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Old 12th October 2020, 02:25   #1  |  Link
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Join Date: Jun 2007
Location: Ann Arbor, MI
Posts: 124
How force a constant bit rate for audio created with ffmpeg?

I'm putting title pages between video clips and concatenating them together so I need all the clips to be the same. I am creating the title slides with:

fa=Tone(length=3.0, type="Silence", samplerate=22050, channels=2)
v=BlankClip(90, 960, 540, pixel_type="RGB24", fps=29.97).ConvertToYV12(matrix="rec709").AddAlphaPlane()
AudioDub(v, fa).Subtitle("This is a test", align=5, size=24)
I'm creating the .mp4 clip using ffmpeg with:
ffmpeg -i gsn_10.avs -b:a 128 gsn_10.mp4
if I use -b:a 128k or don't use that parameter at all, it becomes variable rate and I need constant rate. Using the -b:a 128 makes it constant, but the bit rate doesn't change.

MediaInfo gives: "Bit rate: 1 084 b/s" and all other clips have "Bit rate: 128 kb/s"

The bit rate is the only difference in the clips. When I concat them with:
ffmpeg -f concat -safe 0 -i render.txt -c copy highlight.mp4
I get a ton of "Non-monotonous DTS in output stream" errors.

The resulting .mp4 is 19+ hours long when I should be about 6 minutes.

So, is there a way to force a constant bit rate of 128kb in AviSynth or do I need to find another way to do that in ffmpeg.
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constant bit rate, ffmpeg audio

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