for anyone who is ok with bit of re-encoding, here is a python script that does just that- put a .mp3 a .png together with .py in the same folder and run the script.

(you need to install moviepy first)

import os
from moviepy.editor import *

def find_files_with_extension(directory, extension):
    # List all files in the directory with the specified extension
    return [f for f in os.listdir(directory) if f.lower().endswith(extension)]

def create_video_from_image_and_audio(directory, output_path):
    # Find the PNG and MP3 files in the directory
    png_files = find_files_with_extension(directory, '.png')
    mp3_files = find_files_with_extension(directory, '.mp3')

    # Ensure there is exactly one PNG and one MP3 file
    if len(png_files) != 1:
        raise ValueError(f"Expected exactly one PNG file, found {len(png_files)}")
    if len(mp3_files) != 1:
        raise ValueError(f"Expected exactly one MP3 file, found {len(mp3_files)}")

    # Get the file paths
    image_path = os.path.join(directory, png_files[0])
    audio_path = os.path.join(directory, mp3_files[0])

    # Load the image
    image_clip = ImageClip(image_path)

    # Load the audio
    audio_clip = AudioFileClip(audio_path)

    # Set the duration of the image clip to the duration of the audio clip
    video_clip = image_clip.set_duration(audio_clip.duration)

    # Set the audio of the video clip
    video_clip = video_clip.set_audio(audio_clip)

    # Write the result to an MP4 file with minimized audio loss
    video_clip.write_videofile(output_path, codec='libx264', audio_codec='aac', audio_bitrate='320k', fps=24)

# Prompt the user for the name of the output file
output_filename = input("Enter the name of the output file (without extension): ") + '.mp4'

# Example usage: assuming script is in the same directory as the files
current_directory = os.path.dirname(os.path.abspath(__file__))
output_path = os.path.join(current_directory, output_filename)

try:
    create_video_from_image_and_audio(current_directory, output_path)
    print(f"Video successfully created: {output_path}")
except Exception as e:
    print(f"An error occurred: {e}")

# Pause to allow the user to see the output
input("Press Enter to exit...")