Memory leak in Intel QSV decoder

[Aleksoid1978]

Summary of the bug:
Memory leak on call avcodec_flush_buffers() when use h264_qsv decoder in Windows 10/11.

For ease of reproduction, I simply took the official example ​https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/qsv_decode.c and added a call to avcodec_flush_buffers(decoder_ctx) in the read/decode loop for every 10th packet.
For each call to avcodec_flush_buffers(), memory consumption increases.

Windows 11 24H2.
Intel UHD 730 with the latest drivers, no memory leak.
Intel HD 530 with the latest drivers, memory leak.

I agree that the Intel drivers are to blame here, but maybe something is missing in the code in ffmpeg?

[Aleksoid1978]

A possible solution, at least for me it works - instead of reinitializing the MFX decoder, just reset it.

[Aleksoid1978]

qsv_decode_flush_fix