[mythtv] ... channel change times....?

Erez D erez0001 at gmail.com
Thu Jul 12 07:30:23 UTC 2007

for a long time, i used myth, and wondered why vdr channel change is faster.

i created an app that can control diseq, change channels, etc and write to

then did somthing like:
myapp > file & tail -f file | mplayer -

to my astonishment, i was able to switch channels a lot faster than myth
(usually less then a second)
(i had to do somthing similiar to NAT for pids so when i change channels,
the video and audio stream keeps their pid)
but the problem was that mplayer sigsegv somtimes when switching channels as
the video and audio streams changed format when i changed channels.

i tried to rerun mplayer for each channel. i had worse swithing times as
mplayer tried to detect the pids.
but when i told it what pids it was, channel change was very fast. even
though i started a new file and restarted mplayer for each channel change.

so i really do not see the reason it takes so much time to change channels
in myth
if the frontend will know in advance what the pids are (this info can be
cached as channles do not change pids so often)
and will not need to scan the stream for it.
note also that when changing channels, as we usually watch in no delay
related to real time, if frontend and backend are on the same machine, then
the data written to file still sits in the kernel's cache and it should not
need time to get it from disk

so as far as i see it. channel changing speeds, could be a lot faster in
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