Revise `decode_audio`, `decode_video` example #373

Job	Run time
rust_clippy_check_ubuntu	4m 48s
build_static_and_test_ubuntu (release/6.0, nightly, no valgrind)	5m 28s
docs_rs_check	52s
build_static_and_test_ubuntu (release/6.0, 1.70.0, no valgrind)	5m 29s
build_dynamic_and_test_windows_pre	5m 41s
rust_clippy_check_windows	2m 28s
build_static_and_test_ubuntu (release/6.1, nightly, valgrind)	1h 3m 21s
rustfmt_check (macos-latest)	20s
build_static_and_test_ubuntu (release/6.1, nightly, no valgrind)	5m 52s
rustfmt_check (windows-latest)	33s
build_static_and_test_ubuntu (release/6.1, 1.70.0, no valgrind)	5m 25s
rustfmt_check (ubuntu-latest)	14s
build_dynamic_and_test_windows (nightly)	2m 15s
build_dynamic_and_test_windows (1.70.0)	2m 27s
	1h 45m 13s

Provide feedback