[mythtv-users] Playback problems with 'local' DVB-T transports in the UK

[John Pilkington]

I have recordings from two main-chain Freeview masts in the UK - 
Waltham, East Midlands and Sandy Heath, serving Cambridgeshire.  I 
believe Waltham uses 6 DVB-T transports, and Sandy Heath 4.  In each 
case most are QAM-64, with which MythTV works well, and one is QPSK, 
which, for me, is giving minor problems;  these may perhaps have 
something in common with those seen recently with some MPEG2 channels in 
the USA.

I have compared mediacodec results from one of the 'Local' channels with 
BBC2,  but email formatting would confuse a diff -yd printout.  It looks 
as if the main changes are:

Format settings, GOP               : M=5, N=50   vs Variable
Format settings, picture structure : Field       vs Frame
Active Format Description          : None given  vs Letterbox 16:9 image

Time code source                   : Group of pictures  vs None given
GOP, Open/Closed                   : Closed             vs None given	

mediacodec reports that both are interlaced, top field first, but 
mythffmpeg -i says the local channel has bottom field first.


2012-model Panasonic TVs report bad signal quality and give blocky 
pictures from Waltham local (for which ISTR that the M,N values differ 
from those above) but seem happy with a stronger signal from Sandy Heath.

The Project-X demuxer, which I use in mythDVBcut, is known to fail on 
rare occasions when timestamps go backwards.  With the 'Local' channels 
it fails completely.

> dropping GOP# 168 @ orig.PTS 08:36:06.846 (2787016224), errorcode: 24
!> Pics exp/cnt 25/50, inGOP PTS diff. 20ms, new Timecode 00:00:00.000
!> dropping GOP# 169 @ orig.PTS 08:36:07.846 (2787106224), errorcode: 24
!> Pics exp/cnt 25/50, inGOP PTS diff. 20ms, new Timecode 00:00:00.000

... and the editor's '5-second' step gives exactly 4s.

I tried mythtranscode --mpeg2 but got nothing usable.

VDPAU seems to give blocky pictures initially but then settles. 
mythffmpeg decoding with old intel graphics has just worked.

John P
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Correction: for mediacodec above read mediainfo