How do I set audio stream's frame_size?

[Jackiexiao]

Overview

I want to get AudioFrame with duration 20ms (160 samples / sample rate 8000 ) from a wavfile.

but with code

container = av.open('8k.wav')
for frame in container.decode(audio=0):
    print(frame.samples)

I get 2048 which is 0.256 ms

Research

• I found a stream_option in av.open docs but have no idea how to use it
• I found av.audio.codeccontext.AudioCodecContext.frame_size, but I don't know how to change it too (I get 0 when I print it)

I have done the following:

• Checked the PyAV documentation
• Searched on Google
• Searched on Stack Overflow
• Looked through old GitHub issues
• Asked on PyAV Gitter
• ... and waited 72 hours for a response.

[RenaKunisaki]

I'm also seeing frame_size set to zero. Bug?

[pengzhendong]

Not bug. It means variable frame size.

https://github.com/FFmpeg/FFmpeg/blob/30996b71950317feae506a8abf87af286f3cedd3/libavcodec/avcodec.h#L1045-L1051

Each submitted frame except the last must contain exactly frame_size samples per channel.
May be 0 when the codec has AV_CODEC_CAP_VARIABLE_FRAME_SIZE set, then the frame size is not restricted.