How can I find out what this ffmpeg error code means?

Error codes from ffmpeg (error.h from avutil) :http://ffmpeg.org/doxygen/trunk/error_8h_source.html

It turns out the value you specified is :

#define AVERROR_INVALIDDATA        FFERRTAG( 'I','N','D','A')

The -1094995529 becomes -0x41444E49 and when you look at those letters, in ACSII, 0x41 = 'A', 0x44 = 'D', 0x4E = 'N, and 0x49 = 'I'. Due to the macro/etc things are reversed, so ADNI becomes INDA, which you can see from the #define snippet, is the AVERROR_INVALIDDATA defined FFERRTAG( 'I','N','D','A').

The rest of the error codes are in that file and I've pasted them below here :

#define AVERROR_BSF_NOT_FOUND      FFERRTAG(0xF8,'B','S','F') ///< Bitstream filter not found#define AVERROR_BUG                FFERRTAG( 'B','U','G','!') ///< Internal bug, also see AVERROR_BUG2#define AVERROR_BUFFER_TOO_SMALL   FFERRTAG( 'B','U','F','S') ///< Buffer too small#define AVERROR_DECODER_NOT_FOUND  FFERRTAG(0xF8,'D','E','C') ///< Decoder not found#define AVERROR_DEMUXER_NOT_FOUND  FFERRTAG(0xF8,'D','E','M') ///< Demuxer not found#define AVERROR_ENCODER_NOT_FOUND  FFERRTAG(0xF8,'E','N','C') ///< Encoder not found#define AVERROR_EOF                FFERRTAG( 'E','O','F',' ') ///< End of file#define AVERROR_EXIT               FFERRTAG( 'E','X','I','T') ///< Immediate exit was requested; the called function should not be restarted#define AVERROR_EXTERNAL           FFERRTAG( 'E','X','T',' ') ///< Generic error in an external library#define AVERROR_FILTER_NOT_FOUND   FFERRTAG(0xF8,'F','I','L') ///< Filter not found#define AVERROR_INVALIDDATA        FFERRTAG( 'I','N','D','A') ///< Invalid data found when processing input#define AVERROR_MUXER_NOT_FOUND    FFERRTAG(0xF8,'M','U','X') ///< Muxer not found#define AVERROR_OPTION_NOT_FOUND   FFERRTAG(0xF8,'O','P','T') ///< Option not found#define AVERROR_PATCHWELCOME       FFERRTAG( 'P','A','W','E') ///< Not yet implemented in FFmpeg, patches welcome#define AVERROR_PROTOCOL_NOT_FOUND FFERRTAG(0xF8,'P','R','O') ///< Protocol not found#define AVERROR_STREAM_NOT_FOUND   FFERRTAG(0xF8,'S','T','R') ///< Stream not found#define AVERROR_BUG2               FFERRTAG( 'B','U','G',' ')#define AVERROR_UNKNOWN            FFERRTAG( 'U','N','K','N') ///< Unknown error, typically from an external library#define AVERROR_EXPERIMENTAL       (-0x2bb2afa8) ///< Requested feature is flagged experimental. Set strict_std_compliance if you really want to use it.#define AVERROR_INPUT_CHANGED      (-0x636e6701) ///< Input changed between calls. Reconfiguration is required. (can be OR-ed with AVERROR_OUTPUT_CHANGED)#define AVERROR_OUTPUT_CHANGED     (-0x636e6702) ///< Output changed between calls. Reconfiguration is required. (can be OR-ed with AVERROR_INPUT_CHANGED)#define AVERROR_HTTP_BAD_REQUEST   FFERRTAG(0xF8,'4','0','0')#define AVERROR_HTTP_UNAUTHORIZED  FFERRTAG(0xF8,'4','0','1')#define AVERROR_HTTP_FORBIDDEN     FFERRTAG(0xF8,'4','0','3')#define AVERROR_HTTP_NOT_FOUND     FFERRTAG(0xF8,'4','0','4')#define AVERROR_HTTP_OTHER_4XX     FFERRTAG(0xF8,'4','X','X')#define AVERROR_HTTP_SERVER_ERROR  FFERRTAG(0xF8,'5','X','X')

Errors mentioned are POSIX related:

in file libavcodec\avcodec.h

#include <errno.h>#if EINVAL > 0#define AVERROR(e) (-(e)) /**< Returns a negative error code from a POSIX error code, to return from library functions. */#define AVUNERROR(e) (-(e)) /**< Returns a POSIX error code from a library function error return value. */#else/* Some platforms have E* and errno already negated. */#define AVERROR(e) (e)#define AVUNERROR(e) (e)#endif#define AVERROR_UNKNOWN     AVERROR(EINVAL)  /**< unknown error */#define AVERROR_IO          AVERROR(EIO)     /**< I/O error */#define AVERROR_NUMEXPECTED AVERROR(EDOM)    /**< Number syntax expected in filename. */#define AVERROR_INVALIDDATA AVERROR(EINVAL)  /**< invalid data found */#define AVERROR_NOMEM       AVERROR(ENOMEM)  /**< not enough memory */#define AVERROR_NOFMT       AVERROR(EILSEQ)  /**< unknown format */#define AVERROR_NOTSUPP     AVERROR(ENOSYS)  /**< Operation not supported. */#define AVERROR_NOENT       AVERROR(ENOENT)  /**< No such file or directory. */#define AVERROR_EOF         AVERROR(EPIPE)   /**< End of file. */#define AVERROR_PATCHWELCOME    -MKTAG('P','A','W','E') /**< Not yet implemented in FFmpeg. Patches welcome. */

This is full set of Errors you can meet. Simply inside your code check return value against all of them.