[mythtv] [mythtv-commits] Ticket #799: DTV recordings sometimes show doubled recording length

Tom Dexter digitalaudiorock at gmail.com
Thu Oct 4 18:31:27 UTC 2007

On 10/2/07, Michael T. Dean <mtdean at thirdcontact.com> wrote:
> IMHO, it's a /much/ better idea to broadcast a movie recorded at 24fps
> at 1080p24 than to telecine that video just so you can transmit at "the
> usual" 1080i60.  Similarly, interlacing a 1080p30 source to transmit at
> 1080i60 is just a waste.  (Yes, both 1080p24 and 1080p30 are valid ATSC
> formats:  http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html .  When
> people say there is no "1080p" in ATSC, they mean 1080p60.)
> Now, switching resolutions may be a bit more evil for the playback
> system (depending on the smoothness with which the display transitions),
> but I don't know of any broadcasters who are doing that.
> Mike

I don't know what NBC is doing with their 1080i OTA broadcasts these
days...though I'm not very knowledgeable when it comes to technical
aspects of video.  I noticed today that when I play HD recordings from
NBC with '-v playback' it constantly disables and then re-enables
de-interlacing...apparently it sees interlaced and then progressive

2007-10-04 13:47:11.831 NVP: interlaced frame seen after 95 progressive frames
2007-10-04 13:47:11.914 Set video sync frame interval to 33366
2007-10-04 13:47:11.914 Enabled deinterlacing
2007-10-04 13:47:12.015 NVP: progressive frame seen after 4 interlaced  frames
2007-10-04 13:47:12.082 Set video sync frame interval to 33366
2007-10-04 13:47:12.082 Disabled deinterlacing
2007-10-04 13:47:12.347 NVP: interlaced frame seen after 9 progressive frames
2007-10-04 13:47:12.431 Set video sync frame interval to 33366
2007-10-04 13:47:12.431 Enabled deinterlacing
2007-10-04 13:47:12.682 NVP: progressive frame seen after 9 interlaced  frames
2007-10-04 13:47:12.749 Set video sync frame interval to 33366
2007-10-04 13:47:12.749 Disabled deinterlacing

If I manually play one of those mpeg files in mplayer, every few
seconds it reports that the frame rate has changed from 24000/1001fps
to 30000/1001fps....odd stuff.

None of this seems to happen on other 1080i broadcasts I get such as CBS or PBS.

Luckily mythtv plays them ok in spite of this.  I occasionally get
video speeding up for an instant, but only right after commercials and
even then, usually only when I'm skipping forward or back.

By the way...nobody responded to a question I had earlier about
tv_play.cpp calling NuppelVideoPlayer::SetLength() from customEvent
when it receives the DONE_RECORDING event.  In my situation (DTV
recordings only) commenting out that SetLenth() call prevents the
erroneous double length (reported by the recorder) from being used by
the OSD, and leaves it as it was from the DB and the remote encoder
and doesn't appear to cause any problems.  If nobody knows of any
potential side affects of doing this, I was thinking of posting that
to the ticket as an unsupported work around for anyone who wants to
use it.



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