[NUT-devel] a few things about nut.txt

[Rich Felker]

On Fri, Nov 24, 2006 at 01:34:44PM +0100, Michael Niedermayer wrote:
> > 3.) There is no explanation of what EOR actually means.
> 
> end of relevance pretty much marks the start of a gap in a stream (no video
> or no audio or no subtitles until the next keyframe) it is (with the
> exception of a EOR after the very last frame) AFAIK relatively nut specific
> (= will probably never be used by anyone)

It's absolutely needed for subitles or seeking performance will be
utterly abysmal. Consider a movie with 5 subtitles at 5minutes and 5
subtiles at 70 minutes and none in between (yes I actually have a
movie like this). We wouldn't have added it if it weren't actually
needed.

I would personally prefer to forbid EOR for audio and video for the
time being except as a marker of final frame duration. If we ever see
a need we could later allow them but it was never my intention to
create a system for ugly special nut-specific semantics.

> * nut files with EOR cannot be converted to other containers or more
>   correctly you cannot seek correctly in the resulting file

Not true.

> * converting non nut to nut will not contain EOR except for marking the
>   duration of the very last frame

It doesn't have to since these other containers suck and don't care
about being able to synchronize subtitles on seeking.

> * lav* does not support it (and i dont plan to change that), for lav*
>   gaps are not allowed, you will have to encode black/silence/no subs
>   keyframes (which require only negligible storeage anyway)

The nut muxer should automatically generate EOR for subtitles and not
use it anywhere else (except perhaps eof). Just repeating an 'empty'
subtitle every few seconds is an ugly hack.

> * EOR breaks the ability to cut and merge nut files by simply adding
>   and removing headers
> 
> personally i would drop EOR from nut for anything but the very last frame

I think you missed the whole part about it being absolutely essential
for subtitles and seeking...

Rich