Re: [Mjpeg-developer] mpeg2dec pgm output

[Steven M. S. <sms@2BSD.COM>]

Howdy -

> From: Matto Marjanovic <ma...@mi...>
> 
> Two comments:
> 
>   a)  "pgmtoy4m" should probably be renamed to something like "pgmpipetoy4m",
>        so that people don't mistakenly think that it operates on real PGM

	Hmmm, I'm not too crazy about that name (but then I wasn't thrilled with
	the one I selected either ;)).   It will handle real PGM data but
	what'll come out will be a candidate for the abstract art exhibition
	I suspect <g>

	Would a warning in the usage() be adequate to let folks know it might
	not be what they expect?

>   b)  Who maintains mpeg2dec?  It would really be much better to get working

	No one.  Andrew declared it dead/gone a long time ago (which is why
	the YUV4MPEG2 version of mpeg2dec is 0.2.1 rather than 0.3.x)

>        YUV4MPEG2 support back into mpeg2dec, since it's the only thing that
>        knows what the headers should really be.

	And even the video_out_yuv4m.c module did NOT have all the information
	needed to generate a complete header - thus even using the version 
	with "native" YUV4MPEG2 support you still had to supply/override
	the header values later in the toolchain.   The field order and
	sample aspect for example were left as "unknown" and "progressive".
	About the only field that was "correct" was the rate and even then 
	it wasn't right for 3:2 pulldown material (or so I recall someone 
	mentioning).

	Since "native" support meant that the fields needed to be specified
	manually later anyhow it seemed quite reasonable to simply 
	require/allow the user to explicitly set them in a separate utility
	(the UNIX way you know :-)).

>       Plus, "mpeg2dec | mpeg2enc" should be an identity function, no?  ;^)

	Not really - but you knew that ;)    

	There's usually a 'y4mscaler' stuffed inbetween the two to scale to
	a different resolution.

	I wanted a recent decoder was to decode/rescale/encode movies the
	Internet Archive did at 368x480 (some one gave them a bad piece of
	advice about using 368x480 instead of 352x480) into 352x480 so they
	can be burned out to CVD or DVD.

	Between the recent fixes to the encoder (the Altivec stuff works
	fabulously now) and the Altivec enabled decoder even a single cpu
	Powerbook does a very nice job of transcoding movies.

	The mpeg2dec maintainers were either never approached about including
	a y4m output module or if they were then for whatever reason they
	chose not to include it.   In the latter case I think maintaining a
	separate utility is preferable to a forked copy of mpeg2dec that
	needs to be maintained (unless you're volunteering that is :-))

	In any event I made changes yesterday to the default handling and
	now attempt to intuit the video norm based on frame height but only
	for those parameters not explicitly specified on the command line.

> ps:  I'll finally be catching up on digital video hacking,
> 	'cause I finished what I was working on[*] and I no longer
> 	have anything else to do.  Life is good.

	Welcome back to the land of the living! :-)

	Cheers,
	Steven Schultz