FFmpeg Media Encoder – a set of free open source libraries that allow you to record, convert and transfer digital audio and video recordings in various formats. It includes libavcodec, an audio and video encoding and decoding library, and libavformat, a library for multiplexing and demultiplexing into a media container. The name comes from the name of the expert group MPEG and FF, meaning fast forward. (more)
FFmpeg is already built into the program and does not require downloading additional codecs.
Conversion takes place directly on the device (Internet is not required), and the conversion speed depends on the speed of the device processor.
Supports: MPEG4, h264, mp3, 3gp, aac, ogg (vorbis and theora) and many other formats (the list can be found in the program itself). Optimized for ARMv6 (vfp) and ARMv7 (cortex-a8)
Requirements: Android 1.6+ and ARMv6 + VFP processor or higher
Built-in: FFmpeg v0.10 + libx264 + libmp3lame + libvorbis + libtheora + libfaac