currently, it just seems to say "failed" and gives no clue as to why it failed
In my particular case, I eventually found the following in the log
0015537: 9160: Encoders: CEncoderFilter::Open: Start
0015537: 9160: Encoders: CFFmpegTranscoder::Open: Start
0015537: 9160: Encoders: CFFmpegTranscoder::CreateOutputFormat: Start
0015537: 9160: Encoders: CFFmpegTranscoder::CreateOutputFormat: Finish (0 ms)
0015537: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Start
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Input video is 90090.09 FPS, AutoFPS 1, target FPS 90090.09
0015538: 9160: Encoders: CFFmpegTranscoder::AVLog: [h264_nvenc @ 000001E4FCCB9140] The encoder timebase is not set.
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Opening codec 'h264_nvenc' failed
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Input video is 90090.09 FPS, AutoFPS 1, target FPS 90090.09
0015538: 9160: Encoders: CFFmpegTranscoder::AVLog: [h264_qsv @ 000001E4FCCB8180] The encoder timebase is not set.
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Opening codec 'h264_qsv' failed
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Input video is 90090.09 FPS, AutoFPS 1, target FPS 90090.09
0015538: 9160: Encoders: CFFmpegTranscoder::AVLog: [libx264 @ 000001E4FCCB71C0] The encoder timebase is not set.
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Opening codec 'libx264' failed
0015538: 9160: Encoders: CFFmpegTranscoder::CreateVideoStream: Finish (0 ms)
0015538: 9160: Encoders: CFFmpegTranscoder::Open: Creating video stream failed
0015538: 9160: Encoders: CFFmpegTranscoder::Open: Finish (0 ms)
0015538: 9160: Encoders: CEncoderFilter::Open: Result:
0015538: 9160: Encoders: CEncoderFilter::Open: Finish (0 ms)
0015538: 9160: Playback: DShowVideoGraph::RenderForTranscoding: Finish (3 ms)
0015538: 9160: Playback: DShowVideoGraph::Render: Rendering success: 0
0015538: 9160: Playback: DShowVideoGraph::Render: Finish (1254 ms)
0015538: 9160: Encoders: CVideoConverterDX::BuildGraph: Rendering transcoding graph failed.
0015538: 9160: Encoders: CVideoConverterDX::BuildGraph: Finish (1432 ms)
exposing at least one of those error codes/messages to the end user would be better than nothing