如果条件为真，如何使用PHP播放视频

This file takes password input.

<html>
   <form action="playvideo.php" method="post">
   <input type="text" name="password"/>
   <input type="submit">
</html>

This file plays the video

<?php
if(isset($_POST["password"])){
   $password=$_POST["password"];
}
else{
   $password="";    
}
if($password!="pass"){  
   echo "unauthorised";
}
else{
   $local_file = 'video.mp4';
   $size = filesize($local_file);
   header("Content-Type: video/mp4");
   header("Content-Length: ".$size);
   readfile($local_file);
}
?>

Also the code works fine if I do not wrap it inside an if statement.

little changes needed....

you may try like

<?php
 if((isset($_POST["password"])) && (!empty($_POST['password']))) {
   $password=$_POST["password"]; //recommended to sanitize this input value
      if($password!="pass"){  
          echo "unauthorised";
      }else{
          $local_file = 'video.mp4';
          $size = filesize($local_file);
          header("Content-Type: video/mp4");
          header("Content-Length: ".$size);
          readfile($local_file);
      }
}else{
    echo 'password is not provided';
}
?>

password.html

<html>
<form action="playvideo.php" method="post">
<input type="text" name="password"/>
<input type="submit">
</html>

playvideo.php

<?php
  $password = ($_SERVER['REQUEST_METHOD'] === 'POST' AND isset($_POST['password'])) ? $_POST['password'] : '';
  if( $password !== 'pass')
  {
    echo 'unauthorized';
    // stop execution
    exit;
  }

  // Now only for authorized users
  $local_file = 'video.mp4';
  $size = filesize($local_file);
  header("Content-Type: video/mp4");
  header("Content-Length: ".$size);
  readfile($local_file);
  exit;

solution 2 (with session)

playvideo.php

<?php
  session_start();

  $hiddenPassword = 'pass';      
  if($_SERVER['REQUEST_METHOD'] === 'POST')
  {
      if(isset($_POST['password']) AND $_POST['password'] === $hiddenPassword)
      {
        $_SESSION['authorized'] = TRUE;
      }
  }

  if(isset($_SESSION['authorized']) AND $_SESSION['authorized'])
  {
    $local_file = 'video.mp4';
    $size = filesize($local_file);
    header("Content-Type: video/mp4");
    header("Content-Length: ".$size);
    readfile($local_file);
    exit;
  }
  else
  {
    echo 'Not authorized';
    exit;
  }

solution 3 - without session, but with hashed password and redirect.

playvideo.php

<?php  
  $hiddenPassword = 'pass';

  if($_SERVER['REQUEST_METHOD'] === 'POST')
  {
      if(isset($_POST['password']) AND $_POST['password'] === $hiddenPassword)
      {
        header('Location: playvideo.php?pass=' . hash('sha512', $hiddenPassword));
        exit;
      }
  }
  else if(isset($_GET['pass']) AND $_GET['pass'] == hash('sha512', $hiddenPassword))
  {
    $local_file = 'video.mp4';
    $size = filesize($local_file);
    header("Content-Type: video/mp4");
    header("Content-Length: ".$size);
    readfile($local_file);
    exit;
  }
  else
  {
    die('Not authorized :(');
  }

<?php
if ((isset($_POST["password"])) && (!empty($_POST['password']))) {
    $password = trim($_POST["password"]); 
    if ($password != "pass") {
        echo "Unauthorised";
    } else {
        ?>
        <video width="320" height="240" controls autoplay>  <!--Video tag introduced in HTML5-->
            <source src="video.mp4" type="video/mp4">
            Sorry, your browser doesn't support the video element.
        </video>
        <?php
    }
} else {
    echo 'Password is not provided';
}
?>