FFmpeg is a complete, cross-platform solution to record, convert and stream audio and video. It includes libavcodec - the leading audio/video codec library.
This build is not mine, I found it on internet, but I wanted to share it because is very complete, so just Download ffmpeg now. This build is perfect to encode/decode video from mobiles. You can decode MP4 and 3GPP very easy.
This compilation is done using GCC 4.3.0 20080305 / MinGW 20080502 for Win32. The GCC-built archives of statically-linkable external libraries used in this compilation are available for download at Komeil’s SkyDrive FFmpeg libraries trunk. Also you can find direct download links to each static library in “Build Version” column of “External Libraries” table below. Once downloaded successfully, you need to extract them right into your “MinGW” folder, since the CAB archives include LIB (containing .a library files) and INCLUDE (containing .h header files) directories fittingly. Please note FFmpeg is a stand-alone portable executable, and these libraries are provided for experimentalists interested in compiling FFmpeg by themselves.
Configuration: --enable-memalign-hack --extra-cflags=-fno-common --enable-static --disable-shared --disable-debug --enable-gpl --enable-nonfree --enable-avfilter --enable-avfilter-lavf --enable-avisynth --enable-postproc --enable-pthreads --enable-libamr-nb --enable-libamr-wb --enable-libgsm --enable-libfaac --enable-libfaad --enable-libmp3lame --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libx264 --enable-libxvid
Supported File Formats
This is the list of all media formats FFmpeg SVN-r17988-Komeil can decode from and/or encode to:
| Name | Description | Decode | Encode |
| 3g2 | 3GP2 format | X | |
| 3gp | 3GP format | X | |
| 4xm | 4X Technologies format | X | |
| IFF | IFF format | X | |
| ISS | Funcom ISS format | X | |
| MTV | MTV format | X | |
| RoQ | raw id RoQ format | X | X |
| aac | raw ADTS AAC | X | |
| ac3 | raw AC-3 | X | X |
| adts | ADTS AAC | X | |
| aiff | Audio IFF | X | X |
| alaw | PCM A-law format | X | X |
| amr | 3GPP AMR file format | X | X |
| apc | CRYO APC format | X | |
| ape | Monkey’s Audio | X | |
| asf | ASF format | X | X |
| asf_stream | ASF format | X | |
| ass | SSA/SS format | X | X |
| au | SUN AU format | X | X |
| avi | AVI format | X | X |
| avm2 | Flash 9 (AVM2) format | X | |
| avs | AVISynt | X | |
| bethsoftvid | Bethesda Softworks VID format | X | |
| bfi | Brute Force & Ignorance | X | |
| c93 | Interplay C93 | X | |
| cavsvideo | raw Chinese AVS video | X | |
| crc | CRC testing format | X | |
| daud | D-Cinema audio format | X | X |
| dirac | raw Dirac | X | X |
| dnxhd | raw DNxHD (SMPTE VC-3) | X | X |
| dsicin | Delphine Software International CIN format | X | |
| dts | raw DTS | X | X |
| dv | DV video format | X | X |
| dvd | MPEG-2 PS format (DVD VOB) | X | |
| dxa | DXA | X | |
| ea | Electronic Ars Multimedia Format | X | |
| ea_cdata | Electronic Arts cdata | X | |
| eac3 | raw E-AC-3 | X | X |
| f32be | PCM 32 bit floating-point big-endian format | X | X |
| f32le | PCM 32 bit floating-point little-endian format | X | X |
| f64be | PCM 64 bit floating-point big-endian format | X | X |
| f64le | PCM 64 bit floating-point little-endian format | X | X |
| ffm | FFM (FFserver live feed) format | X | X |
| film_cpk | Sega FILM/CPK format | X | |
| flac | raw FLAC | X | X |
| flic | FLI/FLC/FLX animation format | X | |
| flv | FLV format | X | X |
| framecrc | framecrc testing format | X | |
| gif | GIF Animation | X | |
| gsm | raw GSM | X | |
| gx | GXF format | X | X |
| h261 | raw H.261 | X | X |
| h263 | raw H.263 | X | X |
| h264 | raw H.264 video format | X | X |
| idcin | id Cinematic format | X | |
| image2 | image2 sequence | X | X |
| image2pipe | piped image2 sequence | X | X |
| ingenient | raw Ingenient MJPEG | X | |
| ipmovie | Interplay MVE format | X | |
| ipod | iPod H.264 MP4 format | X | |
| lmlm4 | lmlm4 raw format | X | |
| m4v | raw MPEG-4 video format | X | X |
| matroska | Matroska file format | X | X |
| mjpeg | raw MJPEG video | X | X |
| mlp | raw MLP | X | |
| mm | American Laser Games MM format | X | |
| mmf | Yamaha SMAF | X | X |
| mov | MOV format | X | |
| mov,mp4,m4a,3gp,3g2,mj2 | QuickTime/MPEG-4/Motion JPEG 2000 format | X | |
| mp2 | MPEG udio layer 2 | X | |
| mp3 | MPEG audio layer 3 | X | X |
| mp4 | MP4 format | X | |
| mpc | Musepack | X | |
| mpc8 | Musepack SV8 | X | |
| mpeg | MPEG-1 System forma | X | X |
| mpeg1video | raw MPEG-1 video | X | |
| mpeg2video | raw MPEG-2 video | X | |
| mpegts | MPEG-2 transport stream format | X | X |
| mpetsraw | MPEG-2 raw transport stream format | X | |
| mpegvideo | raw MPEG video | X | |
| mpjpeg | MIME multipart JPEG format | X | |
| msnwctcp | MSN TCP Webcam stream | X | |
| mulaw | PCM mu-law format | X | X |
| mvi | Motion Pixels VI format | X | |
| mxf | Material eXchange Format | X | X |
| mxf_d10 | Material eXchange Format, D-10 Mapping | X | |
| nc | NC camera feed format | X | |
| nsv | Nullsoft Streaming Video | X | |
| null | raw null video format | X | |
| nut | NUT format | X | X |
| nuv | NuppelVideo format | X | |
| ogg | Ogg | X | X |
| oma | Sony OpenMG audio | X | |
| psp | PSP MP4 format | X | |
| psxstr | Sony Playstation STR format | X | |
| pva | TechnoTrend PVA file and stream format | X | |
| r3d | REDCODE R3D format | X | |
| rawvideo | raw video format | X | X |
| rcv | VC-1 test bitstream | X | |
| redir | Redirector format | X | |
| rl2 | RL2 format | X | |
| rm | RealMedia format | X | X |
| rpl | RPL/ARMovie format | X | |
| rt | RTP output format | X | |
| rtsp | RTSP input format | X | |
| s16be | PCM signed 16 bit big-endian format | X | X |
| s16le | PCM signed 16 bit little-endian format | X | X |
| s24be | CM signed 24 bit big-endian format | X | X |
| s24le | PCM signed 24 bit little-endian format | X | X |
| s32be | PCM signed 32 bit big-endian format | X | X |
| s32le | PCM signed 32 bit little-endian format | X | X |
| s8 | PCM signed 8 bit format | X | X |
| sdp | SDP | X | |
| shn | raw Shorten | X | |
| siff | Beam Software SIFF | X | |
| smk | Smacker video | X | |
| sol | Sierra SOL format | X | |
| svcd | MPEG-2 PS format (VOB) | X | |
| swf | Flash format | X | X |
| thp | THP | X | |
| tiertexseq | Tiertex Limited SEQ format | X | |
| tta | True Audio | X | |
| txd | Renderware TeXture Dictioary | X | |
| u16be | PCM unsigned 16 bit big-endian format | X | X |
| u16le | PCM unsigned 16 bit little-endian format | X | X |
| u24be | PCM unsigned 24 bit big-endian format | X | X |
| u24le | PCM unsigned 24 bit little-endian format | X | X |
| u32be | PCM unsigned 32 bit big-endian format | X | X |
| u32le | PCM unsigned 32 bit little-endian format | X | X |
| u8 | PCM unsigned 8 bit format | X | X |
| vc1 | raw VC-1 | X | |
| vc1test | VC-1 test bitstream format | X | |
| vcd | MPEG-1 System format (VCD) | X | |
| vfwcap | VFW video capture | X | |
| vmd | Sierra VMD format | X | |
| vob | MPEG-2 PS format (VOB) | X | |
| voc | Creative Voice file format | X | X |
| vqf | Nippon Telegraph and elephone Corporation (NTT) TwinVQ | X | |
| wav | WAV format | X | X |
| wc3movie | Wing Commander III movie format | X | |
| wsaud | Westwood Studios audio format | X | |
| wsvqa | Westwood Studios VQA format | X | |
| wv | WavPack | X | |
| xa | Maxis XA File Format | X | |
| yuv4mpegpipe | YUV4MPEG pipe format | X | X |
Happy decoding/encoding!

Hi David
Thank you for the brillient post, i had been searching alot to convert amr to mp3 programmetically…
The info given above worked for me…!!!
Thank you for sharing knowledge !!!!
Con el Cydia en el iPhone podes instalar el FFmpeg con dos “taps”, y funciona de maravilla en el Terminal.