Andrea,

I am starting to look at this also -- sorry I missed the conversation between you and Andrew and glad you included it here so I can try to follow.  I can at least confirm: "patch4" can be for sure deleted -- the ffmpeg-4.3 patch 4 was deleted from GIT on about 15 October 2020 and ffmpeg.git.patch4 should have been deleted then also.  I will update with progress as I get there but have not used the latest from Andrew yet and currently getting the following errors too:

ffmpeg.C:410:44: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:416:44: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:421:35: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:723:11: error: ‘AVStream’ {aka ‘struct AVStream’} has no member named ‘nb_index_entries’
ffmpeg.C:723:46: error: ‘AVStream’ {aka ‘struct AVStream’} has no member named ‘index_entries’
ffmpeg.C:2092:79: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:2128:71: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:2325:39: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:2333:38: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:2555:31: error: invalid conversion from ‘const AVInputFormat*’ to ‘AVInputFormat*’ [-fpermissive]
ffmpeg.C:2762:47: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:3008:35: error: ‘AVStream’ {aka ‘struct AVStream’} has no member named ‘codec’
ffmpeg.C:3008:10: error: ‘avcodec_copy_context’ was not declared in this scope; did you mean ‘avcodec_free_context’?
ffmpeg.C:3654:77: error: cannot convert ‘int*’ to ‘size_t*’ {aka ‘long unsigned int*’}
ffmpeg.C:3882:42: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:3888:42: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:3895:50: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
ffmpeg.C:4070:19: error: ‘AVStream’ {aka ‘struct AVStream’} has no member named ‘nb_index_entries’
ffmpeg.C:4073:27: error: ‘AVStream’ {aka ‘struct AVStream’} has no member named ‘index_entries’
fileffmpeg.C:162:71: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
fileffmpeg.C:193:71: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
fileffmpeg.C:1849:53: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
fileffmpeg.C:1887:53: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]