[Ffmpeg-devel] [PATCH] xan_dpcm in MPlayer + libavformat

[Diego Biurrun]

On Sat, Nov 18, 2006 at 03:20:24AM +0100, Michael Niedermayer wrote:
> 
> On Fri, Nov 17, 2006 at 05:17:58PM -0800, Mike Melanson wrote:
> > Diego Biurrun wrote:
> > >IIUC MPlayer falls back on codec_id if codec_tag is not set.  The
> > >problem is that these AVI files mark the xan_dpcm audio as 0x1 (or was
> > >it FourCC Axan + TwoCC 0x1 Roberto?), which is PCM.  I don't think there
> > >is a way to support this without hacks..
> > 
> > Right. The people (Origin) that developed this format never applied with 
> > Microsoft for a specific codec ID; they didn't mean for these files to 
> > be played in general media players. They have codec ID 0x0001 (usually 
> > reserved for PCM). There is data elsewhere in the AVI file indicating 
> > 'Axan'. All written up here:
> 
> AVCodecContext.stream_codec_tag i assume, and i would appreciate it if
> someone would remove this dirty "if video is xan then audio is so too"
> hack and instead add Axan to riff.c and check both stream_codec_id and
> codec_id

Dunno if I understood you correctly (probably not), but here is a patch
that contains the hack a bit more based on your suggestion to check
stream_codec_tag.  It's better than it was before at least.


BTW, some of the comments in that file seem misplaced.  Maybe someone
can fix them.

line 446:

    /* special case time: To support Xan DPCM, hardcode
     * the format if Xxan is the video codec */
    st->need_parsing = 1;


line 452
    /* force parsing as several audio frames can be in
       one packet */
    if (xan_video)
        st->codec->codec_id = CODEC_ID_XAN_DPCM;

Diego
-------------- next part --------------
Index: libavformat/avidec.c
===================================================================
--- libavformat/avidec.c	(revision 7117)
+++ libavformat/avidec.c	(working copy)
@@ -216,7 +216,6 @@
     int i, n;
     AVStream *st;
     AVIStream *ast = NULL;
-    int xan_video = 0;  /* hack to support Xan A/V */
     char str_track[4];
 
     avi->stream_index= -1;
@@ -432,8 +431,6 @@
                     st->codec->codec_type = CODEC_TYPE_VIDEO;
                     st->codec->codec_tag = tag1;
                     st->codec->codec_id = codec_get_id(codec_bmp_tags, tag1);
-                    if (st->codec->codec_id == CODEC_ID_XAN_WC4)
-                        xan_video = 1;
                     st->need_parsing = 2; //only parse headers dont do slower repacketization, this is needed to get the pict type which is needed for generating correct pts
 //                    url_fskip(pb, size - 5 * 4);
                     break;
@@ -443,16 +440,18 @@
                         av_log(s, AV_LOG_DEBUG, "invalid sample size or block align detected\n");
                     if (size%2) /* 2-aligned (fix for Stargate SG-1 - 3x18 - Shades of Grey.avi) */
                         url_fskip(pb, 1);
-                    /* special case time: To support Xan DPCM, hardcode
-                     * the format if Xxan is the video codec */
                     st->need_parsing = 1;
                     /* ADTS header is in extradata, AAC without header must be stored as exact frames, parser not needed and it will fail */
                     if (st->codec->codec_id == CODEC_ID_AAC && st->codec->extradata_size)
                         st->need_parsing = 0;
                     /* force parsing as several audio frames can be in
                        one packet */
-                    if (xan_video)
-                        st->codec->codec_id = CODEC_ID_XAN_DPCM;
+                    /* AVI files with Xan DPCM audio declare PCM in the
+                     * header but have Axan stream_code_tag */
+                    if (st->codec->stream_codec_tag == ff_get_fourcc("Axan")){
+                        st->codec->codec_id  = CODEC_ID_XAN_DPCM;
+                        st->codec->codec_tag = 0;
+                    }
                     break;
                 default:
                     st->codec->codec_type = CODEC_TYPE_DATA;