3G2 to SPX Converter

3G2 (3GPP2 file format) is a multimedia container developed by the 3rd Generation Partnership Project 2 for use on CDMA2000 mobile networks. Built on the ISO base media file format (MPEG-4 Part 12), it stores video encoded with H.263 or MPEG-4 Visual alongside audio in AMR, EVRC, or AAC codecs. The specification was first published in December 2003 to provide a standardized way for CDMA-based phones and networks to handle multimedia messaging and video playback. 3G2 files are engineered for extremely low-bandwidth conditions, achieving playable video quality at bit rates as low as 30-60 kbps. This makes the format especially efficient for mobile video capture on devices with limited processing power and storage. The container supports multiple tracks, timed text for subtitles, and embedded metadata. One significant benefit is near-universal compatibility with CDMA handsets from the mid-2000s era, ensuring reliable playback across a wide range of mobile devices. Though newer formats like MP4 have superseded 3G2 for most purposes, it remains useful for working with legacy mobile content and for situations where minimal file size is the primary concern.

Speex is an open-source audio codec purpose-built for speech compression, developed by Jean-Marc Valin under the Xiph.Org Foundation. First released in October 2002, it targets voice-over-IP, conferencing, and any scenario where spoken word needs to travel efficiently over a network. SPX files wrap Speex-encoded audio inside an Ogg container, pairing the codec's speech optimization with Ogg's streaming capabilities. Three sampling rates are supported — narrowband at 8 kHz, wideband at 16 kHz, and ultra-wideband at 32 kHz — along with variable bitrate encoding that adapts in real time to speech complexity. A standout advantage is its patent-free, BSD-licensed nature, which allowed developers to embed it freely in both commercial and open-source products. Speex also bundles acoustic echo cancellation, noise suppression, and automatic gain control, features that rival codecs typically delegate to external libraries. Although its creators officially recommend Opus) as a successor since 2012, Speex remains deployed in legacy VoIP systems, archived recordings, and embedded devices where its lightweight decoder footprint is still valued.