Interlaced mpeg2 video with avenc_mpeg2video gstreamer

Question

The following GStreamer pipeline generates an mpeg2ts with an mpeg2 video track.

gst-launch-1.0 videotestsrc pattern=ball num-buffers=900 ! "video/x-raw, format=(string)I420, \
width=(int)704, height=(int)576, framerate=(fraction)25/1" ! avenc_mpeg2video ! \
mpegtsmux ! filesink location=test.ts

I need the video to be interlaced, but when adding the interlace component, I get:

gst-launch-1.0 videotestsrc pattern=ball num-buffers=900 ! "video/x-raw, format=(string)I420, \
width=(int)704, height=(int)576, framerate=(fraction)25/1" ! interlace ! avenc_mpeg2video ! \
mpegtsmux name=mux ! filesink location=test.ts
WARNING: erroneous pipeline: could not link interlace0 to avenc_mpeg2video0

Which is odd to me, as both components seem to support e.g. I420 on their pads. I've tried adding various capsfilters between interlace and avenc_mpeg2video, but to no avail - it just fails connecting in other ways. I believe the two should be compatible - can someone explain why the above fails and maybe even show what a working pipeline should look like?

Answer 1

Try to set alternate-scan parameter of avenc_mpeg2video to 1. There is no need to use the interlace component. This works for me with Gstreamer 1.19:

gst-launch-1.0 videotestsrc pattern=ball num-buffers=900 ! "video/x-raw, format=(string)I420, \
width=(int)704, height=(int)576, framerate=(fraction)25/1" ! avenc_mpeg2video alternate-scan=1 ! \
mpegtsmux ! filesink location=test.ts

You can check the parameters of avenc_mpeg2video with this command:

gst-inspect-1.0 avenc_mpeg2video