[FFmpeg-devel] [PATCH] [RFC] avformat/options_table: do not merge sidedata by default

[Reimar Döffinger]

On 25.11.2013, at 17:33, wm4 <nfxjfg at googlemail.com> wrote:
> On Mon, 25 Nov 2013 14:45:50 +0100
> Nicolas George <george at nsup.org> wrote:
> 
>> Le primidi 1er frimaire, an CCXXII, Reimar Döffinger a écrit :
>>> if it gets lost, and I lost the "fight" against side data anyway, so it would
>>> be a silly place to start it again.
>> 
>> For what it's worth, I fully agree with your analysis against side data.
>> 
>> IMHO, creating files in a standard format but that are only playable by lavf
>> is worse than refusing to mux them altogether: if compatibility is not an
>> option, just use another format, one that has support of the corresponding
>> side data.

I think in most cases that is "none, unless you write your own". Muxing support for side-data in FFmpeg is abysmal as far as I can tell, at best you might get some basic metadata out, but I don't think anything (properly) supports palettes or flv size change (well, I think nut can just store the full thing? But I wouldn't say that counts, since FFmpeg will still be the only thing that can read it correctly, and even that only if it isn't an older version).

> I fully agree. So where's the valid use for "merged" side data, other
> than applications that work only on FFmpeg and not on Libav and thus
> are not packaged by some major distros?

I didn't think it through so I was wrong about a few things, but first:
You did understand my point that "refusing to mux" is exactly _not_ what FFmpeg/lavf does (the side data merging doesn't change anything in that regard)?
And since we have no API that would provide the information necessary to do this, I am actually certain that no application using FFmpeg does this.
However what I missed is that even with side data merging FFmpeg itself will still silently drop (possibly critical) side data, so this change neither helps nor hurts there. So I think I withdraw my objections, as long as it is still possible to enable.
I'd also point out though that files created with embedded merged metadata most likely will be playable just fine in most players/cases (and not just lavf/lavc!): most decoders are good enough at error resilience to just throw away any additional nonsense data.


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