Videos: ffmpeg framerate (-r) option incorrect when using h264_nvenc

[abgd1234]

When NVENC is used, the call to ffmpeg sets the framerate to 30 before -i. This causes ffmpeg to interpret the input video as 30fps, even when it isn't.

photoprism/internal/ffmpeg/convert.go

Lines 81 to 86 in 4909f86

	case NvidiaEncoder:
	// ffmpeg -hide_banner -h encoder=h264_nvenc
	result = exec.Command(
	ffmpegBin,
	"-r", "30",
	"-i", fileName,

To fix this, "-r", "30", should be placed after "-i", fileName, in line with the other non-NVENC cases.

[lastzero]

This is generally intended to limit the size and bitrate of the transcoded version as 4K 60fps videos are HUGE, especially when using a less efficient encoder. We welcome a pull request to update the command so it meets that goal should this currently not be the case.

[abgd1234]

The issue is that the input file rather than the output file is specified as 30fps. For example, a 15fps input video will be treated as 30fps, and the transcoded output video will then run twice as fast. This is simply a bug - all the other encoder cases correctly place "-r", "30", after the input file.

I have submitted pull request #2449 to fix this.