MJPEG codec needs to control its -qmin and -qmax values

[alvestrand]

The following gave an error:

/usr/local/google/home/hta/code/compare-codecs/tools/ffmpeg -loglevel warning -s 1920x1080 -i video/mpeg_video/Kimono1_1920x1080_24.yuv -codec:v mjpeg -qmin 58 -b:v 2500k -y /usr/local/google/home/hta/code/compare-codecs/workdir/mjpeg/c0a4fd36dd74/2500/Kimono1_1920x1080_24.mjpeg

Error message:

[rawvideo @ 0x2d792e0] Estimating duration from bitrate, this may be inaccurate [swscaler @ 0x2d650a0] deprecated pixel format used, make sure you did set range correctly [mjpeg @ 0x2d7bac0] qmin and or qmax are invalid, they must be 0 < min <= max Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

Likely, qmin is larger than the default value for qmax.

[alvestrand]

Fixed in #51

[alvestrand]

51 submitted.