[ivtv-devel] MPEG PTSs drifting away

Boris Dores babal at via.ecp.fr
Fri Jul 18 17:00:13 CEST 2008


  Hello everyone,

  Yesterday I just got an Hauppauge WinTV-PVR-USB2 device (model 29039),
in addition to the WinTV PVR-250 (model 48016) I've had for a few years
now.

  I wrote my own demuxer a while ago to check the integrity of recorded
streams before I replex them with mjpegtools and burn them with
dvdauthor.

  Using this demuxer, I saw that video PTSs (and audio ones too but
that's a bit less obvious to detect in the current implementation)
are slowly drifting away in the streams that are recorded with the
WinTV-PVR-USB2: there is a gap of 300 units (often positive but
sometimes negative) approximately every 3rd GOP.

  Of course I COULD modify my demuxer to just deal with it, provided
that the drift is slow enough to be sure there is no gap in the input
stream: this is even probably a feature I SHOULD implement sooner
or later (and I cannot even guaranty that I didn't miss any MPEG
subtility).

  However, the thing is that the ivtv driver used to display the same
behaviour (I still have a few streams from that time), but hasn't
anymore since at least version 0.4.4.

  Both the WinTV-USB2 and the WinTV PVR-250 are installed in the same
linux box, which means same Debian stock kernel 2.6.18, same support
chips, same kernel chip-level drivers. The only difference between them
(except hardware of course !), is the pvrusb2 driver (the one included
in 2.6.18) on one hand, and the ivtv driver (version 0.10.6) on the
other.

  So I wonder if there isn't something that could be done in the driver.

  Thank you very much for any insights and ideas you might have.

-- 
Boris Dorès



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