add_mux_stream does not work properly with matroska.

[caffeinism]

Hello. Thank you for the update. I tried to use the add_mux_stream method from yesterday’s update, but I’m getting an error when muxing a Matroska (.mkv) container. Below is the test code.

import av
import numpy as np
from fractions import Fraction

tb = Fraction(1, 24)
cc = av.CodecContext.create("libx264", "w")
cc.width = 1920
cc.height = 1080
cc.time_base = tb
cc.framerate = 1 / tb
cc.pix_fmt = "yuv420p"
cc.bit_rate = 6 * 1024 * 1024
frame = av.VideoFrame.from_ndarray(np.zeros((1080, 1920, 3), dtype=np.uint8))
with av.open("test.mkv", "w") as c:
    s = c.add_mux_stream("libx264", rate=24, width=640, height=640) # Since the shape can change, it doesn't matter...
    for i in range(24):
        frame.pts = i
        frame.time_base = tb
        for p in cc.encode(frame):
            p.stream = s
            c.mux(p)
    for p in cc.encode(None):
        p.stream = s
        c.mux(p)

If you change add_mux_stream to add_stream or convert the MKV file to MP4, this code will work without any issues.

When muxing MP4 files, an error occurs if the width and height are missing, so I tried to include as much information as possible, but nothing seemed to work.