Decoding timestamps do not increase monotonically

[matteo-agnelli]

Describe the bug

In order to proper package (for example, into mp4 files) the encoder output, the encoded frames are expected to be returned in increasing decode timestamp (DTS) order. This is, however, not happening. Or, to be more precise, it seems that DTSs are jumping backwards after a few frames.

To Reproduce

Encode some frames with the 'encoder_encode()' function and observe the values of the 'dts' field of the encoded frames.

Expected behavior

DTSs are expected to increase monotonically (no backwards jump).

Screenshots

PTSs/DTSs trend from a simple test:

Desktop (please complete the following information):

• Issues reproduced under MacOS 10.12/10.13, Microsoft Visual Studio 2015/2017 and Debian 9
• Encoder compiled with nasm 2.14