I am writing here my solution, maybe someone can use it.
i've chenged my H.264 resolution, in adobe FMLE, following those settings:
I also paste here the text, maybe the link will be changed
With H.264 selected, click the settings icon next to the Video Format box.
In the Advanced Encoder Settings dialog box, configure any of the following settings:
Profile Select either the Baseline or Main profile.
The Baseline profile is commonly used in video conferencing, mobile applications, or other applications which operate with limited processing power, storage capacity, and bandwidth. The Main profile is appropriate for applications that broadcast media, such as network broadcasting, and requires 1.5% more processing power than the Baseline profile.
Level Flash Media Live Encoder supports all available levels. Here are some examples of the resolution and frame rate achieved with different levels:
Maximum resolution (width x height)
Frame rate (frames per second)
352 x 288
720 x 576
1280 x 720
1920 x 1088
Encoding with the H.264 codec is CPU-intensive. Adobe recommends that you select a level and video size that enables CPU usage to remain below 75% during encoding.
For more information on H.264 profiles and levels, see commonly available resources about the H.264 video codec, such as the ISO/IEC 14496-10 standard on the ISO website and Wikipedia.
Keyframe frequency The interval at which to insert keyframes. The default is 5 seconds, which means a keyframe is inserted every 5 seconds.