API changes, most recent first:
+2021-04-27 - xxxxxxxxxx - lavc yyyyyyyyy - avcodec.h
+ Constified AVCodecParserContext.parser.
+
+2021-04-27 - xxxxxxxxxx - lavd yyyyyyyyy - avdevice.h
+ The av_*_device_next API functions now accept and return
+ pointers to const AVInputFormat resp. AVOutputFormat.
+
+2021-04-27 - xxxxxxxxxx - lavd yyyyyyyyy - avdevice.h
+ avdevice_list_input_sources and avdevice_list_output_sinks now accept
+ pointers to const AVInputFormat resp. const AVOutputFormat.
+
2021-04-27 - xxxxxxxxxx - lavf yyyyyyyyy - avformat.h
av_find_best_stream now uses a const AVCodec ** parameter
for the returned decoder.