video.set(cv2.CAP_PROP_POS_FRAMES, 25*30) 如何修改移动到视频最后一秒

在给定的`video.set(cv2.CAP_PROP_POS_FRAMES, 25 * 30)`这一行代码中，它使用了OpenCV库中的`cv2.VideoCapture`对象的`set`方法，来设置视频的帧位置。这里参数`cv2.CAP_PROP_POS_FRAMES`表示当前读取到的视频帧数，`25 * 30`通常代表25帧每秒的速度下播放30秒。

如果你想要移动到视频的最后一秒，你需要先获取视频的总帧数（total frames），然后计算最后一秒对应的帧数。假设视频总帧数为`frames_total`，你可以这样做：

# 获取视频的总帧数
frames_total = int(video.get(cv2.CAP_PROP_FRAME_COUNT))

# 计算最后一秒的帧数（假设视频帧率为FPS）
fps = video.get(cv2.CAP_PROP_FPS)
last_second_frames = fps

# 移动到最后一秒
video.set(cv2.CAP_PROP_POS_FRAMES, frames_total - last_second_frames)

在这个例子中，我们首先使用`cv2.CAP_PROP_FRAME_COUNT`获取总帧数，然后根据帧率计算出最后一秒的帧数，并将其从总帧数中减去，得到目标帧位置。

相关问题

如果一个视频很模糊，定位中间帧时定位不准vc.set(cv2.CAP_PROP_POS_FRAMES, round(middle_seconds*fps)) rval, frame = vc.read()，如何修改以上代码，模糊定位视频中间位置并截图

如果视频画面模糊，单纯依赖某一帧可能无法准确地定位中间位置。在这种情况下，可以尝试以下步骤来改善：

1. 首先，读取视频的前几帧作为参考，分析视频的整体清晰度变化趋势。这可以通过计算每一帧的均值或使用图像处理技术如Sobel算子检测边缘清晰度。

import cv2
import numpy as np

middle_seconds = ... # 计算出中间时间点
fps = vc.get(cv2.CAP_PROP_FPS)
total_frames = int(middle_seconds * fps)

# 初始化帧数计数和清晰度指标
frame_count = 0
best_frame_index = None
best_score = float('-inf')

while frame_count < total_frames:
    rval, frame = vc.read()
    if not rval:
        break
    
    # 使用边缘检测或其他算法评估当前帧的清晰度
    score = calculate_frame_clarity(frame)  # 自定义函数，返回清晰度评分

    if score > best_score:
        best_score = score
        best_frame_index = frame_count

middle_frame_index = best_frame_index

2. 然后，基于找到的最清晰的帧（`best_frame_index`），再读取对应的中间帧用于截图。

vc.set(cv2.CAP_PROP_POS_FRAMES, middle_frame_index)
rval, middle_frame = vc.read()

if rval:
    # 截图并保存中间清晰的帧
    fourcc = cv2.VideoWriter_fourcc(*'PNG')  # 或者其他图片格式如'.jpg'
    output_path = 'clear_middle_frame.png'
    cv2.imwrite(output_path, middle_frame)
else:
    print("Failed to read the clear middle frame.")

通过这种方法，虽然不能保证绝对精确，但应该能提高截图的质量，因为选择的是视频中最清晰的一帧。如果需要更精确，可以考虑对整个视频进行实时处理，动态寻找清晰度最高的帧。

import timefrom serial import Serialimport serial.tools.list_portsimport cv2import numpy as npcap1 = cv2.VideoCapture("/Users/yankaipan/Desktop/stand.mp4")cap2 = cv2.VideoCapture("/Users/yankaipan/Desktop/apple.mp4")cap3 = cv2.VideoCapture("/Users/yankaipan/Desktop/bamboo.mp4")cap4 = cv2.VideoCapture("/Users/yankaipan/Desktop/rubbish.mp4")port_list = list(serial.tools.list_ports.comports())port_list_1 = list(port_list[2])port_serial = port_list_1[0]arduinoData = serial.Serial(port_serial, 9600)time.sleep(1)while True: while (arduinoData.inWaiting() == 0): pass dataPacket = arduinoData.readline() dataPacket = dataPacket.decode().strip() print(dataPacket) time.sleep(3) if dataPacket == "a": while cap1.isOpened(): ret, frame = cap1.read() if ret == True: cv2.imshow('Frame', frame) if cv2.waitKey(25) & 0xFF == ord('q'): break else: cap1.set(cv2.CAP_PROP_POS_FRAMES, 0) elif dataPacket == "b": while cap2.isOpened(): ret, frame = cap2.read() if ret == True: cv2.imshow('Frame', frame) if cv2.waitKey(25) & 0xFF == ord('q'): break else: cap2.set(cv2.CAP_PROP_POS_FRAMES, 0) elif dataPacket == "c": while cap3.isOpened(): ret, frame = cap3.read() if ret == True: cv2.imshow('Frame', frame) if cv2.waitKey(25) & 0xFF == ord('q'): break else: cap3.set(cv2.CAP_PROP_POS_FRAMES, 0) elif dataPacket == "d": while cap4.isOpened(): ret, frame = cap4.read() if ret == True: cv2.imshow('Frame', frame) if cv2.waitKey(25) & 0xFF == ord('q'): break else: cap4.set(cv2.CAP_PROP_POS_FRAMES, 0)cv2.destroyAllWindows()怎样修改代码能够在其中一个a视频播放时，接收到arduino发送的消息时能够触发另一视频b或c或d并播放？

可以使用一个变量来记录当前正在播放的视频，当接收到新的消息时，根据消息内容判断应该播放哪个视频，并将当前正在播放的视频暂停或关闭，然后切换到新的视频播放。

以下是修改后的代码：

import time
from serial import Serial
import serial.tools.list_ports
import cv2
import numpy as np

cap1 = cv2.VideoCapture("/Users/yankaipan/Desktop/stand.mp4")
cap2 = cv2.VideoCapture("/Users/yankaipan/Desktop/apple.mp4")
cap3 = cv2.VideoCapture("/Users/yankaipan/Desktop/bamboo.mp4")
cap4 = cv2.VideoCapture("/Users/yankaipan/Desktop/rubbish.mp4")

port_list = list(serial.tools.list_ports.comports())
port_list_1 = list(port_list[2])
port_serial = port_list_1[0]
arduinoData = serial.Serial(port_serial, 9600)

time.sleep(1)

current_video = None  # 记录当前正在播放的视频

while True:
    while (arduinoData.inWaiting() == 0):
        pass
    dataPacket = arduinoData.readline()
    dataPacket = dataPacket.decode().strip()
    print(dataPacket)
    time.sleep(3)
    
    if dataPacket == "a":
        if current_video != cap1:  # 判断是否需要切换视频
            if current_video is not None:
                current_video.release()
            current_video = cap1
        while current_video.isOpened():
            ret, frame = current_video.read()
            if ret == True:
                cv2.imshow('Frame', frame)
                if cv2.waitKey(25) & 0xFF == ord('q'):
                    break
            else:
                current_video.set(cv2.CAP_PROP_POS_FRAMES, 0)
                
    elif dataPacket == "b":
        if current_video != cap2:
            if current_video is not None:
                current_video.release()
            current_video = cap2
        while current_video.isOpened():
            ret, frame = current_video.read()
            if ret == True:
                cv2.imshow('Frame', frame)
                if cv2.waitKey(25) & 0xFF == ord('q'):
                    break
            else:
                current_video.set(cv2.CAP_PROP_POS_FRAMES, 0)
                
    elif dataPacket == "c":
        if current_video != cap3:
            if current_video is not None:
                current_video.release()
            current_video = cap3
        while current_video.isOpened():
            ret, frame = current_video.read()
            if ret == True:
                cv2.imshow('Frame', frame)
                if cv2.waitKey(25) & 0xFF == ord('q'):
                    break
            else:
                current_video.set(cv2.CAP_PROP_POS_FRAMES, 0)
                
    elif dataPacket == "d":
        if current_video != cap4:
            if current_video is not None:
                current_video.release()
            current_video = cap4
        while current_video.isOpened():
            ret, frame = current_video.read()
            if ret == True:
                cv2.imshow('Frame', frame)
                if cv2.waitKey(25) & 0xFF == ord('q'):
                    break
            else:
                current_video.set(cv2.CAP_PROP_POS_FRAMES, 0)

cv2.destroyAllWindows()

注意，在切换视频时需要将上一个视频释放掉，否则会导致内存泄漏。