[mythtv-users] Compressing Streamed Data. . .?

Michael T. Dean mtdean at thirdcontact.com
Sat Jun 2 15:48:06 UTC 2007


On 06/02/2007 11:10 AM, Michael Williams wrote:
> I've currently got a MythTV backend running downstairs.  I've got two  
> computers upstairs that I watch it on.  One problem I'm having,  
> however, is the amount of data that is being streamed across the  
> network.  When there is only one viewing machine I has the ability to  
> bring my router to it's knees, resulting in everyone on the network  
> being disconnected.  I've tried connecting over SSH with compression,

Note that the entire purpose of video encoding is to compress video
data.  And, while "general-purpose" compression algorithms like bzip2 or
gzip or zip give "good" compression, application-specific compression
algorithms (like MPEG-2 or MPEG-4) give "very good" compression. 
Therefore, further compression will do little, if any good, and often
has the opposite effect (actually making the data take up slightly more
room).

To verify, try running:

bzip2 --keep /path/to/recording.mpg

And then look at the filesizes.

> but all that does is result in choppy video.

At that point, you're asking your CPU to compress already compressed
data (which is significantly more work than compressing uncompressed
data) and encrypt data before transmission and the frontend has to
decrypt and uncompress the data before decoding it (which is also a
further decompression).  Therefore, you're probably maxing out the CPU
(and gaining nothing from it).

> Are there any myth  
> settings for strictly streaming?
>   

Are you using NFS?  If so, you likely need to adjust your NFS options. 
There are several good posts that discuss recommended options here on
the list as well as pages in the wiki.  If not, you may need to look
into your network configuration, but there are some settings you can use
to affect the streaming.  Generally, though, they're not going to be the
reason that you can't do 2 transfers concurrently (that typically
indicates a larger problem).

Mike


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