Mythtv Transcoding recordings

Here is what I wanted to do …

Some shows that I have recorded with Mythtv I would like to keep – either move to the Videos area or burn to a DVD. In addition I would like to reduce the size of the file by cutting out commercials and cutting the start and end and also compressing using mpeg4 and with a lower quality setting.

I want to do this from the job menu on a recording.

It would also be nice to create a text file so the Video Manager can display something usefull and a thumbnail would be nice too.

First question was to determine the quality that would be good enough while keeping the size small. Others seemed happy with a 1G file for 1 hour.

My system uses a USB digital tuner ie. DVB-T and therefore recordings are mpeg2 with either mp2 or ac3 audio. Sizes are SD (720×576) or HD (1440×1080).

Doing some basic testing on a recorded file. Original recorded file = 3,874,992k – 1h 23m

Testing on the first 1min of this file with ffmpeg – note all videos have no audio.

Original mpeg2 – 1 min – 39,562k

mpeg4 @ 1000kbps 7,633k
mpeg4 @ 2000kbps 14,941k
xvid @ 1000kbps 7,772k
xvid @ 2000kbps 15,210k
xvid @ vbr q=5 16,731

The quality at 1000kbps is quite poor so it is either 2000kbps or vbr –  I think it will be vbr q=5

Estimates for sizes for a video of 60min – no audio

mpeg2 2,801,199k
xvid  1,003,860k

Also wanted to ensure that converted file would play on my DVD player so I burnt the file to a DVD and ensured that it played ok.

How to set up a Mythtv job for this

The options are

 Use built in Transcode

Cons

  • Leaves the file in the recordings directory, I want it in videos. Could create a new job running mythtranscoder and use the -o option to put it in the right place.
  • Audio processed to mp3. In theory is does not need to be. The stream in the original file could just be copied.

Pros

  • Built into Mythtv
  • Uses the cutlist

nuvexport ( and Mencoder)

nuvexport for xvid resizes and puts audio into mp3

does lossless work for streaming?
– could modify nuvexport
– What is the time impact of mythtranscode

Custom script with mencoder

Using mencoders edl option I could get the cutlist from the database and convert this to a edl file

Pros

  • mythtranscode is not needed

Cons

  • It is custom, and I have to write it
  • the edl option does not seem to work well. I have had mixed results is testing. This may be because the recording is a ts

TBC

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