class Reader():
  def __init__(self, content): # content (bytes):FLV文件的二进制内容
    self.content = content
    self.start = 0
    self.eof = False # 判断是否已读完全部内容
    self.length = len(self.content)
    
  def read(self, n=1):
    # 设置 if 语句防止过度读取内容
    if self.length > (self.start + n):
      out = self.content[self.start:self.start + n]
      self.start += n
    else:
      out = self.content[self.start:]
      self.eof = True
    return out

def add_flv(flv, target, videoTimeStamp, audioTimeStamp): # 修改并添加 Tag 的函数
  with open(flv, 'rb') as f:
    content = f.read()
  reader = Reader(content)
  header = reader.read(13)
  with open(target, 'ab') as f:
    while not reader.eof: # 一直读取直到读完，此时 reader.eof = True
      dataType = reader.read(1)
      dataSize = reader.read(3)
      timeStamp = int.from_bytes(reader.read(3), 'big') # 将 3 字节转换成整数
      headerRemained = reader.read(4)
      if dataType == b'\t': # 视频
        timeStamp += videoTimeStamp
        videoTS = timeStamp
      if dataType == b'\x08': # 音频
        timeStamp += audioTimeStamp
        audioTS = timeStamp
      timeStamp = timeStamp.to_bytes(3, 'big') # 将整数转换成 3 字节
      tagHeader = dataType + dataSize + timeStamp + headerRemained
      tagData_andSize = reader.read(int.from_bytes(dataSize, 'big') + 4)
      f.write(tagHeader)
      f.write(tagData_andSize)
  return videoTS, audioTS
def merge_flv(flvs, target): # 主函数
  videoTS = 0
  audioTS = 0
  for i, flv in enumerate(flvs):
    with open(flv, 'rb') as f:
      content = f.read()
    reader = Reader(content)
    
    header = reader.read(13) # flvHeader + tagSize0
    if i == 0: # 写入第 1 个FLV视频的文件头
      with open(target, 'wb') as f:
        f.write(header)
        
    videoTS, audioTS = add_flv(flv, target, videoTS, audioTS)

import time
since = time.time()
flvs = ['m1.flv', 'm2.flv', 'm3.flv', 'm4.flv'] # 视频大小：45MB，20MB，59MB，54MB
target = 't.flv'
merge_flv(flvs, target)
end = time.time()
print('Merging flvs takes {:.2f} s'.format(end - since))
# Merging flvs takes 0.88 s