[mythtv-users] HDMI capture card with linux drivers

Douglas Peale Douglas_Peale at comcast.net
Fri Apr 16 06:15:48 UTC 2010


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Raymond Wagner wrote:
> On 4/16/2010 01:24, Douglas Peale wrote:
>> Your computer could do nothing else but write the disk, so there is no
>> possibility of encoding while recording.
>>    
> 
> Why not?  Obviously the BlackMagic Windows software already performs
> this impossible task of encoding to MJPEG on the fly.
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Unless they are using a raid system, they are not writing the
uncompressed file directly to disk.

See current performance figures for 2 TB hard drives:
http://www.storagereview.com/western_digital_caviar_black_review_2tb

So, they must be doing real time compression.

Are you sure they are doing this in software? I'm not aware of any
software that can handle HD compression in real time on a PC. Unless of
course you don't care about the quality.

Non real time compression is doomed because it must buffer to disk since
there is no way you are going to get 1.3 TB of ram in a system. And in
order to use a disk buffer, you must simultaneously write the
uncompressed data to disk (already an impossibility with current
drives), read that uncompressed data, compress it, and write it back out
to the drive.

I missed the beginning of this discussion. I understand you want to
record HDMI signals. I'm assuming you want to do this because that is
what you get out of your cable box. You do realize that this data is
encrypted don't you? How do you plan on decrypting it? The only time it
might not be encrypted would be if it was broadcast in clear QAM in the
first place. In that case you would be much better off just saving the
already compressed data before it gets uncompressed and sent over the
HDMI cable.
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