GStreamer-从MP4文件生成音频波形

Question

I have a two-part question,

• 1) I have an MP4 file and want to generate it's audio waveform.

• 2) I have another MP4 file which has audio at channel [0] and channel [1]
  and a video track too, I want to generate waveforms for both channels as separate images.

How can I achieve both of the above by using GSteamer?

Answer 1

Is the raw audio in 16-bit or 32-bit format? What is the sample rate (44100 hz) and what is time duration?

Anyways assuming 44.1khz at 10 second duration... since you can't draw 44 thousand samples as pixel width so choose a final display size (eg: width = 800px and height = 600px) and do math :

//# is (samplerate / duration) / width...
(44100 / 10) / 800 = 551;

After reading first 2 values, you will jump ahead by 551 bytes and repeat until total of (.

So in your raw data starting from pos = 0; ...

• 1) Check this and next sample, then multiply their values together ( sample[pos] x sample[pos+1] ).

• 2) Take that result and divide by 65335 (maximum value of 16-bits or 2 bytes).
  That's the final value of your first sample or point.

• 3) Draw a line to fit according to image height ( eg: 600px) so if sample = 0.83 then:

  line_height = (600 x 0.83); //# gives 498 as line height
line_count += 1; //# add plus 1 to line count (stop when it reaches 800)

• 4) Skip ahead from position [pos] by +551 bytes and repeat step (1) until line_count == 800;