Decode Teletext subtitles into fourcc 'RGBA', then convert the chroma to...

Decode Teletext subtitles into fourcc 'RGBA', then convert the chroma to fourcc 'YUVA' using video blending and encode YUVA into YUVP and SPU. To be sent to the muxer. However the last step fails. The data never arrives in the muxer.

The transcode_spu_process() only works OK when used with overlay to burn the subtitle in the video. This needs a complete rewrite in the direction of 'osdmenu' subtitles.