python - 如何使用带有 python 子进程模块或 gst-launch-1.0 命令的 gstreamer 接收字节流？

Question

我想通过使用带有 python 子进程模块的 gstreamer 来接收字节流。
现在我可以成功地使用 ffmpeg 拉取字节流。如下所示。

import cv2
import subprocess as sp


height = 714
width = 420
rtsp_url = 'rtsp://127.0.0.1:8554/video'

# command
command = ['ffmpeg',
            '-i', rtsp_url,
            '-f', 'rawvideo',
            '-s',str(width)+'*'+str(height),
            '-pix_fmt', 'bgr24',
            '-fflags', 'nobuffer',
            '-']

p = sp.Popen(command, stdout=sp.PIPE, bufsize=10**8)

while True:
    raw_image = p.stdout.read(width*height*3)
    image =  np.fromstring(raw_image, dtype='uint8')
    image = image.reshape((height,width,3)).copy()
    cv2.imshow('image', image)
    key = cv2.waitKey(20)

我想使用 gstreamer 命令而不是 ffmpeg。到目前为止，我已经实现了使用 gstreamer 命令行将字节流写入文件。

gst-launch-1.0 rtspsrc location=rtsp://127.0.0.1:8554/video latency=0 drop-on-latency=true ! rtph264depay ! video/x-h264, stream-format='byte-stream' ! filesink location=/home/name/stdout

但它不能将字节流输出到管道，所以终端不显示字节流，不像 ffmpeg 命令。如何更改此命令以通过管道输出字节流，以便我可以从管道中读取。
感谢您花时间为我解答!
这是 RTSP 流代码。

import cv2
import time
import subprocess as sp
import numpy as np


rtsp_url = 'rtsp://127.0.0.1:8554/video'
video_path = r'test.mp4'
cap = cv2.VideoCapture(video_path)

# Get video information
fps = int(cap.get(cv2.CAP_PROP_FPS))
width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
print('fps={}'.format(fps))

# command
command = ['ffmpeg',
            '-re',
            '-y',
            '-stream_loop', '-1',
            '-f', 'rawvideo',
            '-vcodec', 'rawvideo',
            '-pix_fmt', 'bgr24',
            '-s', "{}x{}".format(width, height),
            '-r', str(fps),
            '-i', '-',
            '-c:v', 'libx264',
            '-pix_fmt', 'yuv420p',
            '-preset', 'ultrafast',
            # '-flags2', 'local_header',
            '-bsf:v', "'dump_extra=freq=k'", 
            '-keyint_min', '60',
            '-g', '60',
            '-sc_threshold', '0', 
            '-f', 'rtsp',
            '-rtsp_transport', 'tcp',
            '-muxdelay', '0.1', 
            rtsp_url]

p = sp.Popen(command, stdin=sp.PIPE)

cnt = 0
t_start = time.time()
while (cap.isOpened()):
    t_cur = time.time()-t_start

    ret, frame = cap.read()
    if not ret:
        cnt += 1
        print("count: {}".format(cnt))
        cap = cv2.VideoCapture(video_path)
        continue

    p.stdin.write(frame.tobytes())

    cv2.imshow('real_time', frame)

    key = cv2.waitKey(20)
    if key == 27:
        p.terminate()
        break

Answer 1

我设法创建了一个适用于 Linux 的示例。
我无法模拟 RTSP 相机，所以我使用 MP4 文件作为输入。
在 Python 中使用 FFmpeg CLI 创建 MP4 输入文件(用于测试):

sp.run(shlex.split(f'ffmpeg -y -f lavfi -i testsrc=size={width}x{height}:rate=25:duration=100 -vcodec libx264 -pix_fmt yuv420p {input_file_name}'))

GStreamer 命令是: p = sp.Popen(shlex.split(f'{gstreamer_exe} --quiet filesrc location={input_file_name} ! qtdemux ! video/x-h264 ! avdec_h264 ! videoconvert ! capsfilter caps="video/x-raw, format=BGR" ! filesink location={stdout_file_name}'), stdout=sp.PIPE)

--quiet使用 GStreamer 是因为 GStreamer 将消息打印到标准输出。

filesrc location ... 用于读取 MP4 输入 - 用 RTSP 管道替换它。

videoconvert ! capsfilter caps="video/x-raw, format=BGR"将视频格式转换为原始 BGR。

filesink location=/dev/stdout将输出重定向到标准输出(在 Linux 中)。

代码示例:

import cv2
import numpy as np
import subprocess as sp
import shlex
from sys import platform

width = 714
height = 420

input_file_name = 'input.mp4'  # For testing, use MP4 input file instead of RTSP input.

# Build MP4 synthetic input video file for testing:
sp.run(shlex.split(f'ffmpeg -y -f lavfi -i testsrc=size={width}x{height}:rate=25:duration=100 -vcodec libx264 -pix_fmt yuv420p {input_file_name}'))

if platform == "win32":
    # stdout_file_name = "con:"
    # gstreamer_exe = 'c:/gstreamer/1.0/msvc_x86_64/bin/gst-launch-1.0.exe'
    raise Exception('win32 system is not supported')
else:
    stdout_file_name = "/dev/stdout"
    gstreamer_exe = 'gst-launch-1.0'

# https://stackoverflow.com/questions/29794053/streaming-mp4-video-file-on-gstreamer
p = sp.Popen(shlex.split(f'{gstreamer_exe} --quiet filesrc location={input_file_name} ! qtdemux ! video/x-h264 ! avdec_h264 ! videoconvert ! capsfilter caps="video/x-raw, format=BGR" ! filesink location={stdout_file_name}'), stdout=sp.PIPE)

while True:
    raw_image = p.stdout.read(width * height * 3)

    if len(raw_image) < width*height*3:
        break

    image = np.frombuffer(raw_image, dtype='uint8').reshape((height, width, 3))
    cv2.imshow('image', image)
    key = cv2.waitKey(1)

p.stdout.close()
p.wait()
cv2.destroyAllWindows()

更新:
根据您的 new question ，我设法创建了 RTSP 捕获示例:

import cv2
import numpy as np
import subprocess as sp
import shlex

width = 240
height = 160

rtsp_url = 'rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mp4'  # For testing, use public RTSP input.

gstreamer_exe = 'gst-launch-1.0'  # '/usr/bin/gst-launch-1.0'

# https://stackoverflow.com/questions/29794053/streaming-mp4-video-file-on-gstreamer
p = sp.Popen(shlex.split(f'{gstreamer_exe} --quiet rtspsrc location={rtsp_url} ! queue2 ! rtph264depay ! avdec_h264 ! videoconvert ! capsfilter caps="video/x-raw, format=BGR" ! fdsink'), stdout=sp.PIPE)

while True:
    raw_image = p.stdout.read(width * height * 3)

    if len(raw_image) < width*height*3:
        break

    image = np.frombuffer(raw_image, np.uint8).reshape((height, width, 3))
    cv2.imshow('image', image)
    key = cv2.waitKey(1)

p.stdout.close()
p.wait()
cv2.destroyAllWindows()