DXVA2 decoder: Don't crash when the width or height cannot be determined.

In that case, just refuse to decode using DXVA.
Update ffmpeg
Add support for RTMP protocol with librtmp parameters input style.
Do not round aspect ratio when one of its values exceed 255.

- Use the same limit everywhere for consistency.
- Add one missing cast to avoid possible overflow.
Add RTMP to the installer