all files contain mp2 audio and mpeg4video encoded with lavc, with keyint=25.
- mp41 has no b-frames and has pts only for I-frames - image is shown only when
	there are timestamps

- mp42 has no b-frames and pts for all frames - all plays fine
- mp42b has 1 b-frame patterns (IPBPB...) and pts for all frames because the pack size
	is very small (600 bytes) - plays fine
- mp43 has 1 b-frame patterns (IPBPB...) with 2048 pack size; some frames lack pts - image seems to go back
- mp44 has 2 b-frames patterns (IPBBPBB...) with 2048 pack size; some frames lack pts - image seems to go back