计算flv视频文件长度？使用纯PHP

<?php
function getFLVVideoDuration($file_path) {
    $file = fopen($file_path, "rb");
    if (!$file) {
        return false;
    }

    // 读取FLV文件头部
    $header = fread($file, 9);
    if (!$header || substr($header, 0, 3) !== "FLV") {
        fclose($file);
        return false;
    }

    // 读取第一个tag的数据
    fseek($file, 9);
    $tag_header = fread($file, 11);
    if (!$tag_header) {
        fclose($file);
        return false;
    }

    // 解析tag的类型和数据大小
    $tag_type = ord($tag_header[0]);
    $data_size = unpack("N", substr($tag_header, 1, 3))[1];

    // 读取tag的时间戳
    fseek($file, 4, SEEK_CUR);
    $timestamp = unpack("N", fread($file, 4))[1];

    // 计算视频时长
    $duration = 0;
    while (!feof($file)) {
        if ($tag_type === 9 || $tag_type === 8) {
            $duration += $timestamp;
        }

        fseek($file, $data_size + 4, SEEK_CUR);
        $tag_header = fread($file, 11);
        if (!$tag_header) {
            break;
        }

        $tag_type = ord($tag_header[0]);
        $data_size = unpack("N", substr($tag_header, 1, 3))[1];
        $timestamp = unpack("N", fread($file, 4))[1];
    }

    fclose($file);

    return $duration / 1000; // 转换为秒
}

// 使用示例
$file_path = "path/to/your/flv/video.flv";
$duration = getFLVVideoDuration($file_path);
if ($duration !== false) {
    echo "FLV视频文件的长度为：" . $duration . "秒";
} else {
    echo "无法获取FLV视频文件的长度";
}
?>