[MPlayer-dev-eng] YUV4MPEG (not 2) seek

[Rik Snel]

Hello Alex,

This patch implements seek support for YUV4MPEG(1). (btw: why does your
framenumber start at 1 and not at 0, I didn't see immediately why mplayer
tried to seek to negative offsets while seeking back, it got me confused).

The problem with YUV4MPEG2 is that (formally) the FRAME header doesn't
have a fixed length. (possible solution for backseeking: keep a (one
second resolution) index to the previous frames) Maybe forward seeking
must be done by assuming a minimal FRAME length, then take a big step
forward rel_seek_frames*(minimal frame length), and then seek forward to
the next legal FRAME header. (there is, of course, a possibility that a
part of the YUV data is accidentally a valid FRAME header...)

Greetings,

Rik.

--------
Nothing is ever a total loss; it can always serve as a bad example.
-------------- next part --------------
diff -Naur main/libmpdemux/demux_y4m.c main.dev/libmpdemux/demux_y4m.c
--- main/libmpdemux/demux_y4m.c	Fri Dec 28 09:38:59 2001
+++ main.dev/libmpdemux/demux_y4m.c	Fri Dec 28 21:38:02 2001
@@ -200,6 +200,7 @@
 
 	sh->disp_w = y4m_si_get_width(priv->si);
 	sh->disp_h = y4m_si_get_height(priv->si);
+    	demuxer->seekable = 0;
     }
 
     sh->format = mmioFOURCC('Y', 'V', '1', '2');
@@ -218,12 +219,42 @@
     sh->ds=demuxer->video;
     demuxer->video->id=0;
 		
-    /* disable seeking, lazy */
-    demuxer->seekable = 0;
 
     printf("YUV4MPEG2 Video stream %d size: display: %dx%d, codec: %ux%u\n",
             demuxer->video->id, sh->disp_w, sh->disp_h, sh->bih->biWidth,
             sh->bih->biHeight);
+}
+
+int demux_seek_y4m(demuxer_t *demuxer, float rel_seek_secs, int flags) {
+    sh_video_t* sh = demuxer->video->sh;
+    y4m_priv_t* priv = demuxer->priv;
+    int rel_seek_frames = sh->fps*rel_seek_secs;
+    int size = 3*sh->disp_w*sh->disp_h/2;
+    off_t curr_pos = stream_tell(demuxer->stream);
+
+    if (priv->framenum + rel_seek_frames < 0) rel_seek_frames = -priv->framenum;
+
+    //printf("seektoframe=%d rel_seek_secs=%f seektooffset=%ld\n", priv->framenum + rel_seek_frames, rel_seek_secs, curr_pos + rel_seek_frames*(size+6));
+    //printf("framenum=%d, curr_pos=%ld, currpos/(size+6)=%f\n", priv->framenum, curr_pos, (float)curr_pos/(float)(size+6));
+    priv->framenum += rel_seek_frames;
+
+    if (priv->is_older) {
+        /* Well this is easy: every frame takes up size+6 bytes
+         * in the stream and we may assume that the stream pointer
+         * is always at the beginning of a frame.
+         * framenum is the number of the frame that is about to be
+         * demuxed (counting from ONE (see demux_open_y4m)) */
+        if (priv->framenum == 0) { //this is because framenum starts at 1
+            priv->framenum=1;
+	    rel_seek_frames++;
+	}
+        stream_seek(demuxer->stream, curr_pos + rel_seek_frames*(size+6));
+    } else {
+	    /* should never come here, because seeking for YUV4MPEG2 
+	     * is disabled. */
+	    printf("not yet implemented!\n");
+    }
+    return 0; 
 }
 
 void demux_close_y4m(demuxer_t *demuxer)
diff -Naur main/libmpdemux/demuxer.c main.dev/libmpdemux/demuxer.c
--- main/libmpdemux/demuxer.c	Fri Dec 28 17:53:20 2001
+++ main.dev/libmpdemux/demuxer.c	Fri Dec 28 21:35:45 2001
@@ -658,6 +658,7 @@
 int demux_seek_avi(demuxer_t *demuxer,float rel_seek_secs,int flags);
 int demux_seek_asf(demuxer_t *demuxer,float rel_seek_secs,int flags);
 int demux_seek_mpg(demuxer_t *demuxer,float rel_seek_secs,int flags);
+int demux_seek_y4m(demuxer_t *demuxer,float rel_seek_secs,int flags);
 int demux_seek_fli(demuxer_t *demuxer,float rel_seek_secs,int flags);
 void demux_seek_mov(demuxer_t *demuxer,float pts,int flags);
 
@@ -708,6 +709,9 @@
 
   case DEMUXER_TYPE_MOV:
       demux_seek_mov(demuxer,rel_seek_secs,flags);  break;
+
+  case DEMUXER_TYPE_Y4M:
+      demux_seek_y4m(demuxer,rel_seek_secs,flags);  break;
 
   case DEMUXER_TYPE_FLI:
       demux_seek_fli(demuxer,rel_seek_secs,flags);  break;