Capture and write float PCM samples in MP4 using Source Reader / Sink writer

I have a problem with the sink writer to write AAC samples to MP4 sink.

I capture 44.1k stereo float samples.

I use a  IMFTransform resampler to convert them into PCM 16bits stereo samples.

These samples are sent to the MPEG4 sink writer (configured to encode them to AAC samples).

I call WriteSample without problems but nothing is written to the file.

Regards,