Re: [mythtv-users] Recording HDTV shows to DVD

Mon, 17 Jan 2005 04:56:27 -0800

The reason you haven't found it is that it's a lossy conversion. Most people who would want to archive an HDTV recording wouldn't want to downgrade it to SDTV (i.e. 720x480). Since you asked, a few clarifications:

Along the way I've discovered that HDTV broadcasts are
in a format called MPEG2-TS (transport stream) which
differs from other MPEG2 files.  Standard Myth tools
such as nuvexport do not handle MPEG2-TS streams.

MPEG-TS is basically a wrapper for an MPEG-PS. I believe it's got some additional packetization and other "Transport"-type doodads, but the actual video stream is the same.


Another wrinkle is that HDTV broadcasts are often
1920x1080i or 1280x720p, whereas the highest
resolution allowed on a standard DVD is 720x480, so
some resizing of the video will be necessary.  Extra
credit here for making an anamorphic DVD that retains
the 16:9 format of the original broadcast.
Big wrinkle. Basically, it's not high-def once it's 720x480. You will need to reencode the video to 720x480, losing quality to bother resizing and another encoding genloss. Also, it'll take oodles of cpu time... on a 2GHz machine, probably 5-10hours/hour for a good 2-pass encode.


HDTV streams carry AC3 audio, but DVDs have either AC3
or MPEG audio, so it may be necessary to create a
two-channel audio track for use on DVD-players without
builtin AC3 decoding.
No. AC3 is more or less a wrapper as well. Somone correct me if I'm a bit off on this, but MPEG audio in the DVD spec is MPEG1-LayerII. AC3 is MPEG2-LayerIII (a.k.a. MP3) if 2-channel. If 5.1, it's different. HDTV audio stream should be able to go through unmodified.


I have found several Linux programs which can handle
portions of the above, but nobody has yet created a
set of instructions for how to use them to archive a
broadcast to DVD.  Did I miss the "Ultimate Guide to
HDTV-DVD Recording" in my search?

Try avidemux for a fairly nice WYSIWYG cutting/transcoding program. Feel free to take notes and write said missing guide.... :)

-Cory

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
*************************************************************************

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