Convert an h264/mp3 video for DVD playback

[thetrueavatar]

Hello,
My wife has a private concert(h264/mp3 3.5 gb 1080p) she would like to convert to make it readable by dvd player.
Since I had to do some authoriting for the menu, I have used Nero Video.
This one allow me to add chapter, menu,... but has very few option for encoding. I found I could choose a VBR wich adapt to the target size but that was nearly all. Can't choose bitrate for audio encoding.
For this reason, I have used ffmpeg to encode manually video part with the following parameter:

ffmpeg -i input.avi -target pal-dvd -bf 2 -mbd rd -trellis 2 -cmp 2 -subcmp 2 -me_method epzs -threads 4 -vf zscale=w=720:h=576 -qscale:v 1 -aspect 16:9 output.mpg

I tought that with ffmpeg and qscale:v 1 I was doing kind of lossless encoding but to my surprised final size was only 2.7 gb while with nero I have filled the whole dvd. Is qscale:v 1 is well lossless ?
My oritginal file was in 1080p so I guess that the downscaling to 720x576 explain a part of the shrink(original was 3.5 gb in h264/mp3) but still I think it's a lot compare to the nero encoding which propose me around 6gb with Highest quality(8000kb/s).
here is the ouptut of ffmpeg

frame=146679 fps= 27 q=1.0 Lsize= 2783430kB time=01:37:47.12 bitrate=3886.4kbits/s speed=1.07x    
video:2398535kB audio:320857kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 2.354862%

I think that ffmpeg average bitrate is far under the nero encoder.
Is it a problem for dvd playback(does it need constant bitrate ??)
I wanted to use this file but nero seems to reencode it(didn't find a way to just copy it) but with a far less size than with direct nero encoding...
Is it possible to create the whole dvd structure with nero(including menu) and after replace video/audio file by the ffmeg encode ?