playbin3: it can't play some files if one track of the files can't be decoded, no matter it's audio track or video track. While playbin2 can.
For some files which include audio and video track, maybe one track can't work in some cases.
playbin3 fail to play those files, while playbin2 can do it.
For example, audio track of one file can't work when set format fail in gst_ffmpegauddec_set_format function by libav, and playbin3 will return directly. While playbin2 can still play the video track no matter the audio track can't work.