nodejs实现截取上传视频中一帧作为预览图片

function fecthVideoThumbnail(entryid, index){ 
 var filename = path.join(imageDir, entryid, index + videoSuffix); 
 var thumb = path.join(imageDir, entryid, "overview",index + thumbSuffix); 
 var thumbPath = path.join(imageDir, entryid, "overview"); 
 if (!fs.existsSync(thumbPath)) { 
  <span style="white-space:pre"> </span>fs.mkdirSync(thumbPath); 
 <span style="white-space:pre"> </span>} 
 var that = this; 
 filename = filename.replaceAll("\\\\","\\\\"); 
 var cmdthumb = thumb.replaceAll("\\\\","\\\\"); 
 if(!fs.existsSync(thumb)){ 
  exec("ffmpeg -ss 00:00:10 -i "+filename+" -y -f image2 -t 0.001 "+cmdthumb+"", function() { 
    console.log(arguments[0]); 
    console.log('success'); 
    readFileEntry(thumb,that.res); 
  }); 
 }else{ 
  readFileEntry(thumb,that.res); 
 } 
  
} 

function readFileEntry(filename, response) { 
 path.exists(filename, function(exists) { 
  if (!filename || !exists) { 
   response.writeHead(404); 
   response.end(); 
   return; 
  } 
  fs.readFile(filename, "binary", function(err, file) { 
   if (err) { 
    response.writeHead(404); 
    response.end(); 
    return; 
   } 
 
   var contentType = 'none'; 
   var ext = path.extname(filename); 
   switch (ext) { 
   case ".xml": 
    contentType = 'application/xml;charset=utf-8'; 
    break; 
   case ".json": 
    contentType = 'application/json;charset=utf-8'; 
    break; 
   case ".png": 
    contentType = 'image/png'; 
    break; 
   case ".jpg": 
    contentType = 'image/jpeg'; 
    break; 
   case ".flv": 
    contentType = "video/flv"; 
    break; 
   } 
    
   response.writeHead(200, { 
    'Content-Type' : contentType, 
    'Content-Length' : file.length, 
    'Accept-Ranges' : 'bytes', 
    'Server' : 'Microsoft-IIS/7.5', 
    'X-Powered-By' : 'ASP.NET' 
   }); 
   response.write(file, "binary"); 
   response.end(); 
 
  }); 
 }); 
} 

exec("ffmpeg -ss 00:00:10 -i "+filename+" -y -f image2 -t 0.001 "+cmdthumb+"", function() { 
    console.log(arguments[0]); 
    console.log('success'); 
    readFileEntry(thumb,that.res); 
  });