[mythtv-users] HD MPEG-2 to MPEG-4 transcoding

[Brad Templeton]

On Sun, Jul 16, 2006 at 11:18:59PM -0700, Yeechang Lee wrote:
> My 3.0GHz Pentium 4 frontend/backend took 458 minutes to transcode,
> without resizing and at a 5000Mbps bitrate, a 15.7GB 125-minute HDNet
> (18000Mbps) Movies recording to a 5.7GB MPEG-4, a 3.67:1 time ratio
> and a 64% space savings. (Both mythbackend and mytfrontend were active
> at various times during the process.) I'd love to see mythtranscode be
> able to use x264 for the better video quality at the same bitrate
> (since User Jobs remains a mystery to me), but suspect that encoding
> times would, as you note, become even more painful.

Most people who have tried to transocde HDTV mp2 recordings to mp4
have reported annoying audio sync problems after doing this.   This
is with mencoder which is used by myth's transcoder.

If you're getting it with perfect audio sync, I would be interested
to see your various flags and options to experiment with them.

My own transcodes have tended to be no-resize for 720p, and
resizing to either 1280x720p (with deinterlace) for 1080i, or
1280x540p (easy deinterlace here) because my tv is 1280x720 like
most TVs of the past couple of years.  (1080 line TVs are now
becoming more common.)

I haven't yet tried but might want to experiment with 1280x1080i,
with no deinterlace, but still throwing away the extra horizontal res
I can't see on my TV.

At any rate, I have found that when going to 1280x540, which is 75% of
the pixels on my TV, I can get quite decent visual transcodes in 1.5 gb
per hour, which is a nice compact data rate.   Even less than
your 2.76 gb/hour.

However, the audio has rarely been satisfactory.

My transcode times are not nearly as bad as yours though.
Don't forget to add the turbo option to the first pass if doing a 2-pass.
Frankly, the 1 pass transcodes aren't that bad.
>