[mpeg2] Re: More questions about the MPEX driver

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Wednesday 12 May 2004 09:07, you wrote:
> Hi all,
>
> after some explanation from Gerd Knorr, and after reading the driver's
> code, I understood the buffering problem that I was having, and I am
> doing some experiments for tuning the TS_NR_PACKETS value (hey, with
> TS_NR_PACKETS = 1 I get no jitter on the PCR!!! But the stream is
> corrupted...)

argh.

> In the meanwhile, I have some other questions about the MPEX board, and
> the driver:
> 1) I see that the generated TS has video PID = 256, audio PID = 259, and
> PCR PID = 260. Is it possible to change such values? Looking at the
> driver, they seem to be hardcoded in it, but I hope that the hardware
> permit to configure the PIDs... How difficult would it be to fix the
> driver?

yeah, its possible - you'd have to write the values you want to the TS PID 
registers, and recalculate the (currently hardcoded) PAT/PMT tables. The 
driver doesn't do this right now.

BTW: I think the driver would have to stop+start the encoding process to 
change the PIDs - I doubt its doable on the fly.

> 2) Would it be possible to generate a TS with PCR PID = video PID?

I think so - you can specify which PID should contain the PCR independently of 
specifying the video/audio PIDs... but again the driver doesn't yet expose 
this interface to userspace.

> 3) How can I set the stream parameters (bit rate, CBR vs VBR, ...)? I
> think I must use some ioctl() on /dev/video0... Where is is documented?

There aren't any standard APIs for setting that sort of thing in linux, so I 
had to make it up myself. Have a look at MPEG_SETPARAMS in saa6752hs.h 
though. I tried to expose as many of the bitrate parameters as I could.

> 4) It seems that the audio volume is a bit low (I have an MPEX board
> without tuner, BTW). I already tried things like "v4lctl volume 100", or
> similar, but it is still low... Is anyone seeing similar problems? Any
> suggestion?

I always just adjusted the analogue input volume - not sure if its 
configurable in the hardware (and it won't be in the saa6752hs bit if it is).