[mythtv-users] How much space should transcoding HDTV to mpeg4 save?

Brad Templeton brad+myth at templetons.com
Fri Jan 19 23:32:28 UTC 2007

On Thu, Jan 18, 2007 at 03:35:29PM -0500, Steven Adeff wrote:
> On 1/18/07, ryan patterson <ryan.goat at gmail.com> wrote:
> Depends on how much your willing to loose in quality.
> Basically, xvid will give you no size advantage over mpeg2 for HD
> recordings. mpeg4 (without h264) was not designed for larger
> resolution higher bitrate encodes, thats where h264 comes in. Now, the
> best way to save space without compromising quality is use an inverse
> telecine filter and reencode to mpeg2 at the same Q level as the
> original "frame", this should give you very little loss in quality
> while saving about 15% of file size.

Hmm, I've had much better luck than this.   Where I didn't have luck
was in getting proper sound sync.  I eventually gave up (last year)
but are you saying the transcoders can now finally get their sound sync
> One way to save space for 1080i broadcasts is to resize them to 720p,
> you won't notice much loss in detail because most 1080i broadcasts are
> noisy anyway.

I have found that since I have a 720P TV, converting 1080i to 1280x540 is
an interesting alternative.   You eliminate interlace issues by going to
540, and at 3/4 of the pixels it's quite close to 1280x720 in quality, which
again is all my TV can show, along with most TVs from 2006 and earlier.

And you can in fact generate tolerable video at 2gb/hour, which is a third or
less of the typical size of 1080i mpeg-2.   Though I would go a bit higher
than 2gb/hour if disk space is at a premium.  3gb/hour will do you quite
decently with h264.

If you can get the sound to work right, particularly if eliminating
commercials on the transcode.

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