要获取第一个视频流的帧，请执行以下操作：

container = av.open("My_Super_Video.mp4")
total_frames = container.streams.video[0].frames

你可以用Stream.frames属性得到流中的帧数。
图片来源：www.example.comhttp://docs.mikeboers.com/pyav/develop/api/stream.html#av.stream.Stream

老问题，但只回答了一部分。让我来回答第二个问题。
问题1：是否可以通过PyAV获得帧数？如果可以，如何获得？

import av

with av.open("My_Super_Video.mp4") as container:
    total_frames = container.streams.video[0].frames

问题2：在这种情况下，我会考虑使用另一个库来逐帧加载和处理视频。哪个库可以让我以最快的速度完成上述操作。我知道以下几个库，但不知道它们的比较结果如何：[...]

ImageIO timings:  0.497
PyAV timings:     0.908
MoviePy timings:  0.766
OpenCV timings:   0.766
OpenCV timings:   0.569 (no conversion to RGB)

• • ImageIO速度最快**;很简单。OpenCV很接近（慢14%），但前提是你能在BGR中进行处理。如果你必须在RGB中工作，那么转换成本会很高（慢54%）。🥵).

也就是说，它高度依赖于工作负载，您应该始终使用特定的设置进行基准测试。实际上，与您处理每帧所花费的时间相比，差异通常可以忽略不计。
下面是一些基准测试代码，供感兴趣的读者参考：

import cv2
import av
import imageio.v3 as iio
from moviepy.editor import VideoFileClip
from PIL import Image
from timeit import Timer

# create a test video (roughly 11 sec and sane encoding)
frames = iio.imread("imageio:cockatoo.mp4", plugin="pyav")
iio.imwrite("test_video.mp4", frames, plugin="pyav", codec="h264")

def iio_read():
    total_frames = iio.improps("test_video.mp4", plugin="pyav").shape[0]
    for idx, frame in enumerate(iio.imiter("test_video.mp4", plugin="pyav")):
        foo = Image.fromarray(frame)

        # Note: I will not print in the benchmark. This will skew the result
        # print("Frame: %d/%d ..." % (idx, total_frames))

def av_read():
    with av.open("test_video.mp4") as container:
        total_frames = container.streams.video[0].frames
        for frame in container.decode(video=0):
            foo = frame.to_image()

def moviepy_read():
    # Can not read frame_count
    for frame in VideoFileClip("test_video.mp4").iter_frames():
        foo = Image.fromarray(frame)

def cv2_read():
    cap = cv2.VideoCapture("test_video.mp4")
    
    total_frames = cap.get(cv2.CAP_PROP_FRAME_COUNT)
    success, frame = cap.read()
    idx = 0
    while success:
        frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
        foo = Image.fromarray(frame)
        success, frame = cap.read()
        idx += 1

def cv2_read2():
    cap = cv2.VideoCapture("test_video.mp4")
    
    total_frames = cap.get(cv2.CAP_PROP_FRAME_COUNT)
    success, frame = cap.read()
    idx = 0
    while success:
        foo = Image.fromarray(frame)
        success, frame = cap.read()
        idx += 1

repeats = 10
time_moviepy = min(Timer("moviepy_read()", globals=globals()).repeat(repeats, number=1))
time_cv2 = min(Timer("cv2_read()", globals=globals()).repeat(repeats, number=1))
time_cv2_no_convert = min(Timer("cv2_read2()", globals=globals()).repeat(repeats, number=1))
time_iio = min(Timer("iio_read()", globals=globals()).repeat(repeats, number=1))
time_av = min(Timer("av_read()", globals=globals()).repeat(repeats, number=1))

print(
f"""
ImageIO timings:  {time_iio:.3f}
PyAV timings:     {time_av:.3f}
MoviePy timings:  {time_moviepy:.3f}
OpenCV timings:   {time_cv2:.3f}
OpenCV timings:   {time_cv2_no_convert:.3f} (no conversion to RGB)
"""
)

软件包版本：

av==10.0.0
moviepy==1.0.3
Pillow==9.4.0
opencv-python==4.7.0.68
imageio==2.25.0