[mythtv-users] Capture to DV or "uncompressed" AVI instead of MPEG-PS?

[Robert Johnston]

On Apr 5, 2005 5:49 PM, Gregg Casillo <gcasillo at insightbb.com> wrote:

<snip />

> Does anybody encode to MPEG4, edit, then go to MPEG2/DVD? Is this a Bad Idea?

It's a Bad Idea, as every time you decode/encode with "Lossy" codecs
(like MPEG1/2/4), you gain artifacts and degrade the quality of the
signal. And going MPEG4->MPEG2, you get all kinds of things
("Blocking" from MPEG4 adding to Calculated Red Luma issues in MPEG2
and so on). Think of it like making a photocopy of a photocopy, or
"Dubbing" a recorded cassette.

The best option for editing is to capture raw, edit, then encode.
Alternatively, you can capture to a compressed format, and cut to a
keyframe, thereby making the "Recode" section the length between
keyframes and no more (For each cut), preserving the original
compression and not amplifying the artifacts.

This is what GOPEdit does (Partially, it cuts so you get
kffffiibbbbkffffiibbbbk|<cut>|kffffiibbbbkffffiibbbb, where k is a
keyframe, f is a forward-predicted frame, i is a both-ways
(intermediate) predicted frame, and b is a backwards-predicted frame).
It's actually breaking the MPEG stream in the very strictest sense,
but IIRC, the MPEG spec says scene changes should be on a keyframe,
and if they're not the MPEG stream is allowed to be modified.