GitLab

Include hstack_qsv, vstack_qsv and xstack_qsv. They may accept input
streams with different sizes.

Examples:
$ ffmpeg -hwaccel qsv -hwaccel_output_format qsv -i input.mp4 \
-filter_complex "[0:v][0:v]hstack_qsv" -f null -

$ ffmpeg \
-hwaccel qsv -hwaccel_output_format qsv -i input.mp4 \
-hwaccel qsv -hwaccel_output_format qsv -i input.mp4 \
-hwaccel qsv -hwaccel_output_format qsv -i input.mp4 \
-hwaccel qsv -hwaccel_output_format qsv -i input.mp4 \
-filter_complex "[0:v][1:v][2:v][3:v]xstack_qsv=inputs=4:fill=0x000000:layout=0_0_1920x1080|w0_0_1920x1080|0_h0_1920x1080|w0_h0_1920x1080" \
-f null -
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>