使用QThread动态创建QImage帧到ffmpeg stdin

事实证明,我是部分正确和错误的。

1. ffmpeg有多个级别和数量的内部缓冲,具体取决于输入/输出格式、过滤器和编解码器:我只是没有创建足够的帧来看到这种情况发生;
2. 与QProcess的交互应该发生在创建它的线程中;
3. 因此,数据不能从不同的线程直接写入写通道,因此必须使用信号;
4. 当所有数据都已写入时,必须关闭写入通道(从其同一线程),以确保编码的完成;

考虑到上述情况,我只使用线程创建图像,然后用保存的每张图像的QByteArray发出信号;最后,在图像创建完成后,我等待实际完成(基于 showinfo 过滤器输出),以便实际考虑线程 已完成 在那一点上。在有多个作业的情况下,可以使用一些优化来排队进一步创建图像,但考虑到它可能不会显著提高性能,我更喜欢当前的方法。

这是修订后的代码,我用不同的格式进行了测试,它似乎按预期工作。

import re
from PyQt5 import QtCore, QtGui, QtWidgets

logRegExp = r'(?:(n:\s+)(?P<frame>\d+)\s).*(?:(pts_time:\s*)(?P<time>\d+.\d*))'

class Encoder(QtCore.QThread):
    completed = QtCore.pyqtSignal()
    frameDone = QtCore.pyqtSignal(object)
    imageReady = QtCore.pyqtSignal(object)
    def __init__(self):
        super().__init__()
        self.imageReady.connect(self.writeImage)
        self.queue = []

        self.process = QtCore.QProcess()
        self.process.setReadChannel(self.process.StandardError)
        self.process.finished.connect(self.processQueue)
        self.process.readyReadStandardError.connect(self.stderr)
        self.process.started.connect(self.start)

    def addJob(self, width=1280, height=720, frameCount=500, format='h264', *opts):
        self.queue.append((width, height, frameCount, format, opts))
        if not self.process.state():
            self.processQueue()

    def writeImage(self, image):
        self.process.write(image)
        self.imageCount += 1
        if self.imageCount == self.frameCount:
            self.process.closeWriteChannel()

    def processQueue(self):
        if not self.queue:
            return
        self.currentLog = ''
        self.lastFrameWritten = -1
        self.imageCount = 0
        self.width, self.height, self.frameCount, format, opts = self.queue.pop(0)
        args = [
            '-y', 
            '-f', 'png_pipe', 
            '-i', '-',
        ]
        if opts:
            args += [str(o) for o in opts]
        args += [
            '-an', 
            '-vf', 'showinfo',
            '/tmp/test.{}'.format(format), 
        ]
        self.process.start('ffmpeg', args)

    def stderr(self):
        self.currentLog += str(self.process.readAllStandardError(), 'utf-8')
        *lines, self.currentLog = self.currentLog.split('\n')
        for line in lines:
            match = re.search(logRegExp, line)
            if match:
                data = match.groupdict()
                self.lastFrameWritten = int(data['frame'])
                self.frameDone.emit(self.lastFrameWritten + 1)
            else:
                print(line)

    def run(self):
        font = QtGui.QFont()
        font.setPointSize(80)
        rect = QtCore.QRect(0, 0, self.width, self.height)
        for frame in range(1, self.frameCount + 1):
            img = QtGui.QImage(QtCore.QSize(self.width, self.height), 
                QtGui.QImage.Format_ARGB32)
            img.fill(QtCore.Qt.white)
            qp = QtGui.QPainter(img)
            qp.setFont(font)
            qp.setPen(QtCore.Qt.black)
            qp.drawText(rect, QtCore.Qt.AlignCenter, 'Frame {}'.format(frame))
            qp.end()
            ba = QtCore.QByteArray()
            buffer = QtCore.QBuffer(ba)
            img.save(buffer, 'PNG')
            self.imageReady.emit(ba)
        while self.lastFrameWritten < self.frameCount - 1:
            self.sleep(.5)
        self.completed.emit()


class Test(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        layout = QtWidgets.QVBoxLayout(self)
        self.startButton = QtWidgets.QPushButton('Start')
        layout.addWidget(self.startButton)

        self.frameLabel = QtWidgets.QLabel()
        layout.addWidget(self.frameLabel)

        self.encoder = Encoder()
        self.encoder.completed.connect(lambda: self.startButton.setEnabled(True))
        self.encoder.frameDone.connect(self.frameLabel.setNum)
        self.startButton.clicked.connect(self.create)

    def create(self):
        self.startButton.setEnabled(False)
        self.encoder.addJob()


if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    test = Test()
    test.show()
    sys.exit(app.exec_())