[FFmpeg-user] Problem with astats and adrawgraph

Paul B Mahol onemda at gmail.com
Tue Nov 26 15:26:34 EET 2019

On 11/26/19, Michael Koch <astroelectronic at t-online.de> wrote:
>>> Thanks for your suggestion. Adding -r 25 does indeed solve the problem.
>>> Although I don't understand why it is required. The input framerate is
>>> 25 and it's detected correctly when I use the simpler filter chain.
>> Ah, I know why this happens, you need to use settb=1/FPS filter after
>> vstack.
>> This happens because adrawgraph filter it order to not drop output
>> frames need to have same timebase as input audio. Otherwise you would
>> get different metadata values.
>> Also note that your FPS in this case is 48000/1024. ~= 46.xxx
> 48000 is the audio sample rate, but where does the 1024 come from?

>From astats i think.

> I have a new example with testsrc2 and anoisesrc. There is no input file
> required for reproducing.
> There are two graphs: The first one uses signalstats and drawgraph, and
> the second one uses astats and adrawgraph. The problem is that the two
> graphs don't advance with the same speed in X direction. Do you have an
> idea how to make them synchrone?The video width is the same in both
> cases, otherwise vstack wouldn't work.
> The speed of drawgraph is correct, 1 pixel per frame. The speed of
> adrawgraph is too fast.
> Other question: reset=1 in astats means that the calculation result is
> reset after each frame. But how does the filter know when a frame ends,
> if the input of this filter is only an audio signal?
> c://ffmpeg/ffmpeg -f lavfi -i testsrc2=size=hd1080:duration=10:rate=25
> -f lavfi -i anoisesrc=d=10:c=pink:r=48000 -lavfi
> [0]signalstats,drawgraph=m1=lavfi.signalstats.YAVG:mode=line:slide=scroll:min=0:max=255,settb=1/25[G1];[1]astats=metadata=1:reset=1,adrawgraph=m1=lavfi.astats.1.RMS_level:mode=line:slide=scroll:min=-90:max=0,settb=1/25[G2];[G1][G2]vstack,settb=1/25
> -r 25 -y test.mp4

Use asetnsamples, to change size of audio frame to match you video FPS.

> Michael
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