[Libav-user] atempo filter in and out pts

Philippe CASTELL pcastell at free.fr
Mon Feb 1 02:09:14 EET 2021

Hello all,

I use libavfilter with the filter ÔÇťatempo", to make a program which is able to play and stretch the audio

And I would like to display the play position starting from the beginning to the end of the file, even if the user change the tempo

For now I have the pts for input frames, and pts for output frames

But the atempo filter has some kind of buffering between input and output, and I have not found any way to know how much bufferization is currently used

So from the output frame, I am not able to know at which position it corresponds in the input frame

If there a generic way to know from a filter graph, how much data has not been processed so far, because of the buffering ?

The problem is far worse if I chain a atempo filter with a loudnorm filter, more that 3 seconds of audio is needed in input to have something in output, so I cannot display a bar progression of the play

Thanks for your help and your answers


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