如何从avi xvid视频文件的标头中每秒获取帧? [英] How can I get the frames per sec from the header of an avi xvid video file?

问题描述

以下是avi xvid文件的前300个字节的十六进制ascii转储:

The following is a hex-ascii dump of the first 300 bytes of an avi xvid file:

|52|49|46|46|8c|79|95|00|41|56|49|20|4c|49|53|54|94|6a|00|00 RIFF.y..AVI LIST.j..
|68|64|72|6c|61|76|69|68|38|00|00|00|40|9c|00|00|00|ec|36|00 hdrlavih8...@.....6.
|00|00|00|00|10|00|00|00|81|01|00|00|00|00|00|00|01|00|00|00 ....................
|df|9e|01|00|d0|02|00|00|40|02|00|00|00|00|00|00|00|00|00|00 ........@...........
|00|00|00|00|00|00|00|00|4c|49|53|54|3c|69|00|00|73|74|72|6c ........LIST<i..strl
|73|74|72|68|38|00|00|00|76|69|64|73|78|76|69|64|00|00|00|00 strh8...vidsxvid....
|00|00|00|00|00|00|00|00|e8|03|00|00|a8|61|00|00|00|00|00|00 .............a......
|81|01|00|00|df|9e|01|00|10|27|00|00|00|00|00|00|00|00|00|00 .........'..........
|d0|02|40|02|73|74|72|66|28|00|00|00|28|00|00|00|d0|02|00|00 ..@.strf(...(.......
|40|02|00|00|01|00|18|00|58|56|49|44|00|f8|25|00|00|00|00|00 @.......XVID..%.....
|00|00|00|00|00|00|00|00|00|00|00|00|73|74|72|64|c0|28|00|00 ............strd.(..
|00|00|00|00|bc|02|00|00|90|b2|08|00|2e|5c|76|69|64|65|6f|2e .............\video.
|70|61|73|73|00|00|2e|00|70|00|61|00|73|00|73|00|00|00|00|00 pass....p.a.s.s.....
|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00 ....................
|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00|00 ....................

在这种特殊情况下，我知道视频的帧速率为每秒25帧.如何使用此转储获取帧速率?请注意，直接获取avi msvc视频文件的帧速率是很容易的，因为数据结构已被详细记录.但是，我还没有找到任何定义avi xvid文件数据结构的文档.

In this particular case I know that the video has a frame rate of 25 frames per second. How can I use this dump to obtain the frame rate? Note, it is straightforward to obtain the frame rate for an avi msvc video file since the data structure is well documented. However, I have yet to find any document that defines the data structure for an avi xvid file.

推荐答案

以下是我先前回答的改进版本(IMHO).这段代码找到了AVI文件的5个主要功能.

The following is an improved version (IMHO) of my previous answer. This code finds 5 key features of AVI files.

"""
  Purpose: To extract 5 important features from AVI files: time between frames,
           frames per second, number of frames, width and height of each frame.
   Author: V. Stokes ([e-mail])
  Version: 2014.01.01.1

  Note:
   1. DT (time between samples) in microseconds, bytes: 32,33,34,35 
      of all AVI files that I tested. Byte 0 is the first byte in the AVI file.
   2. SR (sample rate) is equivalent to fps (frames per second) and can be
      calculated from the inverse of DT. 
   3. NF (number of frames),               bytes: 48,49,50,51.
   4. WD (width of each frame) in pixels,  bytes: 64,65,66,67
   5. HT (height of each frame) in pixels, bytes: 68,69,70,71
   6. This python script works on all the AVI files that I have tested (so far),
      which suggests there is some consistency in the different AVI formats. 
"""

import os
#              laptop         desktop
dirpaths = [r'D:/Videos/', r'C:/Videos/'] 
for path in dirpaths:
    if os.path.exists(path):
        defDir = path

## All the following videos were "test AVI video downloads" from the Web
#video = 'julius.avi'                 #CRAM ( 56 frames,320x240,15fps, 66667 microseconds between frames)        
#video = 'flyby-xvid.avi'             #DIVX (495 frames,320x240,30fps, 33333 microseconds between frames) 
#video = 'flyby-xvid-realtime.avi'    #DIVX (495 frames,320x240,30fps, 33333 microseconds between frames)
#video = 'flyby-xvid-q5.avi'          #DIVX
#video = 'flyby-xvid-mpeg.avi'        #DIVX
#video = 'flyby-xvid-mpeg-q2.avi'     #DIVX
#video = 'flyby-xvid-default.avi'     #DIVX
#video = 'flyby-xvid-2p.avi'          #DIVX
#video = 'flyby-divx.avi'             #DX50
#video = 'ubAVIxvid10.avi'            #XVID (849 frames,640x480,10fps,100000 microseconds between frames)
#video = 'toy_plane_liftoff.mp4'      # This is not an AVI and doesn't work
video = 'toy_plane_liftoff.avi'      #MJPG (100 frames,640x480,25fps, 40000 microsseconds between frames)

inFile = defDir + video
print 'Input file: %s' %inFile
data = [0,0,0,0]

with open(inFile,'r') as f:
    f.seek(32,0)          # start reading offset byte 32
    data[0] = f.read(4)   # get 4 bytes (32,33,34,35) -- DT
    f.seek(48,0)
    data[1] = f.read(4)   # get 4 bytes (48,49,50,51) -- NF
    f.seek(64,0)
    data[2] = f.read(4)   # get 4 bytes (64,65,66,67) -- Width
    data[3] = f.read(4)   # get 4 bytes (68,69,70,71) -- Height
f.close()

def bufferToHex(num):
    for k in range(num):
        accumulator = ''
        buffer = data[k]
        for item in range(4):        
            accumulator += '%s' % buffer[item]
        data[k] = accumulator

# Get 4 hex strings (4 bytes in each string)
bufferToHex(4)

for k in range(4): # loop on DT,NF,WD,HT
    prev_kvs = ''
    for hexval in data[k]: # loop on each group of 4 bytes
        strr = hexval.encode('hex')   # hexidecimal string of length 2
        kvs = strr + prev_kvs
        prev_kvs = kvs

    intVal = int(kvs,16)    
    if k == 0:
        # DT
        print 'DT     = %6d (microseconds)' %intVal
        print 'SR     = %6d (frames per second)' %round(10.0**6/intVal)
    elif k == 1:
        # NF
        print 'NF     = %6d (number of frames)' %intVal        
    elif k == 2:
        # Width
        print 'Width  = %6d (width in pixels)' %intVal
    else:
        # Height
        print 'Height = %6d (height in pixels)' %intVal

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