[mythtv] [DVB] Confused about TS/PS and HW/SW mode? Read this...

Jesper Sörensen jesper at datapartner.se
Tue Apr 19 14:29:54 UTC 2005


A quick recap for those of you who haven't followed the lists for the 
last months:

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
TS/PS:
TS, ("http://www.linuxtv.org/wiki/index.php/MPEG2_Transport_Stream"), is 
the original/raw format used in the DVB data stream. When Myth records 
in TS mode it filters out unwanted pids (other channels & unwanted 
streams) and does some minor rewriting of the PAT/PMT etc, but basically 
it saves the data in its original format.

In PS mode, Myth converts the incoming TS data into PS 
("http://www.linuxtv.org/wiki/index.php/MPEG2_Program_Stream") format 
before writing it to disk. PS format has slightly less overhead than TS 
so it takes a few percent less space on disk, but it doesn't cope with 
errors as well as TS, and since the TS->PS transform in Myth is pretty 
"quick & dirty" it's likely to contain bugs and it won't handle the 
"advanced" features planned for Myth (teletext, subtitles, MPEG-4 
audio/video etc...)

Unfortunately TS recording still has bugs though (or rather the 
*playback* of TS), e.g. the loss of audio in live TV when changing 
between two channels that use the same audio pids. DTK and Taylor are 
working on a fix but it's not finished yet.

Once TS recording works 100%, PS is planned to go away.

So, TS is preferred if it works for you (or you can live with the Live 
TV audio bug).

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
HW mode:
The "HW mode" switch makes Myth treat the DVB card as if it was a FF 
card ("http://www.linuxtv.org/wiki/index.php/Full-featured"). It doesn't 
actually have to be a FF card, it's just about which settings to use 
when setting up the demux and stuff.

Normally we always want to use the card in sw (budget) mode, because hw 
mode cannot handle more than one audio stream (or video for that matter 
but myth doesn't either at the moment), and the hw decoder can't be used 
by Myth anyway.

There are also some budget card drivers that don't work in hw mode, but 
most seem to silently accept it which means you get sw mode anyway, but 
with the limitations of hw mode. On the other hand, some drivers (e.g. 
the DEC2000-t) doesn't work in sw mode so it has to use hw mode.

Basically, sw mode is preferred but if that doesn't work, try hw mode. 
Might also be a good idea to create a bug report for the DVB driver, 
because you probably don't want to use hw mode forever because of its 
limitations.

IIRC, Myth < 0.16 always used HW mode, 0.17 always used SW mode and 
since 0.18 there is a switch.

There are also some people having problems with multiple audio streams. 
As far as I know, this is caused by a XvMC bug, being unable to handle 
multiple streams properly. Try helping the XvMC devs to fix it, disable 
XvMC, or try enabling hw mode as a workaround (which will limit 
recordings to one stream). If you have this bug and are NOT using XvMC, 
please let me know.



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