Yes, this is somewhat intentional.

I dropped the video frame rate down as 30fps isn't really needed to perform barcode scanning. It should be possible to use full frame rate data (iirc) as my frame callback will just tell GStreamer to get rid of the frame if it's busy.

However, as the GStreamer pipeline is threaded, running processor intensive code such as the barcode decoders can cause the images drawn to the display to get backed up. This is especially bad when the libdmtx code is run (it runs in its own thread and is limited to being run only twice a second as it's so processor intensive).

I'm certainly happy to hear ideas for improving the performance and perhaps not using GStreamer at all would be one option here (not to mention replacing libdmtx with something that's faster and more efficient).