[mythtv-users] Requirements

Niels Dybdahl Niels at Dybdahl.dk
Mon Mar 20 08:07:04 UTC 2006

On 3/20/06, Jonas Lihnell <roze at roze.mine.nu> wrote:
> I assume my last mail was too broad and covered an issue too big so
> I'll split it down to a few more specific questions. (old mail:
> http://mythtv.org/pipermail/mythtv-users/2006-March/129099.html)
> When the backend sends the tv signal to the frontend, do the backend or
> the frontend decode it? (I assume frontend)

The frontend does the decoding. Note that with XV the CPU in the
frontend does the decompression, while the GPU does the scaling. With
XvMC the GPU does more of the job. With MPEG2 on a PVR-350 TV-Out, the
GPU does all the decompression.

> When myth takes an incoming signal, does it reencode it before it write
> the buffer to disk, or do it first write the raw stream to disk, then
> reencode it to my livetv profile? (I hope it reencodes it before
> writing to disk)

I am not sure what your "livetv profile" is, but with a PVR-x50 tuner
board, the tuner board does the MPEG2 compression and the result is
stored as it is on the disk. With a DVB tuner board, the signal is
already MPEG2 compressed and is stored as such on the disk.
The signal from cheap tuner boards without onboard compression is
compressed on-the-fly by the mythbackend to MPEG4 or RTJPEG and then
stored on the disk.
Afterwards the shows can automatically be transcoded from MPEG2 or
RTJPEG to MPEG4, if you choose to.

Niels Dybdahl

More information about the mythtv-users mailing list