate, compression and container format.

Resolution is the most basic property of movies - for example, the optimum 1,920 x 1,080 used in HD video determines the aspect ratio, now generally widescreen at 16:9. There are still plenty of items shot in standard-definition (SD) TV, which has a 4:3 ratio. Most movie players give good flexibil­ity and will re-scale to accommodate a wide range of resolutions. However, a mismatched aspect ratio will remain a compromise: wide­screen movies played on a 4:3 or similar screen are best viewed in ‘letterbox’, but that wastes the upper and lower parts of screen. Old 4:3 video, from older TV shows, similarly wastes the sides of a widescreen display, but that’s usually more acceptable given the typically low resolution of the image.

Get Flashy: The free Firefox plug-in Flash Video Downloader needs to be primed by playing the movie you want to download, and can convert it, too

Images are most easily scaled on the fly to round multiples of resolution, so display­ing a movie in 960 x 540 on an HD screen is readily achieved by doubling, but the result­ing image is then visibly coarse. Note that early HD movies based on 720 pixels aren’t a round fraction of current 1080 HD formats, so have to be scaled by the sophisticated hardware of a fast graphics card.

The next fundamental property is the frame rate, such as 23.976 or 24 fields per second for progressive (p) formats popular in cinema movies, and 25,29.97 or 59.94 for interlaced (i) versions for broadcast. These must exceed the flicker fusion frequency, a threshold in visual perception that’s nor­mally around 16 frames per second; however, given the right lighting conditions and con­tent, many of us can see flicker at higher frame rates.

Interlacing is a trick derived from broad­cast TV, refreshing only alternate lines making up half fields - at 60 fields/sec, each line is only refreshed 30 times per second, making rapid motion appear smoother. Some prefer de-interlacing to give a cin­ematic movie ‘look’: in an ideal system, that would keep the original frame rate, display­ing each frame twice, at 48-60 frames per sec. For once, US standards based on 60Hz are superior to those in Europe, which are based on 50Hz, but graphics cards and dis­plays have become remarkably catholic in their abilities to cope.

Compression format is far more impor­tant in determining what you can watch. Raw, uncompressed video demands massive amounts of storage space, so your player needs to be able to decode both video and audio streams in real time while you watch the movie. SD DVD uses the MPEG-2 stand­ard, while HD, including Blu-ray, opts for the much more efficient MPEG-4 and its range of compression methods, including H.264. With ample fast processor power, it’s pos­sible to perform this decoding in software, but that will result in jittery playback if the processor cores are loaded with other com­peting processes. This is where hardware decompression comes into its own, such as with H.264 in graphics cards.

Movies can’t have a simple linear data format, as they consist of multiple tracks, each of which can be video, audio or other content. The overall scheme within which their data are held is their container format, and includes QuickTime, Flash, RealVideo, WMV and a couple of dozen others. Even if all the above are right, if a movie is in a closed or inaccessible container format, you will be unable to play it.

Apple’s QuickTime movie containers typically have filename extensions of .mov or .qt, are almost identical to the open MPEG-4 standard, and are well supported in OS X and iOS. Neither should you have any difficul­ties with the MPEG family, which includes both the original MPEG (.mpeg extension) using MPEG-2 or MPEG-1 compression, and the newer MP4 (.mp4) with MPEG-4 using H.264 compression and more.

Play time: The free Flip4Mac codec plug-in lets you play WMV files in QuickTime Player, but doesn’t convert them, for which you must pay.

Flash movies with the .flv extension have been the default container format for several major sites, including YouTube and the BBC. They can also be contained within any SWF file to provide movie content. Previously, their compression methods were unusual, including Sorenson Spark and VP6, but more recently H.264 has been added, although that should be almost confined to .f4v files.

It’s normally intended that Flash con­tent is played only using Adobe Flash Player and its browser plug-in, which aren’t sup­ported on iOS devices, but many third-party tools are now available to work with them. A common problem is saving local copies of Flash movies, a feature that isn’t normally permitted by Flash Player. The simplest solution at present is to use Firefox with its free Flash Video Downloader plug-in.

RMVB or RealVideo format (.rv and ,rm files) has been quite widely used, and is dependent on the commercial RealPlayer and plug-ins from RealNetworks. These can contain a range of different video compres­sion formats, as well as its own proprietary scheme. Its engine is now available in open source as the Helix project and promises to open access to these movies that have otherwise been locked in to their player. DivX is another proprietary container format, which is essentially built around its proprietary compression format, but is now accessible within the MPEG-4 standard.

Although normally assumed to be a container format, Windows Media Video (.wmv) is actually the name of the compres­sion format most commonly presented in an Advanced Systems Format (ASF) con­tainer. The standard tool for working with these on OS X is the commercial Flip4Mac WMV, although widespread use of the Windows Media DRM can make access fraught. ASF/WMV was intended to replace the ancient Audio Video Interleave (AVI, .avi files) format, which had become such a ragbag that it was a feast of incompatibili­ties. AVI files can contain movies that are not only inaccessible in OS X, but can’t even be opened in Windows any more.

Microsoft’s latest platform, Silverlight, isn’t actually a container format, but is equivalent to Adobe Flash as a rich media application framework, which supports legacy compression formats such as WMV, as well as currently popular ones such as H.264. It’s supported in a proprietary plug-in for OS X, but not on iOS, as it’s offered as a competitive feature on Windows Phone.

Saving from Flash

Of all the container formats, Flash is often the most frustrating, as it forces you to view movies online, but blocks you from saving them locally for future viewing. Since Flash first became popu­lar, there has been a cat-and-mouse game played out between Adobe and developers of third-party tools that have tried to capture Flash movies in accessible formats.

Inside info: At its most basic, Metadata Hootenanny gives you information about the encoding of tracks in any QuickTime movie.

At present, the easiest and most reliable is the free Flash Video Downloader plug-in for Firefox. Point this browser at the page containing the Flash movie that you want to down­load, then click on the tool to select the movie from those available on that page and download it. With many sites offering Flash movies putting multiple items on each page, you need to start playing the movie that you want, in order to identify it and start down­loading. The tool can also be brought up as a floating pane rather than just a pop-up menu to help select and con­vert the download.

Once you have a Flash or other movie in QuickTime form, you need to discover the compression formats used and other details. An excellent free tool for that, far superior to Apple’s now severely stunted QuickTime Player application, is Metadata Hootenanny, alias MetaHoot, free from applesolutions.com/bantha/MH.html. This has greater capabilities and features, as it allows you to edit the metadata stored in each movie, which can be put to good use when building a movie library and accessing it from iOS devices.

Opening a movie with MetaHoot lets you inspect its constituent tracks and chapters to see their encoding, so that you can transcode any that need it. There are also tools to allow you to insert additional material, and its online quick-start guide walks you through creating a complete DVD- style sprite-rich menu and scripts.

Conversion and playback

Having got your movie onto your Mac and identified the compression for­mats used, you next need to prepare it for viewing on your iPad or other device. Here, the best all-round conversion tool is HandBrake, free from handbrake, fr, which can perform most conversions provided that it can decompress the input formats. It can’t remove DRM protection such as that found in most DVD and Blu-ray products, nor that in WMV files; indeed, it can’t open proprietary formats such as ASF/WMV. HandBrake offers a convenient range of presets for iPads, Apple TV and other popular platforms that should make your task simpler. If you have many movies to convert, it can run in the background, and a batch tool is available.

Convert operation: With its useful suite of presets, HandBrake sets the standard for movie conversion, although it can’t read proprietary formats.

Transcoding video should be undertaken with caution. Almost all compres­sion formats are lossy; just as repeatedly recompressing still images leads to degradation in quality, transcoding will have adverse effects on a movie. Try to do this no more than once, and select a good compromise between compactness and quality. Keep the master version of the movie, so that if you need to per­form more than one transcoding, you can work from the original material rather than a transcoded derivative.

ASF/WMV and other proprietary formats will need a specialist conversion application, such as Flip4Mac Player Pro (from telestream.net/flip4mac-wmv/ wmv-player-pro.htm) or any of the clutch of competitors available in the App Store. Although the free Flip4Mac plug-in allows you to put and play WMV within a QuickTime container, there’s no reliable free conversion tool. There are many that claim to support these more difficult formats, but confirm that they work before committing to them: some have good reputations, such as iVL (southpolesoftware.com/iVI/iVI.php), but others are of little use.