Linux 将原始 OpenCV 图像通过管道传输到 FFmpeg
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Pipe raw OpenCV images to FFmpeg
提问by BrianTheLion
Here's a fairly straightforward example of reading off a web cam using OpenCV's python bindings:
这是一个使用 OpenCV 的 python 绑定读取网络摄像头的相当简单的示例：
'''capture.py'''
import cv, sys
cap = cv.CaptureFromCAM(0) # 0 is for /dev/video0
while True :
if not cv.GrabFrame(cap) : break
frame = cv.RetrieveFrame(cap)
sys.stdout.write( frame.tostring() )
Now I want to pipe the output to ffmpeg as in:
现在我想将输出通过管道传输到 ffmpeg，如下所示：
$ python capture.py | ffmpeg -f image2pipe -pix_fmt bgr8 -i - -s 640x480 foo.avi
Sadly, I can't get the ffmpeg magic incantation quite right and it fails with
可悲的是，我无法完全正确地获得 ffmpeg 魔法咒语，并且它失败了
libavutil 50.15. 1 / 50.15. 1
libavcodec 52.72. 2 / 52.72. 2
libavformat 52.64. 2 / 52.64. 2
libavdevice 52. 2. 0 / 52. 2. 0
libavfilter 1.19. 0 / 1.19. 0
libswscale 0.11. 0 / 0.11. 0
libpostproc 51. 2. 0 / 51. 2. 0
Output #0, avi, to 'out.avi':
Stream #0.0: Video: flv, yuv420p, 640x480, q=2-31, 19660 kb/s, 90k tbn, 30 tbc
[image2pipe @ 0x1508640]max_analyze_duration reached
[image2pipe @ 0x1508640]Estimating duration from bitrate, this may be inaccurate
Input #0, image2pipe, from 'pipe:':
Duration: N/A, bitrate: N/A
Stream #0.0: Video: 0x0000, bgr8, 25 fps, 25 tbr, 25 tbn, 25 tbc
swScaler: 0x0 -> 640x480 is invalid scaling dimension
- The captured frames are definitely 640x480.
- I'm pretty sure the pixel order for the OpenCV image type (IplImage) is GBR, one byte per channel. At least, that's what seems to be coming off the camera.
- 捕获的帧绝对是 640x480。
- 我很确定 OpenCV 图像类型 (IplImage) 的像素顺序是 GBR，每个通道一个字节。至少，这似乎是从相机中消失的。
I'm no ffmpeg guru. Has anyone done this successfully?
我不是 ffmpeg 大师。有没有人成功地做到了这一点？
采纳答案by BrianTheLion
Took a bunch of fiddling but I figured it out using the FFmpeg rawvideo demuxer:
花了一堆摆弄，但我想通了使用 FFmpeg rawvideo demuxer：
python capture.py | ffmpeg -f rawvideo -pixel_format bgr24 -video_size 640x480 -framerate 30 -i - foo.avi
Since there is no header in raw video specifying the assumed video parameters, the user must specify them in order to be able to decode the data correctly:
由于原始视频中没有指定假定视频参数的标头，因此用户必须指定它们才能正确解码数据：
-framerateSet input video frame rate. Default value is 25.-pixel_formatSet the input video pixel format. Default value is yuv420p.-video_sizeSet the input video size. There is no default, so this value must be specified explicitly.
-framerate设置输入视频帧率。默认值为 25。-pixel_format设置输入视频像素格式。默认值为 yuv420p。-video_size设置输入视频大小。没有默认值，因此必须明确指定此值。
And here's a little something extra for the power users. Same thing but using VLC to stream the live output to the web, Flash format:
这里有一些额外的东西给高级用户。同样的事情，但使用 VLC 将实时输出流式传输到网络，Flash 格式：
python capture.py | cvlc --demux=rawvideo --rawvid-fps=30 --rawvid-width=320 --rawvid-height=240 --rawvid-chroma=RV24 - --sout "#transcode{vcodec=h264,vb=200,fps=30,width=320,height=240}:std{access=http{mime=video/x-flv},mux=ffmpeg{mux=flv},dst=:8081/stream.flv}"
Edit: Create a webm stream using ffmpeg and ffserver
编辑：使用 ffmpeg 和 ffserver 创建 webm 流
python capture.py | ffmpeg -f rawvideo -pixel_format rgb24 -video_size 640x480 -framerate 25 -i - http://localhost:8090/feed1.ffm
回答by hgabe
Took me an hour to figure out that by default, windows pipes are not binary. This causes some bytes (specifically newlines) to be modified/omitted, and the resulting video is slowly shifting because the frame size is not constant.
我花了一个小时才弄清楚默认情况下，Windows 管道不是二进制的。这会导致一些字节（特别是换行符）被修改/省略，并且生成的视频正在缓慢移动，因为帧大小不是恒定的。
To work this around, the modified python file:
为了解决这个问题，修改后的 python 文件：
"""
videoCapture.py
"""
import cv2, sys
import time
if sys.platform == "win32":
import os, msvcrt
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
cap = cv2.VideoCapture(0) # 0 is for /dev/video0
while True :
ret, frm = cap.read()
sys.stdout.write( frm.tostring() )
To test if piping the raw video is successful, use ffplay. Make sure you specify a higher framerate than what is coming from the pipe, otherwise the video will start to lag
要测试管道原始视频是否成功，请使用 ffplay。确保您指定的帧率高于来自管道的帧率，否则视频将开始滞后
python videoCapture.py | ffplay -f rawvideo -pix_fmt bgr24 -s 640x480 -framerate 40 -i -
回答by Matt W
Not sure if this is Mac OS-specific, or python3-specific, but I needed to cast the frame to a string in order for this to work for me, like so:
不确定这是 Mac OS 特定的还是 python3 特定的，但我需要将框架转换为字符串才能使其对我有用，如下所示：
sys.stdout.write(str(frame.tostring()))
回答by abhiTronix
I'm Kind of late, But my powerful VidGearPython Library automates the process of pipelining OpenCV frames into FFmpeg on any platform. Here's a basic python example:
我有点晚了，但是我强大的VidGearPython 库可以在任何平台上自动将 OpenCV 帧流水线化为 FFmpeg 的过程。这是一个基本的python示例：
# import libraries
from vidgear.gears import WriteGear
import cv2
output_params = {"-vcodec":"libx264", "-crf": 0, "-preset": "fast"} #define (Codec,CRF,preset) FFmpeg tweak parameters for writer
stream = cv2.VideoCapture(0) #Open live webcam video stream on first index(i.e. 0) device
writer = WriteGear(output_filename = 'Output.mp4', compression_mode = True, logging = True, **output_params) #Define writer with output filename 'Output.mp4'
# infinite loop
while True:
(grabbed, frame) = stream.read()
# read frames
# check if frame empty
if not is grabbed:
#if True break the infinite loop
break
# {do something with frame here}
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
# write a modified frame to writer
writer.write(gray)
# Show output window
cv2.imshow("Output Frame", frame)
key = cv2.waitKey(1) & 0xFF
# check for 'q' key-press
if key == ord("q"):
#if 'q' key-pressed break out
break
cv2.destroyAllWindows()
# close output window
stream.release()
# safely close video stream
writer.close()
# safely close writer
来源：https: //github.com/abhiTronix/vidgear/wiki/Compression-Mode: -FFmpeg#2-writegear-apicompression-mode-with-opencv-directly
You can check out VidGear Docsfor more advanced applications and features.
您可以查看VidGear Docs以获取更高级的应用程序和功能。
Hope that helps!
希望有帮助！
