动态 GStreamer 管道不可搜索

Question

我有一个简单的 gstreamer 管道，可以播放 mp4 文件并支持搜索。我制作了这个管道的另一个版本，这个版本带有使用 typefind 元素动态创建的 demux。使用此版本的管道，查找似乎不起作用。以下是 Python 中这两个的最小版本：

管道图如下：

working/seekable版本：

dynamic/non-seekable版本：

请注意，实际播放在两个管道中都运行良好。只求在动态版本中不起作用。据我所知，两者之间唯一的主要区别是在动态管道中，将 typefind 连接到 demux 元素的 pad 处于拉模式，而在另一个中它们处于推模式，但我不知道这是不是相关的，如果是如何修复它。

另外一个区别是动态版中新创建的demux在seeking时处于playing状态，其他元素处于paused状态。我试过将新的多路分解器设置为暂停状态，但这似乎没有任何改变。

我能想到的代码的最小版本如下：

工作版本：

import gi
gi.require_version('Gst', '1.0')
gi.require_version('GLib', '2.0')
from gi.repository import Gst, GLib


def demux_pad_added(element, pad, pipeline):
    dec = pipeline.get_by_name('dec0')
    result = pad.link(dec.get_static_pad('sink'))
    if result != Gst.PadLinkReturn.OK:
        print('Could not link demux to dec.')
        exit(1)

    print('Linked demux to dec.')

    Gst.debug_bin_to_dot_file(pipeline, Gst.DebugGraphDetails.ALL, 'working')

    ret = pipeline.seek_simple(Gst.Format.TIME, Gst.SeekFlags.FLUSH | Gst.SeekFlags.KEY_UNIT, 1800 * Gst.SECOND)
    print('seek result:', ret)


def main():
    Gst.init(None)
    loop = GLib.MainLoop()

    pipeline = Gst.Pipeline()
    src = Gst.ElementFactory.make('filesrc', 'src0')
    typefind = Gst.ElementFactory.make('typefind', 'typefind0')
    demux = Gst.ElementFactory.make('qtdemux', 'demux0')
    dec = Gst.ElementFactory.make('libde265dec', 'dec0')
    sink = Gst.ElementFactory.make('appsink', 'sink0')

    src.set_property('location', 'foo.mp4')
    demux.connect('pad-added', demux_pad_added, pipeline)

    elements = [src, typefind, demux, dec, sink]

    for e in elements:
        pipeline.add(e)

    for i in range(0, len(elements) - 1):
        e1, e2 = elements[i], elements[i+1]
        if e1 == demux:
            continue
        if not e1.link(e2):
            print('Could not link {} to {}.'.format(e1.name, e2.name))
            exit(1)

    pipeline.set_state(Gst.State.PLAYING)
    loop.run()


if __name__ == '__main__':
    main()

seek无效的版本：

import gi
gi.require_version('Gst', '1.0')
gi.require_version('GLib', '2.0')
from gi.repository import Gst, GLib


def demux_pad_added(element, pad, pipeline):
    dec = pipeline.get_by_name('dec0')
    result = pad.link(dec.get_static_pad('sink'))
    if result != Gst.PadLinkReturn.OK:
        print(pad.name, dec.get_static_pad('sink').name)
        print('Could not link demux to dec.')
        exit(1)

    print('Linked demux to dec.')

    Gst.debug_bin_to_dot_file(pipeline, Gst.DebugGraphDetails.ALL, 'not-working')

    ret = pipeline.seek_simple(Gst.Format.TIME, Gst.SeekFlags.FLUSH | Gst.SeekFlags.KEY_UNIT, 1800 * Gst.SECOND)
    print('seek result:', ret)


def typefind_have_type(typefind, probability, caps, pipeline):
    videofmt = caps.to_string()
    if ',' in videofmt:
        videofmt = videofmt.split(',')[0]

    demux_name = {
        'video/quicktime': 'qtdemux',
        'video/x-matroska': 'matroskademux',
        'video/x-msvideo': 'avidemux',
    }.get(videofmt, None)

    if not demux_name:
        print('Unknown input file format: {}'.format(videofmt))
        exit(1)

    demux = Gst.ElementFactory.make(demux_name, 'demux0')
    pipeline.add(demux)
    demux.connect('pad-added', demux_pad_added, pipeline)
    demux.set_state(Gst.State.PLAYING)

    if not typefind.link(demux):
        print('Could not link typefind to demux.')
        exit(1)


def main():
    Gst.init(None)
    loop = GLib.MainLoop()

    pipeline = Gst.Pipeline()
    src = Gst.ElementFactory.make('filesrc', 'src0')
    typefind = Gst.ElementFactory.make('typefind', 'typefind0')
    demux = object() # dummy
    dec = Gst.ElementFactory.make('libde265dec', 'dec0')
    sink = Gst.ElementFactory.make('appsink', 'sink0')

    src.set_property('location', 'foo.mp4')
    typefind.connect('have-type', typefind_have_type, pipeline)

    elements = [src, typefind, demux, dec, sink]

    for e in elements:
        if e != demux:
            pipeline.add(e)

    for i in range(0, len(elements) - 1):
        e1, e2 = elements[i], elements[i+1]
        if e1 == demux or e2 == demux:
            continue
        if not e1.link(e2):
            print('Could not link {} to {}.'.format(e1.name, e2.name))
            exit(1)

    pipeline.set_state(Gst.State.PLAYING)
    loop.run()


if __name__ == '__main__':
    main()

如有任何帮助，我们将不胜感激。

Answer 1

我自己设法解决了这个问题。在将 typefind 链接到 demux 之后，我只需要将 demux.set_state(...) 调用移动到 typefind 回调的末尾。新的 typefind 回调现在看起来像这样：

def typefind_have_type(typefind, probability, caps, pipeline):
    videofmt = caps.to_string()
    if ',' in videofmt:
        videofmt = videofmt.split(',')[0]

    demux_name = {
        'video/quicktime': 'qtdemux',
        'video/x-matroska': 'matroskademux',
        'video/x-msvideo': 'avidemux',
    }.get(videofmt, None)

    if not demux_name:
        print('Unknown input file format: {}'.format(videofmt))
        exit(1)

    demux = Gst.ElementFactory.make(demux_name, 'demux0')
    pipeline.add(demux)
    demux.connect('pad-added', demux_pad_added, pipeline)
    #demux.set_state(Gst.State.PLAYING) # moved from here to further down

    if not typefind.link(demux):
        print('Could not link typefind to demux.')
        exit(1)

    demux.set_state(Gst.State.PLAYING) # <--- new location

动态 GStreamer 管道不可搜索

Dynamic GStreamer pipeline not seekable

python

gstreamer