Is 'faststart' optimization really useful to .webm videos?

[bulgom]

Hello,

Is """moov atom""" — or whatever it's called in the case of .webm videos — at the top of WEBM video code, or at least: optimized, useful ?

After testing "MkClean (win32 v.0.8.7)" * on some video, to be played by a web page, I found no difference with the — same (of course) — video, but NOT-faststart-optimized.

* "MkClean" is a utility that's supposed to optimize .webm videos the same way (or about) .mp4 videos are optimized, by placing "moov atom" at the top of the code.

"MkClean" seems to work, though. Once open as plain text, the code contents is different than of the non optimized version of the same .webm file ; and the optimized file still works ;

so far so good. BUT: NOT optimized, it loads, starts playing and seeks just as fast (or slow, in case of a lousy connection), as the optimized test.

I followed the advice of https://rigor.com/blog/2016/02/optimizing-webm-video-for-faster-streaming-and-seeking (the information looked reliable to me / but I know nothing about .WEBM optimization...).

Reason of my question: with .mp4 videos, "moov atom at the top" is simply... crucial; needless to test a non optimized video: it'll just take "for ever" to start playing. OK;

now, WITH .WEBM, it's not so clear. Or... is it ? Or am I missing something?


Thanks (+ plz excuse my non native English)


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[raffriff42]

The WebM file structure is based on the Matroska media container, per WebM FAQ.

And FFmpeg does have an option for Matroska that's similar to 'faststart':

matroska - options

This muxer supports the following options:

reserve_index_space

By default, this muxer writes the index for seeking (called cues in Matroska terms) at the end of the file, because it cannot know in advance how much space to leave for the index at the beginning of the file. However for some use cases – e.g. streaming where seeking is possible but slow – it is useful to put the index at the beginning of the file.

It is possible index space is always reserved in WebM (since WebM is optimized for streaming), and that's why you don't see any difference.

[bulgom]

Hi,

Thanks for the answer.

Now, if

It is possible index space is always reserved in WebM (since WebM is optimized for streaming), and that's why you don't see any difference.

does that mean I never * have to — manually — optimize .webm files?

* Or in some cases only? And if so, when should I take care of it?

_________

BTW, I tested using "Pazera WebM Converter 1.1 64-bit" (because it's easy ...). I guess it places the "cue" info. at bottom; + the interface has no "cue (faststart)" option anyway, neither mention whatsoever, about optimization (unless I missed it?)...


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[sneaker]

I think the blog post explains it pretty well. You don't have to optimize anything. If there is anything to optimize in the first place depends on your muxing software. You can analyze your mkv's structure using mkvinfo.

[bulgom]

(...)You don't have to optimize anything. (...)

OK: that's precisely what I was wondering about; so: I guess I'll take your word for it ! Thanks.

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