FFMPEG中av_log()函數

函數av_log()

void av_log_default_callback(void* ptr, int level, const char* fmt, va_list vl)
{
    static int print_prefix = 1;
    static int count;
    static char prev[LINE_SZ];
    AVBPrint part[4];
    char line[LINE_SZ];
    static int is_atty;
    int type[2];
    unsigned tint = 0;

    if (level >= 0) {
        tint = level & 0xff00;
        level &= 0xff;
    }

    if (level > av_log_level)
        return;
#if HAVE_PTHREADS
    pthread_mutex_lock(&mutex);
#endif

    format_line(ptr, level, fmt, vl, part, &print_prefix, type);
    snprintf(line, sizeof(line), "%s%s%s%s", part[0].str, part[1].str, part[2].str, part[3].str);

#if HAVE_ISATTY
    if (!is_atty)
        is_atty = isatty(2) ? 1 : -1;
#endif

    if (print_prefix && (flags & AV_LOG_SKIP_REPEATED) && !strcmp(line, prev) &&
        *line && line[strlen(line) - 1] != '\r'){
        count++;
        if (is_atty == 1)
            fprintf(stderr, "    Last message repeated %d times\r", count);
        goto end;
    }
    if (count > 0) {
        fprintf(stderr, "    Last message repeated %d times\n", count);
        count = 0;
    }
    strcpy(prev, line);
    sanitize(part[0].str);
    colored_fputs(type[0], 0, part[0].str);
    sanitize(part[1].str);
    colored_fputs(type[1], 0, part[1].str);
    sanitize(part[2].str);
    colored_fputs(av_clip(level >> 3, 0, NB_LEVELS - 1), tint >> 8, part[2].str);
    sanitize(part[3].str);
    colored_fputs(av_clip(level >> 3, 0, NB_LEVELS - 1), tint >> 8, part[3].str);

#if CONFIG_VALGRIND_BACKTRACE
    if (level <= BACKTRACE_LOGLEVEL)
        VALGRIND_PRINTF_BACKTRACE("%s", "");
#endif
end:
    av_bprint_finalize(part+3, NULL);
#if HAVE_PTHREADS
    pthread_mutex_unlock(&mutex);
#endif
}

static void (*av_log_callback)(void*, int, const char*, va_list) =
    av_log_default_callback;

void av_log(void* avcl, int level, const char *fmt, ...)
{
    AVClass* avc = avcl ? *(AVClass **) avcl : NULL;
    va_list vl;
    va_start(vl, fmt);
    if (avc && avc->version >= (50 << 16 | 15 << 8 | 2) &&
        avc->log_level_offset_offset && level >= AV_LOG_FATAL)
        level += *(int *) (((uint8_t *) avcl) + avc->log_level_offset_offset);
    av_vlog(avcl, level, fmt, vl);
    va_end(vl);
}

void av_vlog(void* avcl, int level, const char *fmt, va_list vl)
{
    void (*log_callback)(void*, int, const char*, va_list) = av_log_callback;
    if (log_callback)
        log_callback(avcl, level, fmt, vl);
}

 

結構體AVBPrint定義

在libavutil/bprint.h，即

#define FF_PAD_STRUCTURE(name, size, ...) \
struct ff_pad_helper_##name { __VA_ARGS__ }; \
typedef struct name { \
    __VA_ARGS__ \
    char reserved_padding[size - sizeof(struct ff_pad_helper_##name)]; \
} name;

/**
 * Buffer to print data progressively
 *
 * The string buffer grows as necessary and is always 0-terminated.
 * The content of the string is never accessed, and thus is
 * encoding-agnostic and can even hold binary data.
 *
 * Small buffers are kept in the structure itself, and thus require no
 * memory allocation at all (unless the contents of the buffer is needed
 * after the structure goes out of scope). This is almost as lightweight as
 * declaring a local "char buf[512]".
 *
 * The length of the string can go beyond the allocated size: the buffer is
 * then truncated, but the functions still keep account of the actual total
 * length.
 *
 * In other words, buf->len can be greater than buf->size and records the
 * total length of what would have been to the buffer if there had been
 * enough memory.
 *
 * Append operations do not need to be tested for failure: if a memory
 * allocation fails, data stop being appended to the buffer, but the length
 * is still updated. This situation can be tested with
 * av_bprint_is_complete().
 *
 * The size_max field determines several possible behaviours:
 *
 * size_max = -1 (= UINT_MAX) or any large value will let the buffer be
 * reallocated as necessary, with an amortized linear cost.
 *
 * size_max = 0 prevents writing anything to the buffer: only the total
 * length is computed. The write operations can then possibly be repeated in
 * a buffer with exactly the necessary size
 * (using size_init = size_max = len + 1).
 *
 * size_max = 1 is automatically replaced by the exact size available in the
 * structure itself, thus ensuring no dynamic memory allocation. The
 * internal buffer is large enough to hold a reasonable paragraph of text,
 * such as the current paragraph.
 */

FF_PAD_STRUCTURE(AVBPrint, 1024,
    char *str;         /**< string so far */
    unsigned len;      /**< length so far */
    unsigned size;     /**< allocated memory */
    unsigned size_max; /**< maximum allocated memory */
    char reserved_internal_buffer[1];
)

即獲得結構體AVBPrint的定義：

struct ff_pad_helper_AVBPrint{
    char *str;         /**< string so far */
    unsigned len;      /**< length so far */
    unsigned size;     /**< allocated memory */
    unsigned size_max; /**< maximum allocated memory */
    char reserved_internal_buffer[1];
}

typedef struct AVBPrint {

    char *str;         /**< string so far */
    unsigned len;      /**< length so far */
    unsigned size;     /**< allocated memory */
    unsigned size_max; /**< maximum allocated memory */
    char reserved_internal_buffer[1];
    char reserved_padding[size - sizeof(struct ff_pad_helper_ AVBPrint )];
} AVBPrint

 

函數format_line()

格式化日誌數據

static void format_line(void *avcl, int level, const char *fmt, va_list vl,
                        AVBPrint part[4], int *print_prefix, int type[2])
{
    AVClass* avc = avcl ? *(AVClass **) avcl : NULL;
    av_bprint_init(part+0, 0, 1);
    av_bprint_init(part+1, 0, 1);
    av_bprint_init(part+2, 0, 1);
    av_bprint_init(part+3, 0, 65536);

    if(type) type[0] = type[1] = AV_CLASS_CATEGORY_NA + 16;
    if (*print_prefix && avc) {
        if (avc->parent_log_context_offset) {
            AVClass** parent = *(AVClass ***) (((uint8_t *) avcl) +
                                   avc->parent_log_context_offset);
            if (parent && *parent) {
                av_bprintf(part+0, "[%s @ %p] ",
                         (*parent)->item_name(parent), parent);
                if(type) type[0] = get_category(parent);
            }
        }
        av_bprintf(part+1, "[%s @ %p] ",
                 avc->item_name(avcl), avcl);
        if(type) type[1] = get_category(avcl);

        if (flags & AV_LOG_PRINT_LEVEL)
            av_bprintf(part+2, "[%s] ", get_level_str(level));
    }

    av_vbprintf(part+3, fmt, vl);

    if(*part[0].str || *part[1].str || *part[2].str || *part[3].str) {
        char lastc = part[3].len && part[3].len <= part[3].size ? part[3].str[part[3].len - 1] : 0;
        *print_prefix = lastc == '\n' || lastc == '\r';
    }
}

 

函數sanitize()

對於打印信息進行處理

static void sanitize(uint8_t *line){
    while(*line){
        if(*line < 0x08 || (*line > 0x0D && *line < 0x20))
            *line='?';
        line++;
    }
}

 

函數colored_fputs()

以帶顏色的方式輸出到屏幕

static void colored_fputs(int level, int tint, const char *str)
{
    int local_use_color;
    if (!*str)
        return;

    if (use_color < 0)
        check_color_terminal();

    if (level == AV_LOG_INFO/8) local_use_color = 0;
    else                        local_use_color = use_color;

#if defined(_WIN32) && !defined(__MINGW32CE__) && HAVE_SETCONSOLETEXTATTRIBUTE
    if (local_use_color)
        SetConsoleTextAttribute(con, background | color[level]);
    fputs(str, stderr);
    if (local_use_color)
        SetConsoleTextAttribute(con, attr_orig);
#else
    if (local_use_color == 1) {
        fprintf(stderr,
                "\033[%d;3%dm%s\033[0m",
                (color[level] >> 4) & 15,
                color[level] & 15,
                str);
    } else if (tint && use_color == 256) {
        fprintf(stderr,
                "\033[48;5;%dm\033[38;5;%dm%s\033[0m",
                (color[level] >> 16) & 0xff,
                tint,
                str);
    } else if (local_use_color == 256) {
        fprintf(stderr,
                "\033[48;5;%dm\033[38;5;%dm%s\033[0m",
                (color[level] >> 16) & 0xff,
                (color[level] >> 8) & 0xff,
                str);
    } else
        fputs(str, stderr);
#endif

}

 

若是寫入文件時，調用函數log_callback_report()

static void log_callback_report(void *ptr, int level, const char *fmt, va_list vl)
{
    va_list vl2;
    char line[1024];
    static int print_prefix = 1;

    va_copy(vl2, vl);
    av_log_default_callback(ptr, level, fmt, vl);
    av_log_format_line(ptr, level, fmt, vl2, line, sizeof(line), &print_prefix);
    va_end(vl2);
    if (report_file_level >= level) {
        fputs(line, report_file);
        fflush(report_file);
    }
}

 

註釋：

1. 寫入文件時，打印數據不區分顏色

2. 輸出到屏幕時，會根據參數決定輸出的顏色