Adds module MJPEG

cmd/ffmpeg/README.md

@@ -39,3 +39,5 @@
 - https://html5test.com/
 - https://trac.ffmpeg.org/wiki/Capture/Webcam
 - https://trac.ffmpeg.org/wiki/DirectShow
+- https://stackoverflow.com/questions/53207692/libav-mjpeg-encoding-and-huffman-table
+- https://github.com/tuupola/esp_video/blob/master/README.md

cmd/ffmpeg/ffmpeg.go

@@ -37,6 +37,7 @@ func Init() {
 		"h264/ultra": "-codec:v libx264 -g 30 -preset ultrafast -tune zerolatency",
 		"h264/high":  "-codec:v libx264 -g 30 -preset superfast -tune zerolatency",
 		"h265":       "-codec:v libx265 -g 30 -preset ultrafast -tune zerolatency",
+		"mjpeg":      "-codec:v mjpeg -force_duplicated_matrix 1 -huffman 0 -pix_fmt yuvj420p",
 		"opus":       "-codec:a libopus -ar 48000 -ac 2",
 		"pcmu":       "-codec:a pcm_mulaw -ar 8000 -ac 1",
 		"pcmu/16000": "-codec:a pcm_mulaw -ar 16000 -ac 1",