[FFmpeg-devel] Re: [PATCH] avfilter: enhance command processing with chain propagation and direction control. (PR #20731)

[Zhao Zhili via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

> On Oct 31, 2025, at 03:12, Nicolas George via ffmpeg-devel <ffmpeg-devel@ffmpeg.org> wrote:
> 
> cenzhanquan1 via ffmpeg-devel (HE12025-10-21):
>> PR #20731 opened by cenzhanquan1
>> URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20731
>> Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20731.patch
>> 
>> The existing avfilter_process_command and avfilter_graph_send_command havelimitations in
>> command propagation: they only handle commands for individualfilters and lack the ability
>> to propagate commands through the entire filterchain, nor do they support directional
>> traversal of the filter graph. Thismakes it difficult to control multiple filters in a chain
>> (e.g., adjustingvolume for all related filters or enabling/disabling a series of filters)with
>> a single command.
> 
> You are proposing to add an API without adding any code that uses that
> API, let alone user-oriented examples. That makes it impossible to guess
> if the feature is useful or if there are better ways to achieve what you
> want it to do.

Current implementation isn’t a new API, but new flags. It extends the ways to
traverse a graph. 

The existing API has the capability to send commands to a specific filter, a certain
type of filter, or all filters, but it lacks the ability to send commands to a subgraph,
unless the user manually filters out all filters belonging to the subgraph, which is
possible but complex.

The newly added flags provide subgraph traversal capability.

A common use case is when a graph contains multiple sources; I want to send
commands, such as volume control, to a subgraph with a specific source as the
root node, without affecting other sources. While controlling via volume instance
names is also feasible, using the source for control offers additional flexibility.

> 
> Regards,
> 
> -- 
>  Nicolas George
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