[Libav-user] Libavfilter - Dynamic filtergraph reconfiguration

[Paul B Mahol]

On Fri, Feb 5, 2021 at 2:49 AM ilkercan Kaya <canilkerkaya at gmail.com> wrote:

> enable option is also command for every filter that supports timeline. Yes
>> it looks like not documented explicitly.
>
> Does this mean that I can set "enable" as an option? if so I tried to do
> the following before initializing the filter:
>
> if ((res = av_opt_set_int(ctx, "enable", 1, AV_OPT_SEARCH_CHILDREN)) == 0) {
>     isOn = true;
> } else {
>     isFxBroken = true;
>     LOGE("AvFX::activateFilter failed! %s %s", name,
>          av_err2str(res));
> }
>
> But the call always landed on else with " AvFX::activateFilter failed!
> agate Invalid argument"
> Than I tried the following:
>
> if ((res = av_opt_set(ctx, "enable", "1", AV_OPT_SEARCH_CHILDREN)) == 0) {
>     isOn = true;
> } else {
>     isFxBroken = true;
>     LOGE("AvFX::activateFilter failed! %s %s", name,
>          av_err2str(res));
> }
>
> This time it did not land on else but this just makes it crash the app
> when data is passed through the filtergraph with "null pointer deference on
> libavfilter.so"
>
> How may I set this enable option through the code?
>

There is nothing wrong with your code. It is just bug in libavfilter, I
posted patch to fix it on devel mailing list.

There are two APIs to set options, one of them is not much tested and thus
it got broken.


>
> On Tue, Feb 2, 2021 at 12:52 AM Paul B Mahol <onemda at gmail.com> wrote:
>
>>
>>
>> On Mon, Feb 1, 2021 at 10:33 PM ilkercan Kaya <canilkerkaya at gmail.com>
>> wrote:
>>
>>> A simpler solution, if you only need to implement enabling and disabling
>>>> some of the filters, you can expect the "timeline" support does the
>>>> trick:
>>>
>>>
>>> I looked at timeline support, correct me if I am wrong but it is done
>>> through the *enable_str  *property of *AVFilterContext*. It is
>>> activated with *avfilter_init_str *call. This seems like setting the *enable_str
>>> * evaluation can only be done once without reiniting the whole graph.
>>> If this is the case, is there a way to  pass a custom variable to the
>>> expression so that I can switch it on or off? The case in the example at
>>> the documentation, smartblur is hardcoded to be activated between 10
>>> seconds to 3 minutes, in my case I can not foresee when the filter will be
>>> turned on/off.
>>>
>>
>> enable option is also command for every filter that supports timeline.
>> Yes it looks like not documented explicitly.
>>
>> Just tried it and works.
>>
>> mpv crowd_run_1080p50.y4m -vf "lavfi=[sendcmd=2.0 colorcorrect enable
>> 0,colorcorrect=saturation=0]"
>>
>>
>>>
>>> On Mon, Feb 1, 2021 at 11:10 PM Paul B Mahol <onemda at gmail.com> wrote:
>>>
>>>> lowpass, highpass and agate on master git version have both timeline
>>>> and command support.
>>>>
>>>> On Mon, Feb 1, 2021 at 7:39 PM ilkercan Kaya <canilkerkaya at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi Everyone,
>>>>>
>>>>> I am making a mobile music app where the user can add multiple
>>>>> different FXS at runtime to current playing music through a two dimensional
>>>>> pad with an effects header. I am using FFmpeg, libavfilter in C++ to add
>>>>> multiple FX to the audio.
>>>>>
>>>>> My problem is, the user can disable any of the FX's I am using at any
>>>>> time as they wish, the effects I use are agate, lowpass, highpass. The
>>>>> graph is:
>>>>>
>>>>> abuffer -> lowpass -> highpass -> agate -> aformat -> abuffersink.
>>>>>
>>>>> From time to time, I want to disable some of the following  lowpass,
>>>>> highpass, agate. So I thought I could just reconfigure the graph and
>>>>> basically get rid of links to fulfil my wish. I am not sure this is the
>>>>> right way to do it tho. I tried to dig online but all I could find was a
>>>>> thread from 2012 with no conclusion. Libavfilter documentation doesn't say
>>>>> anything about reconfigure or reset existing filtergraph (of that I could
>>>>> find).
>>>>>
>>>>> What would be the best way to do this?
>>>>>
>>>>> Thank you!
>>>>> _______________________________________________
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>>>>> Libav-user at ffmpeg.org
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>>>>>
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>>>>
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