Error converting to AAC with time_base of Fraction(1, 1000)

[daveisfera]

Overview

Converting to AAC with a time_base of Fraction(1, 1000) doesn't work

Expected behavior

Conversion would work regardless of time_base

Actual behavior

Reported length of the file is incorrect and the file doesn't play back correctly

Investigation

If you scale the time_base and the pts/dts values by 8, then the conversion works

(NOTE: requires the second commit from #1180 to be able to do this)

Reproduction

Run the following with and observe the error:

python3 convert_to_aac_error.py audio_test_long.mkv output_bad.m4a

Then run with the adjustment and it will work:

python3 convert_to_aac_error.py audio_test_long.mkv output_good.m4a y

With this file:
https://drive.google.com/file/d/1mlL51WHC4iiTa4ibiMsTNYNmjzV4005-/view?usp=sharing

import sys
from fractions import Fraction

import av

def _main():
    adjust = len(sys.argv) >= 4 and sys.argv[3] == "y"
    with av.open(sys.argv[1]) as in_container:
        in_stream = in_container.streams.audio[0]
        with av.open(sys.argv[2], "w") as out_container:
            print(in_stream.time_base, in_stream.codec_context.layout)
            out_stream = out_container.add_stream(
                "aac", rate=in_stream.rate, layout=in_stream.codec_context.layout.name
            )
            num_frames = 0
            num_packets = 0
            for frame in in_container.decode(in_stream):
                num_frames += 1
                if adjust:
                    frame.pts *= 8
                    frame.dts *= 8
                    frame.time_base = Fraction(1, 8000)
                if num_frames == 1:
                    print(
                        type(frame),
                        frame.sample_rate,
                        frame.pts,
                        frame.dts,
                        frame.time_base,
                        len(frame.planes),
                        frame.planes[0].buffer_size,
                    )
                for packet in out_stream.encode(frame):
                    num_packets += 1
                    out_container.mux(packet)

            print(num_frames, num_packets)

            for packet in out_stream.encode(None):
                num_packets += 1
                out_container.mux(packet)

            print(num_packets)


if __name__ == "__main__":
    _main()

Versions

• OS: Debian Bookworm
• PyAV runtime: 10.0.0

PyAV v10.0.0
library configuration: --prefix=/usr --extra-version=1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libglslang --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librist --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --disable-sndio --enable-libjxl --enable-pocketsphinx --enable-librsvg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-libplacebo --enable-librav1e --enable-shared
library license: GPL version 2 or later
libavcodec     59. 37.100
libavdevice    59.  7.100
libavfilter     8. 44.100
libavformat    59. 27.100
libavutil      57. 28.100
libswresample   4.  7.100
libswscale      6.  7.100

• PyAV build:
  Installed from the branch in the mentioned PR
• FFmpeg:
  N/A using the OS libraries without ffmpeg itself being installed

Research

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.

Additional context

ffmpeg has known issues with AAC output but this appears to be specific to PyAV because doing the conversion with ffmpeg directly works

[daveisfera]

Moved to maintained fork:
WyattBlue#11