Gstreamer，无法使用videomixer渲染本地视频

使用这个管道，我可以使用视频混合器播放两个相同的视频，但是当我播放两个不同的视频时，它会失败

gst-launch -e videomixer name=mix ! ffmpegcolorspace ! xvimagesink  \
   uridecodebin uri="file:///home/dtolj/projects/test1.mp4" ! decodebin2 ! videorate ! videoscale ! video/x-raw-yuv,width=320,height=180 ! videobox border-alpha=0 top=0 left=0 ! mix. \
   uridecodebin uri="file:///home/dtolj/projects/test2.mp4" ! decodebin2 ! videorate ! videoscale ! video/x-raw-yuv,width=320,height=180 ! videobox border-alpha=0 top=0 left=-320 ! mix. 

错误：

ERROR: from element /GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin1/GstDecodeBin2:decodebin22/GstQTDemux:qtdemux0: GStreamer encountered a general stream error.
    Additional debug info:
    qtdemux.c(3865): gst_qtdemux_loop (): /GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin1/GstDecodeBin2:decodebin22/GstQTDemux:qtdemux0:
    streaming stopped, reason not-negotiated
    ERROR: pipeline doesn't want to preroll.

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似乎我对视频解码了两次，我删除了

decodebin2

，而且gstreamer似乎对视频格式非常挑剔。也许我不应该太依赖uridecodebin，而应该尝试使用合适的解复用器