A few things, mostly technical notes...

Wednesday, January 25, 2006

MythTV Transcoder -- what is it?

(Originally from this page. )

The transcoder re-encodes files from one MythTV format to another. The main purpose of the transcoder is to allow users with hardware encoders (PVR-250) or systems that can only record in RTjpeg due to performance reasons (multiple capture cards, slow system, etc) to create MPEG-4 streams to save space.

The transcoder can be used in two ways:

  • Automatically re-encode every file once it has completed recording
  • After marking commercials, the transcoder can be run manually to delete the commercials from the file (thus further saving space)
The two methods are independent. The first is an automatic process that can be enabled/disabled through the setup program; the second is a manual method which must be invoked on each recording individually.

The second method can be used on files that have already been transcoded (or files which were are already in the correct format), so only the frames immediately following a cut section will be re-encoded, resulting in a very minimal loss of quality.

To enable automatic transcoding, do the following: start the setup program under the host-specific settings: set the Transcoder Auto-run checkbox

For either manual or automatic transcoding: start mythbackend start mythfrontend select setup, and the Transcoding recording profile. now select either RTjpeg or MPEG-4 (selecting any of the hardware encoders will result in the transcoder not working). set the other parameters as you'd like. For best performance, you should match the audio to the 'Default' profile. If you plan to only use the manual transcoder, you can choose to set the video to be the same as the default profile too (as long as it is MPEG-4 or RTjpeg)

Everything should now be setup properly. If you elected to use the Auto-Run feature, the transcoder will automatically launch after each recording is complete. The transcoder thread runs at a low priority, so it should not impact any critical tasks or other recordings.

If you want to manually transcode a program, simply press 'X' while watching a recording (you should have already finished marking all commercials). If you change your mind, hitting 'X' again will stop the transcoding.

Once the transcode is complete, mythbackend will replace the old file with the new as soon as it is no longer in use.

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