[FFmpeg-devel] [PATCH] avformat/flvenc: allow to write qualifying metadata as number

Gyan Doshi ffmpeg at gyani.pro
Tue Feb 14 14:51:24 EET 2023

On 2023-02-14 03:35 pm, Anton Khirnov wrote:
> Quoting Gyan Doshi (2023-02-11 12:02:51)
>> The FLV format can store metadata as numbers which are used and handled
>> by many streaming platforms.
>> Now, metadata values can be sent as AMF Number type if
>> 1) tag key starts with "num_"
>> 2) value is scanned and can be represented as a double.
>> Written tag will have "num_" prefix removed if written as AMF Number.
> Using the normal metadata dict for structured data seems hacky to me.
> Wouldn't it be better to add a private dict-type muxer option for this?

The numerical metadata, like other string meta in FLV can change during 
streaming, so it will be
reloaded and refreshed. Once you suggested to shift the loading metadata 
from file + reload options
to fftools, this was the way to identify such metadata, since format 
contexts and AVStream only support
one AVDictionary and entries will have to be commingled

And this isn't really structured data. We are re-encoding how some of it 
is stored. It is still inputted
by the user as strings. The prefix is a cheap hack to clearly identify 
such keys.

(The other option would be add AVDictionary value 'types' and all 
associated signalling and tooling,
which seems useful in the long run but overkill for this.)


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