[Libav-user] Creating Panned MP3 Clips

Sun Jan 1 18:20:04 EET 2023

On Sun, Jan 1, 2023 at 12:57 PM Paul B Mahol <onemda at gmail.com> wrote:

>
>
> On Sun, Jan 1, 2023 at 7:36 AM Andrew Randrianasulu <
> randrianasulu at gmail.com> wrote:
>
>>
>>
>> вс, 1 янв. 2023 г., 09:10 Terry Corbet <tcorbet at ix.netcom.com>:
>>
>>> I have recently discovered how to use the Audacity Envelope Tool to turn
>>> a standard stereo MP3 file into a modified one in which throughout the
>>> entire duration of the clip the apparent source of the sounds will
>>> traverse from left to right.
>>
>>
>> may be pan filter can do something by altering volumes of individual
>> channels but as far as I can see you can't change its parameters at runtime?
>>
>>
>> https://ffmpeg.org/ffmpeg-filters.html#Changing-options-at-runtime-with-a-command
>>
>> ====
>> Filter pan
>>   Remix channels with coefficients (panning).
>>     Inputs:
>>        #0: default (audio)
>>     Outputs:
>>        #0: default (audio)
>> pan AVOptions:
>>    args              <string>     ..F.A......
>> ===
>>
>> no T , as you can see (ffmpeg 5.1)
>>
>> I wonder if our software (cinelerra-gg, video editor, so a bit
>> heavyweight) can do this via built-in keyframing .. I'll ask on our
>> maillist.
>>
>>
> Nope, your software can't do it.
>
> Use ffmpeg's stereotools filter with asendcmd. Supports runtime changing
> of parameters.
>

Thanks for suggestion! Yes, fully automatic panning on variable length
clips probably not easy to automate in CinGG
(even in bath mode). But I opened said filter (stereotools) and apparently
I can set cingg plugin keyframes for its internal parameters ..

I do not think we have timeline support for ff filters, but does this
system offer any advantage in our case?

>
>
>>
>>
>> While I could use that workflow to
>>> manually perform the same transformation on multiple files, for my own
>>> use as well as to help other family members [who generally have limited
>>> computer skills] I want to automate that workflow.
>>>
>>> Over the past four days I have played as much catch-up on the many
>>> topics and toolkits which appear might permit me to engineer a software
>>> solution to this requirement.  As a newbie, I probably will not
>>> correctly summarize what I believe to be the possible tools and
>>> approaches, so please forgive any misuse to the correct terminology.  I
>>> hope/believe that I might be able to state my concepts/questions in a
>>> manner which will be most considerate of the time of those who
>>> participate in this mailing list and most quickly help me move closer to
>>> a good approach to the challenge.
>>>
>>> 01.  I have managed to download the libraries which are used for the
>>> maintenance of the ffmpeg, ffprobe and ffplay triumvirate of tools.
>>>
>>> 02.  I have managed to successfully build some sample C programs [taken
>>> from the doc\examples sub-directory and other miscellaneous snippets
>>> found by following the wonderful links from your Wiki] using the
>>> CodeBlocks IDE framework.
>>>
>>> 03.  I have squirreled my way through the parts of the Doxygen
>>> documentation which seem like they would be most apropos.
>>>
>>> What I did not discover was any functions or examples of what I assumed
>>> I would be needing to do, which essential would be to process the audio
>>> frames of the FrontLeft [FL]  and FrontRight [FR] channels of coming out
>>> of a stream of packets.  That caused me to think that perhaps I would
>>> find examples of that processing by searching the Audacity sources to
>>> learn when and how they use the ffmpeg libraries.  And somewhere between
>>> the Audacity and FFmpeg sites I stumbled upon some sources and some
>>> documentation concerning what I suppose are two reasonable libraries
>>> devoted to "resampling" -- soxr and swr.
>>>
>>> It was about at that point that I concluded that my modification of the
>>> sampled frames probably does not fall within the ambit of what is meant
>>> by resampling at all and that led to an investigation of what Nyquist
>>> was all about.  Wow, what a guy Mr. Dannenberg must be.  The 2007
>>> Nyquist Reference Manual is a jaw-dropping read.
>>>
>>> I think that is enough background/context.  Here's were I would
>>> appreciate any suggestions:
>>>
>>> A.  Would it be possible to accomplish the steps necessary to achieve
>>> the desired result just using ffmpeg.exe?  I imagine that, using the
>>> command line tool and an appropriate shell scripting language, it might
>>> be necessary to make multiple passes of the original .mp3 file and/or
>>> the two separate channels.  I am not concerned about that loss of
>>> throughput; it will always be far faster than any manual procedure.
>>>
>>> B.  Nonetheless, there are some advantages that would accrue from
>>> accomplishing the work entirely in an application .exe with a little GUI
>>> glitter to help the user be able to attempt some trial-and-error
>>> [preview] with slight changes in some of the parameters of the task
>>> depending upon the nature of the audio content and the manner in which
>>> the user will eventually play the output on different devices in
>>> different environments.  Since I will not have the capabilities for
>>> building an Envelope in the manner that Nyquist [Lisp] accomplishes
>>> that, can anyone point me to any sample code doing that in C with the
>>> eight ffmpeg .dll libraries?
>>>
>>> C.  Or -- and I appreciate that it is not fair to ask this of this mail
>>> group -- but I would appreciate any experience/advice as to whether the
>>> solution really ought to be accomplished by some scripting and/or macro
>>> facilities wrapped around Audacity?
>>>
>>> Thank you so much for the fantastic capabilities you have provided with
>>> the entire FFmpeg effort and for your patience in reading through my
>>> questions as the bell is about to strike on the New Year.
>>>
>>> _______________________________________________
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>>>
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>>>
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