demux_lavf: add a hack to work around other hacks

mplayer (and all forks) use a single FourCC field to map codecs. This is
what sh_video->format and sh_audio->format is used for. Basically it's a
key into the codecs.conf table to find out what decoder to use. (There's
only one video codec and one major audio codec left - both libavcodec.
But we still have to deal with mapping coming from non-libavformat
demuxers.)

It seems this causes some video codecs to fail, such as WV1F in AVI [1].
demux_lavf generally throws away the codec_tag from libavformat if the
codec is MPEG-in-AVI. There are probably other cases like this. Add a
hack to enforce passing the correct codec tag when only ffmpeg demuxers
and decoders involved.

Note: the sample [1] needs to be flipped. With --demuxer=avi, this is
done correctly, because unlike demux_lavf, the demuxer uses the FourCC
directly for the sh_video->format tag, and finds the correct codecs.conf
entry (which contains the flip flag). We could just add a "whitelist" of
codec tags which can be passed through to sh_video->format, but I don't
want to do that just for such an obscure format as the sample at hand.

Note 2: when demux_lavf is used, the AVCodecContext could be passed
directly to vd_ffmpeg/ad_ffmpeg. The code to convert to/from the
internal mplayer stream headers is probably still needed, as there are
non-ffmpeg demuxers and audio decoders.

[1] http://samples.mplayerhq.hu/V-codecs/WV1F/AVI/title2.avi

libmpcodecs/ad_ffmpeg.c

@@ -159,6 +159,8 @@ static int init(sh_audio_t *sh_audio)
     }
     lavc_context->request_channels = opts->audio_output_channels;
     lavc_context->codec_tag = sh_audio->format; //FOURCC
+    if (sh_audio->gsh->lavf_codec_tag)
+        lavc_context->codec_tag = sh_audio->gsh->lavf_codec_tag;
     lavc_context->codec_type = AVMEDIA_TYPE_AUDIO;
     lavc_context->codec_id = lavc_codec->id; // not sure if required, imho not --A'rpi
 

libmpcodecs/vd_ffmpeg.c

@@ -239,6 +239,8 @@ static int init(sh_video_t *sh)
     } else {
         avctx->pix_fmt = rawfmt;
     }
+    if (sh->gsh->lavf_codec_tag)
+        avctx->codec_tag = sh->gsh->lavf_codec_tag;
     avctx->stream_codec_tag = sh->video.fccHandler;
     avctx->idct_algo = lavc_param->idct_algo;
     avctx->error_concealment = lavc_param->error_concealment;

libmpdemux/demux_lavf.c

@@ -292,6 +292,8 @@ static void handle_stream(demuxer_t *demuxer, AVFormatContext *avfc, int i)
     int stream_id;
     AVDictionaryEntry *lang = av_dict_get(st->metadata, "language", NULL, 0);
     AVDictionaryEntry *title = av_dict_get(st->metadata, "title", NULL, 0);
+    // Work around collisions resulting from the hacks changing codec_tag.
+    int lavf_codec_tag = codec->codec_tag;
     // Don't use native MPEG codec tag values with our generic tag tables.
     // May contain for example value 3 for MP3, which we'd map to PCM audio.
     if (matches_avinputformat_name(priv, "mpeg") ||
@@ -320,6 +322,7 @@ static void handle_stream(demuxer_t *demuxer, AVFormatContext *avfc, int i)
         stream_type = "audio";
         priv->astreams[priv->audio_streams] = i;
         sh_audio->libav_codec_id = codec->codec_id;
+        sh_audio->gsh->lavf_codec_tag = lavf_codec_tag;
         wf = calloc(sizeof(*wf) + codec->extradata_size, 1);
         // mp4a tag is used for all mp4 files no matter what they actually contain
         if (codec->codec_tag == MKTAG('m', 'p', '4', 'a'))
@@ -403,6 +406,7 @@ static void handle_stream(demuxer_t *demuxer, AVFormatContext *avfc, int i)
         stream_type = "video";
         priv->vstreams[priv->video_streams] = i;
         sh_video->libav_codec_id = codec->codec_id;
+        sh_video->gsh->lavf_codec_tag = lavf_codec_tag;
         bih = calloc(sizeof(*bih) + codec->extradata_size, 1);
 
         if (codec->codec_id == CODEC_ID_RAWVIDEO) {
@@ -517,6 +521,7 @@ static void handle_stream(demuxer_t *demuxer, AVFormatContext *avfc, int i)
         stream_type = "subtitle";
         priv->sstreams[priv->sub_streams] = i;
         sh_sub->libav_codec_id = codec->codec_id;
+        sh_sub->gsh->lavf_codec_tag = lavf_codec_tag;
         sh_sub->type = type;
         if (codec->extradata_size) {
             sh_sub->extradata = malloc(codec->extradata_size);

libmpdemux/stheader.h

@@ -54,6 +54,9 @@ struct sh_stream {
     struct sh_video *video;
     struct sh_sub *sub;
 
+    // Work around other hacks.
+    int lavf_codec_tag;
+
     char *title;
     bool default_track;