本文档说明

使用 OpenCV 的 VideoWriter 录制摄像头视频，了解编码格式选择，并实现视频文件回放。

前置准备

source ~/opencv-env/bin/activate

基础录制

使用 cv2.VideoWriter 将摄像头画面保存为视频文件：

import cv2
import time
import os

os.environ.setdefault('DISPLAY', ':0')

DEVICE_INDEX = 73
DURATION = 5  # 录制时长（秒）
OUTPUT = "record.mp4"

cap = cv2.VideoCapture(DEVICE_INDEX)
cap.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter_fourcc('M', 'J', 'P', 'G'))
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1280)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 720)
cap.set(cv2.CAP_PROP_FPS, 25)

w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

# 创建 VideoWriter
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
out = cv2.VideoWriter(OUTPUT, fourcc, 25.0, (w, h))

# 丢弃前几帧（让自动曝光稳定）
for _ in range(5):
    cap.read()

frames = 0
start = time.time()
print(f"Recording {DURATION}s to {OUTPUT}...")

while time.time() - start < DURATION:
    ret, frame = cap.read()
    if not ret:
        break
    out.write(frame)
    frames += 1

elapsed = time.time() - start
out.release()
cap.release()

size_mb = os.path.getsize(OUTPUT) / (1024 * 1024)
print(f"Done: {frames} frames / {elapsed:.1f}s / {size_mb:.1f}MB")

编码格式说明

FourCC	格式	文件后缀	说明
mp4v	MPEG-4	.mp4	通用兼容，CPU 软编码
XVID	MPEG-4	.avi	兼容性好
MJPG	Motion JPEG	.avi	每帧独立压缩，文件较大

TIP

pip 安装的 OpenCV 只支持 CPU 软编码。如需硬件加速编码（文件更小、不占 CPU），参考 硬件加速进阶。

边录边显示

同时在屏幕上显示画面并录制：

import cv2
import time
import os

os.environ.setdefault('DISPLAY', ':0')

DEVICE_INDEX = 73
DURATION = 10
OUTPUT = "record_display.mp4"

cap = cv2.VideoCapture(DEVICE_INDEX)
cap.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter_fourcc('M', 'J', 'P', 'G'))
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1280)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 720)

w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

fourcc = cv2.VideoWriter_fourcc(*'mp4v')
out = cv2.VideoWriter(OUTPUT, fourcc, 25.0, (w, h))

win = "Recording"
cv2.namedWindow(win, cv2.WINDOW_NORMAL)
cv2.setWindowProperty(win, cv2.WND_PROP_FULLSCREEN, cv2.WINDOW_FULLSCREEN)

for _ in range(5):
    cap.read()

frames = 0
start = time.time()
print(f"Recording + Display for {DURATION}s... Press 'q' to stop early")

while time.time() - start < DURATION:
    ret, frame = cap.read()
    if not ret:
        break

    frames += 1
    elapsed = time.time() - start
    fps = frames / elapsed if elapsed > 0 else 0

    # 叠加录制状态
    cv2.putText(frame, f"REC {elapsed:.1f}s | FPS: {fps:.1f}", (10, 30),
                cv2.FONT_HERSHEY_SIMPLEX, 0.8, (0, 0, 255), 2)

    cv2.imshow(win, frame)
    out.write(frame)

    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

out.release()
cap.release()
cv2.destroyAllWindows()

size_mb = os.path.getsize(OUTPUT) / (1024 * 1024)
print(f"Saved: {OUTPUT} ({frames} frames, {size_mb:.1f}MB)")

性能提示

OpenCV 边录边显示时帧率约 14fps（1280×720），因为 CPU 同时负责编码和渲染。如需满帧录制+显示，使用 硬件加速的 GStreamer tee 方案。

视频回放

播放已录制的视频文件：

import cv2
import os

os.environ.setdefault('DISPLAY', ':0')

VIDEO_FILE = "record.mp4"

cap = cv2.VideoCapture(VIDEO_FILE)
if not cap.isOpened():
    print(f"Error: Cannot open {VIDEO_FILE}")
    exit()

fps = cap.get(cv2.CAP_PROP_FPS)
total = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
print(f"Playing: {VIDEO_FILE} ({w}x{h}, {fps:.1f}fps, {total} frames)")

win = "Playback"
cv2.namedWindow(win, cv2.WINDOW_NORMAL)
cv2.setWindowProperty(win, cv2.WND_PROP_FULLSCREEN, cv2.WINDOW_FULLSCREEN)

delay = int(1000 / fps) if fps > 0 else 33

while True:
    ret, frame = cap.read()
    if not ret:
        break

    cv2.imshow(win, frame)
    if cv2.waitKey(delay) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()
print("Playback finished")

VideoWriter API 速查

参数	说明
filename	输出文件路径
fourcc	编码格式，用 cv2.VideoWriter_fourcc(*'mp4v') 创建
fps	帧率（建议与摄像头一致）
frameSize	分辨率元组 (width, height)

out = cv2.VideoWriter("output.mp4", cv2.VideoWriter_fourcc(*'mp4v'), 25.0, (1280, 720))
out.write(frame)   # 写入一帧
out.release()      # 完成录制，关闭文件