Unexpected warnings about bit_rate when converting audio

[daveisfera]

Overview

Thanks for the great work on pyav! I'm using it to convert PCM audio to AAC in memory to convert a stream. It's working but I'm seeing unexpected warnings about bit_rate

Expected behavior

Default bit_rate would work or setting the bit_rate to an expected value would not give a warning

Actual behavior

The default gives this error:

Too many bits 16384.000000 > 6144 per frame requested, clamping to max

Then setting bit_rate to 128 gives this error (and setting it to 128 * 1024 gives the same error as above):

Bitrate 128 is extremely low, maybe you mean 128k

Build report:
Using av==10.0.0 in a requirements.txt file

Investigation

These warnings are printed in ffmpeg code

Reproduction

Here's a piece of sample code that's reading the data from files instead of a stream but it shows the issue:

import audioop
import sys
from fractions import Fraction

import av
import numpy
from av.audio.frame import AudioFrame

AUDIO_SAMPLE_RATE = 8000


def _main():
    print("Initializing")
    fake_output = av.open("/tmp/_alaw_to_aac.mp4", "w")
    audio_transcoder = fake_output.add_stream("aac", rate=AUDIO_SAMPLE_RATE, bit_rate=128, layout="mono")
    audio_data = AudioFrame(format="s16", layout="mono", samples=160)
    audio_data.rate = AUDIO_SAMPLE_RATE
    audio_data.time_base = Fraction(1, AUDIO_SAMPLE_RATE)

    for n in range(1000):
        data = open("{}/sample-{:03d}.alaw".format(sys.argv[1], n), "rb").read()
        linear = audioop.alaw2lin(data, 2)
        array = numpy.frombuffer(linear, "i2")
        audio_data.planes[0].update(array)
        audio_data.pts = 20 * n

        aac = b""
        pts = 0
        for p in audio_transcoder.encode(audio_data):
            pts = p.pts
            aac += bytes(p)
        if aac:
            print("Size:", pts, len(aac))

    print("Done")


if __name__ == "__main__":
    _main()

Versions

• OS: Debian Bullseye
• PyAV runtime: 3.9.16
• PyAV build: 10.0.0 from pip
• FFmpeg: N/A (doesn't output anything so I believe I'm using what's included in the wheel

[daveisfera]

Is there a way to close this? Because it appears to be a bigger bug than just this warning (see #1088 )