[Matroska-devel] Downloading only audio portion from a matroska file

[Shashank Tulsyan]

Hi,

I am making a downloader, called Neembuu http://neembuu.sourceforge.net .
I install a extension to the native file system, and makes virtual files 
and folders represeting files being downloaded.
When these files (take a media file for examle) are opened in a program, 
like vlc; VLC requests some portion of the file,
this is downloaded. If the video is forwarded the request point shifts. 
The filesystem and downloader being multithreaded.
The source an be http links or bittorrent, or both together.

I tested this on Http yesterday, and it worked for the first time.

I had also done tests (but with files on hard disk rather than on the 
internet) attempting to
request only audio part from a video file. I used mkvtoolnix.
For avi files, mkvtoolnix (sorry but i don't know which demuxers it uses 
for avi)
can requests only audio portions, skipping video part.
And I obtain the following request pattern :
Audio extracted from a 200MB anime using mkvtoolnix

The request pattern is really small if it is stored as VInt , something 
like 100KB, and after compressing really small 9KB because there is a 
simple pattern (the size of every atomic request is mostly same ).

This type of testing is not possible with mkv using mkvmerge atleast, 
and it seems to be the tool available for matroska files.
I would like to do the same testing with a mkv file, uploaded somewhere, 
and see
if it is practical to extract only audio.
That is

Total actual download (downloaded data + payload) while downloading only 
audio < or > Total actual download when downloading the whole file
And also compare the time to see if it would be senseful to do so.

But mmg requests the entire file.
The point of using this download feature is to download less. So i was 
wondering how can it be possible in mkv to extract only one track and 
while doing so, not make unncessary request.
By unncessary i mean tracks other than audio.
I am not well versed with EMBL and mkv, but I am assuming that it is 
possible to find exact location of audio tracks, and in mkv file audio 
and video occur AudioVideoVVVAVVVVV.... .
Or am I wrong, and exact location is unpredictable, and cannot be found 
without reading/requests the video part as well.

MKV is really advanced, so i think it should be possible to find audio 
portions.
Well is it?
If yes how can I do this?
If  no, i think I can make a map of audio portion and attach to the mkv 
file and later use this. Would this work (although i'd rather hope that 
I don't need to do it this way)
Please reply .


Regards
Shashank Tulsyan


BTW, If you are interested, this a previes of the test/experimental 
downloader that worked yesterday :
http://neembuu.sourceforge.net/wiki/index.php/File:FIRST_SUCCUSSFUL_WATCH_AS_YOU_DOWNLOAD_THE_NEEMBUU_STYLE.png
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