ffmpeg: switch to codecpar

This commit is largely based on commit 15e84ed3 from Anton Khirnov
<anton@khirnov.net> which was previously skipped in bbf5ef9d.

There are still a bunch of things raising codecpar related warnings that
need fixing, such as:
- the use of codec->debug in the interactive debug mode
- read_ffserver_streams(): it's probably broken now but there is no test
- lowres stuff
- codec copy apparently required by bitstream filters

The matroska references are updated because they now properly forward
the field_order (previously unknown, now progressive).

Thanks to James Almer for fixing a bunch of FATE issues in this commit.

Signed-off-by: Clément Bœsch <clement@stupeflix.com>
Signed-off-by: James Almer <jamrial@gmail.com>

cmdutils.c

@@ -1993,7 +1993,7 @@ AVDictionary *filter_codec_opts(AVDictionary *opts, enum AVCodecID codec_id,
         codec            = s->oformat ? avcodec_find_encoder(codec_id)
                                       : avcodec_find_decoder(codec_id);
 
-    switch (st->codec->codec_type) {
+    switch (st->codecpar->codec_type) {
     case AVMEDIA_TYPE_VIDEO:
         prefix  = 'v';
         flags  |= AV_OPT_FLAG_VIDEO_PARAM;
@@ -2051,7 +2051,7 @@ AVDictionary **setup_find_stream_info_opts(AVFormatContext *s,
         return NULL;
     }
     for (i = 0; i < s->nb_streams; i++)
-        opts[i] = filter_codec_opts(codec_opts, s->streams[i]->codec->codec_id,
+        opts[i] = filter_codec_opts(codec_opts, s->streams[i]->codecpar->codec_id,
                                     s, s->streams[i], NULL);
     return opts;
 }