[FFmpeg-devel] Why the tag “DURATION” is a necessity in Matroska files?

[wm4]

On Mon, 19 Jun 2017 09:38:19 +0200
Tobias Rapp <t.rapp at noa-archive.com> wrote:

> On 19.06.2017 02:04, 21naown at gmail.com wrote:
> > Le 18/06/2017 à 00:57, Sasi Inguva a écrit :  
> >> Hi,
> >>
> >> I was the one who made that change. We needed a way to obtain individual
> >> stream durations from a  Matroska file without reading the entire file. I
> >> don't think it adds to the file size greatly (< 50 bytes) compared to the
> >> size of video and audio data, hence I didn't hide it under an option.
> >> However if u really need it I can add an option.
> >>  
> >
> > Hello,
> >
> > Yes the size required for the tag “DURATION” is insignificant, but it is
> > preferable to have a choice with this tag like mkvmerge partially does
> > (because by default “--enable-durations” is enabled, maybe because it is
> > a part of “statistics-tags”, but we can disable them with
> > “--disable-track-statistics-tags”) and because the end user and his
> > software do not require it.
> >
> > Yes if you can move the tag “DURATION” as an optional tag—so an argument
> > is needed to enable it, I will be grateful to you.  
> 
> I disagree to this tag writing being opt-in. It requires marginal 
> runtime and storage space resources to write a duration field. The 
> application used for playback might change or even a new version of the 
> same application might make use of the tag. So it would be better to 
> enable it by default.
> 
> And for the tag writing being opt-out: Maintaining code also has some 
> cost. As far as I understand this option would just be required for some 
> aesthetic reason, thus I don't think it's worth adding that maintenance 
> cost by implementing code to make this tag opt-out.

But there's also this argument that writing these tags is silly, and
that mkvmerge should never have started it. Instead, there should be
proper EBML elements for this.