Mobile Video: Working with MPEG-4 Clips on Mobile Phones
Pages: 1, 2, 3, 4

3GPP Formats

When you send a clip (or photo) by email over the Verizon Wireless network, it arrives as a message sent from your number via the Verizon portal, vzwpix.com, with the file as an attachment. The file has a .3g2 extension, for 3GPP version 2. However, since this is a relatively new format, your existing computer and video applications may not know what to do with this file.

The 3rd Generation Partnership Project (3GPP) is a collaboration of international telecommunications standards bodies, focused on 3G (3rd Generation) technical standards for the GSM (Global System for Mobile) cellular communications technology, which is especially prevalent in Europe, and used by Cingular and T-Mobile in the U.S.

A second group, the 3rd Generation Partnership Project 2 (3GPP2), is a collaboration of North American and Asian standards bodies based in Arlington, Virginia. 3GPP2 is developing 3G specifications based on the CDMA (Code Division Multiple Access) technology, used by Sprint and Verizon Wireless in the U.S.

3GPP and 3GPP2 logos

The resulting specs are closely related, with both groups continuing to work in parallel. Their main focus is combining and extracting from existing technologies like MPEG-4 to define common, interoperable subsets that can be supported across the industry. Since these are technical collaborations (and not patent pooling groups), the specifications are freely available for downloading, although they mostly consist of references to other published standards (see www.3gpp.org/specs/specs.htm, and www.3gpp2.org/Public_html/specs).

For example, 3GPP technical specification TS 26.140 defines media formats and codecs for Multimedia Messaging Service (MMS), with reference to 59 other supporting documents. The base supported 3GPP video and audio formats are:

• Video codecs
  • H.263 Profile 3: Targeted to videoconferencing
  • MPEG-4 Visual Simple Profile: Basic MPEG-4
  • H.264 (AVC) Baseline Profile: Enhanced MPEG-4 (Advanced Video Coding)
• Audio codecs
  • AMR (Adaptive Multi-Rate): For speech
  • Extended AMR-WB (AMR wideband): For better speech quality
  • Enhanced aacPlus (Advanced Audio Coding): Enhanced with MPEG-4

In comparison, the sample 3GPP2 files use MPEG-4 video with Qualcomm QCELP (Qualcomm Code Excited Linear Predictive) audio encoding. QuickTime Player Pro provides profiles for creating both 3GPP and 3GPP2 format files with these codecs.

3GPP Playback in QuickTime Player

The easiest approach for playing 3GPP files is to use Apple's QuickTime Player, bundled on the Macintosh and available as a free download for Windows. Apple has worked hard to support and promoting MPEG-4 in QuickTime 6 and beyond, and added support for 3GPP in QuickTime 6.5.

QuickTime Player error trying to play a .3g2 video clip from the LG VX7000

I've used the new preview release of QuickTime Player 7 for Windows to work with these files, but they also work in version 6.5. To support these formats, make sure you update to at least version 6.5.1 (use Help > Update Existing Software). In Windows Explorer, the type for .3g2 files should then be reported as "3GPP Movie Importer." (Note that auto-updating the Player may not download the 3GP support, so make sure it is installed using Edit > Preferences > QuickTime Preferences > Update Check > Update and Install Additional QuickTime Software.)

As promised, both QuickTime Player versions 6.5 and 7 were happy to open and play the .3g2 files from the Samsung SCH-a890 and Motorola V710. But they rejected the LG VX7000 files, reporting error -2041, "invalid sample description."

The next step was experimenting with renaming the working files to other possible file types: both players could still play the file when the extension was changed to .3gp--but version 6.5 rejected .3gpp as "not a file that QuickTime understands," while the newer version 7 played the file fine. Trying the more generic types did not make QuickTime happy: in version 7, renaming to .mp4 was rejected with "unknown error," and .mov was understandably identified as "not a movie file." Version 6.5 was less happy, and just failed to launch the .mov file without further comment.

Movie Info properties displayed by QuickTime Player for a 3G2 file from the Samsung SCH-a890 mobile phone

The same tests with the problematic LG VX7000 files produced an interesting workaround. All the formats caused an "invalid sample description" error, except .mov--which played fine in both versions 6.5 and 7. Go figure.

Interestingly, the QuickTime Player's Movie Info dialog reports the same format for all these files, so the problem here is likely to be inconsistent implementations of the metadata stored in the file headers:

Video format

MPEG-4 Video, 176 by 144, millions (of colors)

Audio format

Qualcomm QCELP, Mono, 8000 Hz

Frame rate

15 fps

File size

Approx. 170-180 KB

File data rate

Approx. 11.3 KB/sec

Stream data rates

Video, approx. 9.8 KB/sec; Audio, approx. 1.7 KB/sec

Unfortunately, we can expect these kinds of idiosyncrasies when working with "standard" files created by different products. Slight differences in the interpretation of standards, even for unneeded or redundant header information in files, can cause confusion when trying to process them.