[linux-dvb] Re: FF cards alter PTS'?

[Johannes Stezenbach <js@convergence.de>]

Pekka Virtanen wrote:
> 
> I have two computers, one with Full featured DVB-C the other with a 
> Budget DVB-C. I ran the same software on both computers, on the same 
> channel and the same time of course.
> 
> The software prints the video PTS on the console. The results are below:
> 
> FF DVB-C:
> video pts = 5581899604
> video pts = 5581942804
> video pts = 5581986004
> video pts = 5588682004
> [...]
> 
> BUDGET DVB-C
> video pts = 7682452818
> video pts = 7682496018
> video pts = 7682539218
> video pts = 7682582418
> [...]

Can you print that in hex to see if there is just one bit flipped?

Could you make the software available that produces this output?

> The BUDGET results correspond to the subtitles PTS (I'm trying to sync 
> subtitles).
> 
> On FF DVB-C video pts << subtitle pts, so the synchronization does not 
> work. I'm using STC for syncing but it's about the same as the video pts.

The STC is fed from the adaptation field of the TS packet header (PCR
PID), the video PTS are from the PES packet header. It's good that
PTS == STC.

> What's going on here? Why are the pts / stc altered on a full featured 
> card? Does the card itself modify the pts values or the driver? Can I 
> somehow modify the subtitle pts' to match the stc?

The av7110 destroys the adaptation fields if you record and watch
at the same time (record with DMX_PES_OTHER to prevent this). However,
the DMX_GET_STC should give you correct values. Also, AFAIK the PES
header is not altered by the av7110 or firmware, so the PTS should
be correct. Or maybe the 33rd bit of the STC/PTS gets lost?


Johannes


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