Quote:
Originally Posted by Stream Recorder
Ok, I'm not asking how you can prove that there is any corruption. But can you show any recorded stream where corruption can be noticed?
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Last year i had sets of test url's which would have served our discussion; the company turned the lights off for all those mms and rtsp url's (or deleted the files) so i dont have anything good (a file, a url) at hand, sorry. Just from my extensive testing back then I made some general observations regarding (streamed) *.WMA-files (*.ASF), contradictory in a way:
1. if you have 1 test-url and use 10 different tools on it, you get 3-4 different files (crc32, file sizes). all 4 files play just fine in software players (VLC, WMP, foobar2000, Winamp, ..), i.e.
the WM-format seems resistent/robust against "corruption". Corruption in the sense, the files are not 100% identical with the server file. Maybe 1 is, but the other 3 arent (crc32, file size). Having 4 different files, it is a challenge to know/decide/determine which one comes closest to the 100% of the original server file. How would you know that WMR's download result is the perfect one? (but this not unimportant question is not the topic of this post nor of this thread)
2. i had, too, WMA-files which had identical file sizes on the hdd, downloaded from different builds of the tools. A
binary visual comparison revealed that the files were essentially the same except for 1-2 Bytes in the body (middle of the file). The one downloaded file played fine in WMP and foobar2000, the other one produced a clear error message ("file is corrupted.. blablah") both in WMP and in foobar2000, i.e.
the WM-format seems sensitive to any slight corruption.
3. i've just tried to corrupt a WMA-file by
changing 3 consecutive Bytes in the body of the file. Clearly, the file is
corrupt in the sense that it is not original (crc32) anymore. And? The file plays fine, without error messages, both in WMP and foobar2000. This observation is in contrast to
2. and it answers your question as "no, corruption cannot be noticed".
Here we have our contradiction. My report (without any documenting proof or anything). And to answer your question: No, i cant show any such file (or url) because i deleted all corrupt files (and test file downloads from back then), but yes, corruption can be noticed during playback.
2. states that very slight changes of Bytes in the middle of a WMA-file suffices to corrupt the entire file. A shocking observation. (and
3. shows that it is not very easy to demonstrate this degree of sensitivity by manual manipulation).
As you pointed out, users dont need to care (because they will never know) if their recorded WMA (WMV, ASF, etc.) material is not original or exact. If the material plays without error messages, then no reason to complain. i never complained either. I am grateful for any tool which saves playable WMA/ASF files!
In summary, corruption can be noticeable (see 2.) but in most cases isnt (see 1. and 3.).
11-14-2010, 03:29 AM
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