Re: [VCDImager Bugs/Devel] Suggestion/workaround?

[Andrew Stevens]

On Thursday 17 May 2001 10:10, you wrote:
> Sorry, I must have clicked the wrong mailto: link the first time:
>
>
> Hi Herbert,
>
> First of all, vcdimager rocks, it's the missing piece I've been waiting
> for, for so long, without the help of any windoze machines.
>
> There is a problem with a number of encoders in setting an
> MPEG2 header "SDE" properly.  I don't know ANYTHING about the MPEG2 file
> format specs, but I came across the problem because it effected me.  Here
> is a URL describing the problem, and offering a program to patch the
> problematic MPEG2 files (some good stream debug info too, also).


The info in this page is misleading  Actually it is the barfing players not 
the encoders that are broken.  However, the usage the encoders were making of 
the field *is* a bit questionable.

> http://www.geocities.com/eby_vdo/

To quote the MPEG-2 standard:

6.3.6 Sequence display extension

This specification does not define the display process.  The information in 
this extension does not affect the decoding process and *may be ignored by
decoders that conform to this specification*.

<My *italics*.  I.e. The SDE is considered as a *hint* to the decoder no more>

The relevant fields (display_horizontal_size and display_vertical size) are 
intended to define a rectangle within the decode image is to be displayed
either by clipping (smaller) or by padding with borders.  Thus values for
720x540 etc are perfectly legit (if a bit silly!).   

Of course it is more sensible and less likely to provoke firmware bugs in
players if an encoder does the sensible thing and sets display_vertical_size
identical to vertical_size from the sequence header etc.



> Unfortunately, the ($1000!) Media Cleaner + MPEG Charger has this problem,
> and of course I have a DVD player that is effected.  
Ooops ;-)
>Running this patching
> program fixes the mpeg files right up.

> Is there any chance you could incorporate this code into
> VCDImager?  VCDImager can obviously figure out the correct resolution from
> the header, could it simply put this information into this "SDE" field?

Andrew