Too Busy For Words - the PaulWay Blog

Wed 14th Mar, 2007

MythTV Transcoding HOWTO

My brother has recently installed MythTV. Well, he installed MythTV, and then called me to get the TV guide and channel settings sorted out. But his was the dirtier job: crawling up into the roof to splice in a new (powered) aerial splitter. His signal to noise ratio and signal strength aren't great, but it works.

Now to help him learn how to use the thing :-)

Murray Wayper wrote:
> How do I transcode existing files?

The first thing to do is to edit the commercials and stuff you don't want out.

You do this by going into the show and pressing 'e' to edit the cut list. This is presented as a bar across the bottom. If the show has been commercial flagged - and, by default, any show on a commercial station will have been - you can press 'z' to import the commercial cut list that the commercial flagging process has determined. That will give you a list of regions. (Incidentally, commercial flagging also puts in a superfluous cut point at the start and end, so I remove them otherwise I get a half a second of the start and end of the recording tacked onto my transcoded programme.)

You navigate with the arrow and pageup/pagedown keys. Left and right move by the interval specified at the bottom right; up and down change that interval. You start at one second, and can go down to one frame and up to ten minutes. Pretty quickly you develop the technique of homing in on an ad break by a sort of binary subdivision method - start at a minute and move forward until you're in the ad break; then go down to twenty seconds and move out of the ad break; then go down to five seconds and move into the ad break, and so on. Press Space to insert a new break point - it'll ask you which direction you want it to go. The default direction alternates, so you usually don't have to change your selection. If you're close to an existing break point you can move it (useful for fixing the commercial detection, which isn't flawless), delete it, flip it around, or leave it alone.

Page up and page down move between the break points. This is very useful for checking that the commercial detection has worked - set the jump interval to a second, then move to the first point and check either side. Move the break point if necessary, then use page down to move to the next break point and so on. Here's where you remove the superfluous break points that commercial detection puts in at the start and end of the show. It takes a little while to get the hang of this kind of editing, but you get used to it. You press 'e' when you're finished with the cutlist editing mode.

To start transcoding, you can do two things. If you're watching the show, you can press 'x' on the keyboard and it will start transcoding using the default profile for that show. So once I've finished editing the cut list, I usually skip about two seconds back into the end of the show, press 'e', and immediately press 'x' just before the show ends at the new cut point. Alternatively, from the 'watch recordings' menu, when you're looking at the particular show you want to transcode, press the right arrow and choose 'job options'. Then 'transcode', and choose the profile you want to use. High quality basically leaves the MPEG2 stream as is and just removes the commercials from it; Medium quality and Low quality involve a transcode down to MPEG4 (Xvid). You can set up the actual parameters of how much compression and so forth in the setup menu.

BTW, you'll also find it useful to know that you can press 'd' when watching a show to jump back to the 'watch recordings' screen and go into the 'delete show' menu. (I.e. you do get to confirm whether you want to delete the show or not, but it's faster than exiting the show, pressing right, and choosing delete.) And, for shows that have commercial detection that haven't been transcoded, you'll see a little box in the top right corner (I think) informing you of an upcoming commercial. At this point you can press 'end' to skip to the end of the commercial flagged region.

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