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White Paper: Media Container File Formats

Michael Brown — Thu, 24 Sep 2009 14:30:42 -0500

Meet the digital equivalent of Tupperware for your music and video files

When can a file encapsulate more than one type of data? When it’s a metafile, wrapper, or container file. You might think of a container file as a package or envelope in which other files are housed. Zip files, which can contain documents, photos, videos, software programs, and many other types of files, are one type of container that you encounter frequently.

We’ll limit our discussion here to media container formats. A pure container file specifies how the data is stored, but it doesn’t necessarily know how it was compressed or encoded or even what is required to play back those files. This can lead to confusion when dealing with container files wrapped around media because there’s a chance that the media player you’re using is capable of opening the container but not equipped with the algorithm required to decode the files inside. Although a container can theoretically hold any type of data, most are optimized during development to wrap around particular data groups, e.g., digital audio for music; static images for digital photographs; or digital video interleaved with digital audio, plus subtitles, closed-caption information, and chapter data for movies. Container formats that support video also include the information required to synchronize the various data streams in the file during playback.

The MP4 container, which is based on Apple's QuickTime technology, encapsulates audio, video, and synchronization information in a series of packages within packages.

Container files store data in chunks, packets, or segments; three terms that describe essentially the same concept. A chunk’s primary content is known as its payload, and most container formats arrange their chunks in sequence, with a file header at the beginning of each chunk that describes the type of data contained in the payload. This arrangement makes it easier to recover lost chunks in the event of file corruption or dropped frames.

Common Media Containers

WAV is a common example of a container format that’s used exclusively for audio on the Windows platform, although the container is also compatible with the Linux and Macintosh operating systems. WAV containers typically host uncompressed linear pulse code modulation (LPCM) audio files encoded in RIFF (Resource Interchange File Format). When you rip a CD to your hard drive, the file is converted from the Red Book audio format and saved as a WAV file on your hard drive, although most people then convert that file to another, less storage-intensive format using a lossy code such as MP3, or a lossless one such as FLAC.

If you’ve ever ripped a movie from a DVD (or just examined the directory structure on a DVD), you’ve encountered VOB files (the acronym stands for Video Object). VOB files are containers that house a DVD’s digital video and audio streams, plus menus and data streams such as subtitles. There is typically one VOB file for each title on the disc, although this is not a requirement. VOB files are in turn based on the MPEG Program Stream, a container format that multiplexes packetized digital audio, video, and data streams (these are individually known as elementary streams). Elementary streams are packetized by dividing the stream into sequential bytes and encapsulating them in packet headers.

Movies on Blu-ray discs, on the other hand, utilize a container based on the MPEG Transport Stream. Just like MPEG-PS, MPEG-TS multiplexes packetized digital audio, video, and data streams and synchronizes their output; the key difference is that MPEG-TS supports a mechanism for error correction. MPEG-TS is also used in the U.S. for ATSC digital television broadcasts.

Apple’s QuickTime container (which uses the file extension MOV) can host multiple audio, video, effects, and text tracks (for subtitles). MOV files are unique among media containers in that each track can contain either a digital media stream or a reference to a media stream contained in a separate file. This latter feature renders QuickTime very well-suited to editing because the media doesn’t need to be rewritten after an edit. QuickTime also forms the basis of the MPEG-4 Part 14 container (which uses the file extension MP4). Both MOV and MP4 containers can use the same MPEG-4 codecs, but MP4 is more widely supported because it’s an international standard.

Other popular container formats include AVI (Audio Video Interleave), an aging but ubiquitous Microsoft standard that can contain many types of audiovisual data, including MPEG-4; Ogg, the standard container for audio encoded with the open-source Vorbis codec and video encoded with the open-source Theora codec; and RealMedia, the standard container for RealNetworks’ RealVideo and RealAudio files.

But no discussion of media container formats would be complete without mentioning the Matroska Multimedia Container. This ambitious open-standard and royalty-free file format (its ownership resides in the public domain) can hold an unlimited number of media tracks in a single file. Unlike the other container formats we’ve covered, which are limited to certain types of audio and video files encoded using particular codecs, Matroska containers can harbor audio and video files encoded using virtually any codec (MPEG-4, H.264, MP3, FLAC, WMA, and more—including Dolby TrueHD and DTS-HD, the HD audio formats used on Blu-ray discs). MKV files are used to store video files, MKA files to store audio-only files, and MKS files are used for subtitles. Matroska containers can also support chapter divisions, subtitles, menus, and metadata and tags.

Cowon A3 Portable Multimedia Player

Michael Brown — Wed, 03 Sep 2008 20:00:00 -0500

If you’re willing to look beyond everyone’s favorite fruit company when you shop for a digital media player, you’ll encounter some wildly underrated alternatives. Cowon manufactures more than a few, including the nearly divine A3.

In fact, there’s just one feature that kills our enthusiasm for this chunky player: The joystick you must use to control the player and navigate its user interface.

Pushing the tiny, sturdy stick to the left or right (to skip tracks or navigate menus) is easy enough, as is moving it up and down (to control the volume, for instance); but pushing it in to select a file requires the kind of pinpoint accuracy that’s nearly impossible to achieve with as blunt an instrument as your thumb. The slightest amount of off-axis pressure pushes the stick to the right, left, up, or down, triggering an unintended action.

Navigating the graphic user interface with the thumb stick is a snap—until you want to select a file or initiate playback by pushing down on the stick. In our experience, nine out 10 depressions resulted in an unintended action (such as the selector moving to a different function or target file or folder).

It’s an unfortunate flaw, because the rest of the A3’s feature set is absolutely delicious. The player has a four-inch display boasting resolution of 800x480 pixels (16:9 aspect ratio), for starters. It supports a wide variety of video codecs (DivX 3.11 through DivX 6, XviD, H.264, WMV, MPEG-4—even M-JPEG!), every important non-proprietary audio codec (MP3, AAC, WMA, FLAC, OGG Vorbis, and more), and a broad range of digital photo file formats (JPEG, GIF, PNG, TIF, BMP, and RAW). The A3 also has CSD viewer software that enables it to convert and display documents saved in PDF, DOC, HTML, PPT (PowerPoint), XLS (Excel spreadsheet), and several other formats.

We listened to a wide variety of FLAC-encoded tracks (including Lyle Lovett’s cover of “Bears,” from Step Inside This House) and were very impressed with the A3’s audio fidelity. We used TBI’s Millenia amplifier and Majestic Diamond IR speakers for our playback tests. The screen does a fabulous job of displaying digital photos and video clips, too.

The player has every input and output port you could want: headphone, mic, audio in/out, and video in/out (using a proprietary cable with S- and composite video jacks). There’s a set of built-in stereo speakers, too. We wouldn’t recommend listening to them for very long, but they are convenient. The device can function as a USB host, which means you can plug it straight into your digital camera and offload photos from that device’s storage media.

The A3 is a tad too thick (0.75 inches) and heavy (9.8 ounces) to carry in a shirt pocket for long, but much of that bulk can be attributed to the fact that it’s packing a 1.8-inch 30GB hard drive (higher-priced models with 60- and 80GB drives are also available). A padded carrying case is the only other accessory we can think of that Cowon should consider throwing in the box.

Now if they could just do something about that finicky joystick.

iRiver E100 Digital Media Player

Michael Brown — Mon, 21 Apr 2008 14:18:14 -0500

iRiver’s new E100 digital media player offers a several terrific features, including a MicroSD memory slot, FLAC and OGG support, and the ability to record audio (there’s a built-in mic and a line-level input). Unfortunately, all that goodness is undermined by the device’s many flaws.

Some would argue that FLAC files are too large to use with a 4GB flash player (there's an available 8GB model, too), but sometimes we’d rather carry fewer songs (and change them out more often) than subject our ears to music ripped using a lossy codec. iRiver includes a software utility for transferring files from your PC to the E100, but the software will only recognize the player if it has been formatted in MSC mode (in which case it behaves as an external drive when connected to the PC). Subscription music services such as Rhapsody, however, require the device to be formatted in MTP mode. Since that’s how the player is shipped in the U.S. market, the software is useless for file transfers (unless you reformat the player).

We did use the software to convert some WMV files (the player supports MPEG-4, WMV9, and XVID file formats) to the player’s maximum supported resolution of 320x240, but we weren’t impressed with the results: The video was grainy and exhibited poor contrast, and bright colors—especially yellow—appeared blotchy and badly pixelated. Off-axis viewing was even worse.

When we copied a FLAC file to the device using Vista’s Windows Explorer, the OS served up an error message stating that it would gladly transfer the file to the E100, but that the device wouldn’t be capable of playing it; as it turned out, FLAC files played just fine. We experienced a slightly different problem with tracks we ripped from CD and encoded in MP3 format: This time, the album art we embedded in the tracks showed up, but it was scrambled beyond recognition. When we synced the player to our Rhapsody library, on the other hand, the album art came over without a hitch. Go figure.

Reformatting the player to MSC mode got rid of the error message when transferring FLAC files, but it didn’t solve the problem of the missing album art. In this mode, however, you can’t use the E100 with Rhapsody, nor can you use Windows Media Player 11 (or MediaMonkey ) to sync the player to your PC’s music library.

The E100 has a pair of miniature speakers built into the back of the case, but they sound so tinny that we’d recommend listening to them only if you use the built-in mic to record brief voice memos (verbal shopping lists come to mind); they’re useless for music playback. Listening to the player with a good set of headphones delivers much better results, although nothing better than we’ve heard from any number of other digital media players lately.

You control the player and navigate its menus using a set of five buttons at the bottom of the player—four are the points of the compass points and the fifth is in the center. Drilling down into the nested menus requires lots of button mashing—and just as much to back out again. But there were many times in which the device responded sluggishly to a button click, and a few occasions in which the player didn’t respond at all. Not good.

With so many very strong digital media players on the market, there’s just not much of a reason to give the iRiver E100 a second thought.

Make Bit-Perfect Archives of Your CDs With FLAC

Michael Brown — Thu, 28 Jun 2007 20:02:52 -0500

Audio CDs are susceptible to damage and aging, so it’s a good idea to make archival copies of your collection. We’ll show you how, using the lossless compression algorithm FLAC (Free Lossless Audio Codec).

A lossless encoder compresses digital audio files with absolutely no compromise in fidelity compared to the original. The only drawbacks are large file sizes (though they’re much smaller than WAV files) and scarce support among portable players. On the other hand, FLAC enjoys wide support among audio-streaming boxes.

What You’ll Need

Your audio CD collection
Exact Audio Copy (free)
FLAC (free)
AccurateRip (free)

STEP 1: INSTALL EAC AND FLAC

Exact Audio Copy (EAC) will detect and attempt to auto-configure any optical drives on your system during setup. Check those you wish to use and click Next. Use the “I prefer to have accurate results” option and click Next.

Choose the option “I don’t trust these values…,” drop a clean audio CD in the drive, and click Next. It’s crucial that the drive you rip from has an “accurate stream,” meaning it does not produce “jitter” (if the drive can’t accurately seek a specific sector on the disc, ripped tracks will have audible distortion).

Remove the checkmark next to “Install and configure LAME…” and click Next. Enter an email address and click Next. Choose the Expert option at the final prompt and click Finish. Exit EAC.

Install FLAC, ignoring the Winamp and Nero messages. Leave checkmarks next to all the default options and click Install.

STEP 2: INSTALL ACCURATERIP

Using AccurateRip and EAC’s Test & Copy option will provide an added measure of assurance that your rips are precise and worthy of your archive.

Install AccurateRip and then copy the file accuraterip.dll from C:\program files\illustrate\dbpoweramp to C:\program files\exact audio copy. Put a CD in the drive and relaunch EAC. Click the Configure button and then click OK. Select all tracks and click EAC’s Action menu. Choose Copy Selected Tracks from the drop-down menu; use the uncompressed option.

AccurateRip will compare your results to a database of rips by others and report a confidence level. “Confidence 30,” for example, means your rip is identical to that of 30 other people, so there’s a high probability it’s accurate. Click OK.

STEP 3: CONFIGURE EAC

Click the EAC menu and choose EAC Options. Click the General tab. Leave these options at their defaults but place a checkmark next to “On unknown CDs” and select the option “Automatically access online freedb database.” Click the Tools tab and place checkmarks next to everything except “Create ‘.m3u’ playlist…,” “Do not open external…,” and “Activate beginner mode.”

Click the Filename tab and enter the values %A\%C\%N - %T into Naming Scheme to create a nested directory structure that follows the Artist Name\Album Title\Track Number - Track Title scheme. Check “Use various artist naming scheme” and enter the values Various Artists\%C\%N - %A %T so compilation albums are stored in a “Various Artists” folder broken up by album. Click OK.

Click the EAC menu again and choose Drive Options and Extraction Method. Make sure Secure Mode is selected, with a checkmark next to “Drive has Accurate Stream feature.” Click the Drive tab and check “Spin up drive before extraction.” Leave everything else at default and click OK.

Click the EAC menu once more, choose Compression Options and External Compression. Check “Use external program for compression.” In the drop-down menu “Parameter passing scheme,” select “User Defined Encoder.” Type .flac in the “Use file extension” box.

Click Browse, locate the FLAC executable (flac.exe), select it, and click OK. Enter these characters into “Additional command line options”: -6 -V -T “artist=%a” -T “title=%t” -T “album=%g” -T “date=%y” -T “tracknumber=%n” -T “genre=%m” -T comment=”%e” -T “comment=EAC (Secure Mode)” %s. Bitrate doesn’t matter, but check “Delete WAV after compression” and “Check for external compression return code.”

STEP 4: COMMENCE ARCHIVING

Place the audio CD you wish to archive in the drive. Click the Action menu and choose “Test and Copy Selected Tracks” using the Compressed option this time. This will perform a cyclical redundancy check (CRC) to verify the integrity of your rip. It’s another paranoid step, but we think it’s warranted when producing critical backups. An OK will appear in EAC’s CRC column if the rip was executed successfully. Repeat until you’ve backed up your entire library.