I tried to create a file with these flags -- producing both .mpg and .mp4 as output files.

Neither of the outputs were playable by mplayer nor vlc.

Mplayer, in particular, had the following to say:
MPlayer 1.0rc2-4.2.1 (C) 2000-2007 MPlayer Team
CPU: Dual Core AMD Opteron(tm) Processor 275 (Family: 15, Model: 33, Stepping: 2)
CPUflags: MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 1 SSE2: 1
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx SSE SSE2

Playing /meow/tmp/KU.mp4.
libavformat file format detected.
LAVF: no audio or video headers found - broken file?
RAWDV file format detected.
VIDEO: [DVSD] 720x480 24bpp 29.970 fps 0.0 kbps ( 0.0 kbyte/s)
==========================================================================
Requested video codec family [qdv] (vfm=dshow) not available.
Enable it at compilation.
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffdv] vfm: ffmpeg (FFmpeg DV decoder)
==========================================================================
==========================================================================
Opening audio decoder: [libdv] Raw DV Audio Decoder
Unknown/missing audio format -> no sound
ADecoder init failed :(
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
Cannot find codec 'dvaudio' in libavcodec...
ADecoder init failed :(
ADecoder init failed :(
Cannot find codec for audio format 0x56444152.
Read DOCS/HTML/en/codecs.html!
Audio: no sound
Starting playback...
VDec: vo config request - 720 x 480 (preferred colorspace: Planar 411P)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
VDec: using Planar 411P as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
SwScaler: reducing / aligning filtersize 1 -> 4
SwScaler: reducing / aligning filtersize 5 -> 4
SwScaler: reducing / aligning filtersize 1 -> 1
SwScaler: reducing / aligning filtersize 9 -> 8
[swscaler @ 0xd40780]SwScaler: BICUBIC scaler, from yuv411p to yuv420p using MMX2
[swscaler @ 0xd40780]SwScaler: using 4-tap MMX scaler for horizontal luminance scaling
[swscaler @ 0xd40780]SwScaler: using 4-tap MMX scaler for horizontal chrominance scaling
[swscaler @ 0xd40780]SwScaler: using 1-tap MMX "scaler" for vertical scaling (YV12 like)
[swscaler @ 0xd40780]SwScaler: 720x480 -> 720x480
VO: [xv] 720x480 => 720x480 Planar YV12 [fs]
AC EOB marker is absent pos=74
AC EOB marker is absent pos=64
AC EOB marker is absent pos=75
AC EOB marker is absent pos=65
AC EOB marker is absent pos=109
AC EOB marker is absent pos=64
AC EOB marker is absent pos=64
AC EOB marker is absent pos=65
AC EOB marker is absent pos=64
AC EOB marker is absent pos=81
AC EOB marker is absent pos=64
AC EOB marker is absent pos=64
AC EOB marker is absent pos=109
AC EOB marker is absent pos=68
AC EOB marker is absent pos=64
AC EOB marker is absent pos=64
AC EOB marker is absent pos=65
...