The decoder initially read from the socket, decoded the video and sent
the decoded frames to the screen:
+---------+ +----------+
socket ---> | decoder | ---> | screen |
+---------+ +----------+
The design was simple, but the decoder had several responsabilities.
Then we added the recording feature, so we added a recorder, which
reused the packets received from the socket managed by the decoder:
+----------+
---> | screen |
+---------+ / +----------+
socket ---> | decoder | ----
+---------+ \ +----------+
---> | recorder |
+----------+
This lack of separation of concerns now have concrete implications: we
could not (properly) disable the decoder/display to only record the
video.
Therefore, split the decoder to extract the stream:
+----------+ +----------+
---> | decoder | ---> | screen |
+---------+ / +----------+ +----------+
socket ---> | stream | ----
+---------+ \ +----------+
---> | recorder |
+----------+
This will allow to record the stream without decoding the video.
The deprecated avcodec_decode_video2() should always the whole packet,
so there is no need to loop (cf doc/examples/demuxing_decoding.c in
FFmpeg).
This hack changed the packet size and data pointer. This broke recording
which used the same packet.
Some containers force their own time base. For example, matroska
overwrite time_base to (AVRational) {1, 1000}.
Therefore, rescale our packet timestamps to the output stream time base.
Barry