[mythtv-users] Commercial Flagging vs. Transcoding

[Joseph A. Caputo]

On Wednesday 18 February 2004 16:36, John DeLuca wrote:
> I currently transcode all recordings (set to kick off immediately
> following completion of recording).  I don't intend to save the
> files...I merely transcode to have the commercials flagged so when I
> watch them later, I can skip past them (assuming it's done a good job
> of properly detecting commercials).
>
> In reading another post, I am wondering if I really need transcoding?
>  I have a PVR-x50 and the recording profiles are set up for MPEG2- at
> 2200 bits for 720x480.  That's also the setting of transcoding.  My
> questions are:

Ummm... are you sure about those recording parameters?  MPEG-2 720x480 @ 
a bitrate of 2200.... should be pretty much unwatchable.  However, 2200 
is a pretty decent bitrate for MPEG-4, if that's what you're 
transcoding to.  I'd guess your MPEG-2 bitrate is much higher (like 
about 3x higher).


> 1. Do I benefit from transcoding other than for commercial detection?
>  I assume there's perhaps some space saving since Iguess I go from
> MPEG2 to MPEG4 in the transcoding process.

You don't need to transcode to detect commercials.  If you have the 
"Automatically Flag Commercials" option on, then all shows will have 
their commercials flagged when the recording is finished.  You do save 
some space by transcoding from MPEG-2 -> MPEG-4, but if you're not 
keeping the recordings, you might want to think about whether it's even 
worth it.

Transcoding has absolutely nothing to do with automatic commercial 
detection.  The transcoded file still has the commercials (though you 
can skip them if they've been flagged).  If you want to actually cut 
the commercials out of the file (good for saving even more disk space 
or for archiving), then you need to edit the cutlist.  Start watching 
the recording, press 'M' to enter edit mode, then 'Z' to load the 
commercial cutlist.  Now the cutlist is loaded with the auto-detected 
commercials (if the commflagging has finished).  You may now tweak the 
cutpoints & exit edit mode.  *Now* if you transcode, the commercials 
(and any other edits) will actually be left out of the transcoded file.


> 2. If there's little/no benefit to transcoding (if I don't plan on
> saving the recordings after I watch them), should I just use the 
> mythcommflag before going to bed or on a schedule if that's the only
> real goal?

Just turn on "Automatically Detect Commercials" in the frontend setup.  
Commercial detection will run after each recording is finished.  It 
shouldn't really disrupt anything, as it's nice'd.  On my Athlon XP 
1600+, I can simultaneously record a program (software encoding) and 
watch a program, while a previous recording is having its commercials 
flagged.

-JAC