python 调用ffmpeg使用usb摄像头录制视频，输出h264格式，自动获取摄像头的最佳帧率和最大画面尺寸

import subprocess
import re

def get_camera_info():
    # 使用 ffmpeg 获取摄像头信息
    cmd = ["ffmpeg", "-f", "v4l2", "-list_formats", "all", "-i", "/dev/video0"]
    result = subprocess.run(cmd, stderr=subprocess.PIPE, text=True)

    # 解析输出以获取最佳帧率和最大画面尺寸
    output = result.stderr
    frame_rates = []
    resolutions = []

    for line in output.split("\n"):
        # 获取帧率信息
        frame_rate_match = re.search(r"([0-9]+(\.[0-9]+)?) fps", line)
        if frame_rate_match:
            frame_rates.append(float(frame_rate_match.group(1)))

        # 获取分辨率信息
        resolution_match = re.search(r"([0-9]+)x([0-9]+)", line)
        if resolution_match:
            width = int(resolution_match.group(1))
            height = int(resolution_match.group(2))
            resolutions.append((width, height))

    best_frame_rate = max(frame_rates) if frame_rates else 30  # 如果未找到，默认为30fps
    max_resolution = max(resolutions, key=lambda x: x[0]*x[1]) if resolutions else (640, 480)  # 默认640x480

    return best_frame_rate, max_resolution

def record_video(output_file, duration):
    best_frame_rate, max_resolution = get_camera_info()
    width, height = max_resolution

    # 使用 ffmpeg 录制视频
    cmd = [
        "ffmpeg",
        "-f", "v4l2",
        "-framerate", str(best_frame_rate),
        "-video_size", f"{width}x{height}",
        "-i", "/dev/video0",
        "-t", str(duration),
        "-c:v", "libx264",
        "-preset", "fast",
        "-pix_fmt", "yuv420p",
        output_file
    ]

    subprocess.run(cmd)

# 调用示例
output_video_path = "output_video.mp4"
record_duration = 10  # 录制10秒
record_video(output_video_path, record_duration)

import subprocess

def record_video(output_filename="output.mp4", duration=10):
    # FFmpeg命令模板，根据实际情况调整
    ffmpeg_cmd = [
        "ffmpeg",
        "-f", "v4l2",       # 使用v4l2设备（通常用于USB摄像头）
        "-i", "/dev/video0", # 设备路径，根据你的系统可能不同，如/dev/video1等
        "-c:v", "libx264",   # 使用H264编码器
        "-vf", "scale=-2:720", # 自动调整宽度，保持高度为720，-2表示宽度自动计算以保持原始宽高比
        "-r", "30",         # 帧率，这里设为30fps
        "-t", str(duration), # 录制时长，单位秒
        output_filename     # 输出文件名
    ]
    
    try:
        # 执行FFmpeg命令
        subprocess.run(ffmpeg_cmd, check=True)
        print(f"Video recording completed and saved as {output_filename}")
    except subprocess.CalledProcessError as e:
        print(f"Error occurred while recording video: {e}")

# 调用函数录制视频
record_video()