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

[Tobias Rapp]

On 19.06.2017 10:28, wm4 wrote:
> 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.

If there are proper fields for it in the container and they are 
supported by most applications, then yes: it makes no sense to duplicate 
the value into some metadata tag.

Regards,
Tobias