Please describe the problem:
for inspecting media files I use gst-python's gst.extend.discoverer, which works pretty well on most media files, but with mpeg1/2 files I get different durations nearly every time. The time diff affects video as well as audio length and the diff is up to 3s with a small 30s file.

happens on my current Debian/sid installation with
gstreamer-0.10.19
gst-plugins-ugly 0.10.8
gst-python 0.10.11
mpeg2dec 0.4.1
as well as some older installations I was able to test

Steps to reproduce:
# discoverer stress test

import sys
import gobject
gobject.threads_init()

import gst
from gst.extend.discoverer import Discoverer

i = 0
min_vlength = gobject.G_MAXLONG
min_alength = gobject.G_MAXLONG
max_vlength = 0L
max_alength = 0L

def finished(d, result):
    global i
    global min_vlength, max_vlength
    global min_alength, max_alength
    min_alength = min(min_alength, d.audiolength)
    max_alength = max(max_alength, d.audiolength)
    min_vlength = min(min_vlength, d.videolength)
    max_vlength = max(max_vlength, d.videolength)
    print 'A: %d V: %d' % (d.audiolength, d.videolength)
    i += 1
    if i >= 100:
        print 'MIN A: %s MIN V: %s' % (gst.TIME_ARGS(min_alength),
                gst.TIME_ARGS(min_vlength))
        print 'MAX A: %s MAX V: %s' % (gst.TIME_ARGS(max_alength),
                gst.TIME_ARGS(max_vlength))
        loop.quit()
    else:
        del d
        d = Discoverer(filename)
        d.connect('discovered', finished)
        d.discover()

filename = sys.argv[1]
d = Discoverer(filename)
d.connect('discovered', finished)
d.discover()
loop = gobject.MainLoop()
loop.run()


Actual results:


Expected results:


Does this happen every time?


Other information: