我该如何找到这个FFmpeg错误代码的含义？

Question

我正在使用函数avcodec_decode_video2。在流中进行编码更改时，它返回-1094995529。文档只说明：

发生错误会返回负值，否则将返回使用的字节数，如果无法解压缩帧，则返回零。

但是似乎没有返回代码的枚举或其他形式的文档。该错误是什么意思，我如何确定一般情况下的错误？

- Asik

Answer 1

来自ffmpeg（avutil中的error.h）的错误代码： http://ffmpeg.org/doxygen/trunk/error_8h_source.html

事实证明，您指定的值为：

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

-1094995529变成了-0x41444E49，当你查看这些字母时，在ACSII中，0x41 = 'A'，0x44 = 'D'，0x4E = 'N'，0x49 = 'I'。由于宏等的原因，它们被反转了，所以ADNI变成了INDA，可以从#define片段中看到，这是AVERROR_INVALIDDATA定义的FFERRTAG（'I'，'N'，'D'，'A'）。

其余的错误代码在那个文件中，我将它们以下面的形式粘贴在下面：

#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')

- LawfulEvil

Answer 2

错误信息提到的是 POSIX 相关问题：

在 libavcodec\avcodec.h 文件中

#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. */

这是您可能遇到的所有错误的完整集合。只需在代码中检查返回值与它们中的所有值进行比较即可。

- Boris Ivanov

---

谢谢。我找到了这个，但是它们都基于errno.h，其范围为1-131。我不明白为什么会返回如此大的值-1094995529。 - Asik

在上面的代码中，你可以看到对否定的使用。即使如此，我们的数字看起来很奇怪。那么为什么不直接写成：如果 (retcode == AVERROR(EINVAL) ){ printf("未知错误"); } - Boris Ivanov