Set the timebase to use for the output frames timestamps. It is mainly useful for testing timebase configuration.
It accepts in input an arithmetic expression representing a rational. The expression can contain the constants "AVTB" (the default timebase), "intb" (the input timebase) and "sr" (the sample rate, audio only).
The default value for the input is "intb".
Examples
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Set the timebase to 1/25:
settb=1/25
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Set the timebase to 1/10:
settb=0.1
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Set the timebase to 1001/1000:
settb=1+0.001
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Set the timebase to 2*intb:
settb=2*intb
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Set the default timebase value:
settb=AVTB