video mixer with PNG filesrc ERROR with nvvidconv


I have been trying to add png file (with alpha) to videomixer, the following code works but so slow and unusable.

48 ‘videomixer’, ‘name=mix’ , ‘!’, ‘autovideoconvert’, ‘!’, ‘omxh264enc’, ‘!’, ‘queue’, ‘!’, ‘muxer.’,
49 ‘filesrc’, ‘location=’+logo,
50 ‘!’, ‘image/png’,
51 ‘!’, ‘pngdec’,
52 //’!’, ‘imagefreeze’,
53 ‘!’, ‘videobox’, ‘border-alpha=0’, ‘top=0’, ‘left=0’,
54 ‘!’, ‘mix.’,
55 //‘videotestsrc’,
56 //’!’, ‘video/x-raw, format=(string)I420,width=(int)640, height=(int)360’,
57 //’!’, ‘videobox’, ‘border-alpha=0’, ‘top=0’, ‘left=0’,
58 //’!’, ‘mix.’,

but if we change autovideoconvert to nvvidconv, I got the following error

Inside NvxLiteH264DecoderLowLatencyInit
NvxLiteH264DecoderLowLatencyInit set DPB and Mjstreaming
ERROR: from element /GstPipeline:pipeline0/GstVideoMixer2:mix: At least one of the input pads contains alpha, but downstream can’t support alpha.

Additional debug info:
videomixer2.c(390): gst_videomixer2_update_converters (): /GstPipeline:pipeline0/GstVideoMixer2:mix:
Either convert your inputs to not contain alpha or add a videoconvert after the mixer

GStreamer error, exit code 0

is there any help?

I believe something similar to this was discussed last month: