[mythtv] Bugfix: ATSC shouldn't = 25 fps

Keith Irwin kirwin at ncsu.edu
Mon Jun 6 07:21:10 UTC 2005

Presently, if someone has a mix of ATSC and NTSC cards installed, in 
the if/else statement which begins on line 69 in 
libs/libmythtv/recorderbase.cpp, there is no ATSC case, so it falls 
through to the PAL case.  Clearly this has not been updated since 
whenever ATSC was added as an option on the TV Format drop-down in 

As a result, if you tell it that your TV Format is ATSC, you get 25 fps 
for any analog capture cards which you have attached.  This would only 
be desirable, if a user had both ATSC and PAL or SECAM capture cards, 
which seems highly unlikely.  Because an ATSC capture card does not do 
frame-rate adjustments since the frame rate is determined by the 
incoming MPEG stream, these settings do not affect ATSC capture.  But 
if a user had a mix of ATSC and NTSC cards (as I do), this results in 
the NTSC cards capturing at 25 fps.  The obvious work-around is to 
switch to NTSC as your listed TV Format, but there are several HOWTO's 
(including the one from the EFF) which specifically tell people using 
ATSC cards to switch it to ATSC, so really we should fix it so that 
29.97fps is the default when ATSC is selected, especially for people 
who might use the NTSC mode on their HD2/3000 sometimes.

As such, I have included a .diff below which is a bug fix for this 
issue.  It adds one more case to the first if clause to add ATSC in 
addition to NTSC and NTSC-J.  It also adds comments to that section 
both about the change and what the code is doing in general.  Hopefully 
they aren't too verbose for the liking of the code maintainer, but I 
wanted to make sure that all the bases were covered since the issue may 
need to be revisited at some point in the future if someone makes a 
card which can capture HD via component inputs or some other similar 
method where MPEG-2 streams are not automatically produced.

Keith Irwin
-------------- next part --------------
A non-text attachment was scrubbed...
Name: atscframeratefix.diff
Type: application/octet-stream
Size: 951 bytes
Desc: not available
Url : http://mythtv.org/pipermail/mythtv-dev/attachments/20050606/ea447fb8/atscframeratefix.obj

More information about the mythtv-dev mailing list