[linux-dvb] Re: struct dmx_input_t

[Johannes Stezenbach <js@convergence.de>]

Aurelian Pop <puiu@cs.tut.fi> wrote:
>
> I mean what is the difference if in apps/test/test_dvr.c I change from
> DMX_IN_FRONTEND to DMX_IN_DVR??? As far as I know, everything behaves the same.
> Am I totally in the woods?? :)

When recording, the stream can only come from the frontend, so the
current implementation ignores the input parameter.

> > The actual implementation is not very intuitive, however. A filter
> > opened with DMX_IN_FRONTEND *after* the dvr device has been opened
> > for writing will get the stream from dvr. Why? Just one more bit
> > of broken dvr device semantics...
> 
> Please explain what did you mean with "... get the stream from dvr".

The av7110 implementation has actually two demuxes: one in hardware,
and one in software. When you write to the dvr device, the data goes
to the software demux, *and* any filters you set (regardless of the
input paramter) will be set in the software demux. The reason this
was implemented that way is: DMX_SET_SOURCE was only invented recently
and is not properly implemented, so it was assumed to "be the right
thing". That way you can e.g. replay a TS with test_dvr_play and
analyze the stream withn scan, without having to change the filter
settings in scan.c.

In the current implementation it's best to use the dvr device for
TS recording and simple playback only, and keep the fingers off it
otherwise.
The "V4" version of the DVB API will attempt to clean this up.


Johannes


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