[Ffmpeg-devel] [RFC] Musepack seeking patch

Kostya kostya.shishkov
Wed Dec 27 05:28:55 CET 2006


Here is a patch which enables full Musepack seeking.

As a side note: seeking may cause sound distortions because
Musepack stores scaling coefficients as difference to the
previous ones. libmppdec workarounds this by decoding
32 previous frames but that's a nasty hack and could not
be done here.
-------------- next part --------------
Index: libavformat/mpc.c
===================================================================
--- libavformat/mpc.c	(revision 7375)
+++ libavformat/mpc.c	(working copy)
@@ -71,6 +71,7 @@
     c->curframe = 0;
     c->lastframe = -1;
     c->curbits = 8;
+    c->frames_noted = 0;
 
     st = av_new_stream(s, 0);
     if (!st)
@@ -156,15 +157,42 @@
     return 0;
 }
 
+/**
+ * Seek to the given position
+ * If position is unknown but is within the limits of file
+ * then packets are skipped unless desired position is reached
+ *
+ * Also this function makes use of the fact that timestamp == frameno
+ */
 static int mpc_read_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags)
 {
     AVStream *st = s->streams[stream_index];
     MPCContext *c = s->priv_data;
+    AVPacket pkt1, *pkt = &pkt1;
+    int ret;
     int index = av_index_search_timestamp(st, timestamp, flags);
-    if (index < 0)
+    uint32_t lastframe;
+
+    /* if found, seek there */
+    if (index >= 0){
+        c->curframe = st->index_entries[index].pos;
+        return 0;
+    }
+    /* if timestamp is out of bounds, return error */
+    if(timestamp < 0 || timestamp >= c->fcount)
         return -1;
-    c->curframe = st->index_entries[index].pos;
-
+    /* seek to the furthest known position and read packets until
+       we reach desired position */
+    lastframe = c->curframe;
+    if(c->frames_noted) c->curframe = c->frames_noted - 1;
+    while(c->curframe < timestamp){
+        ret = av_read_frame(s, pkt);
+        if (ret < 0){
+            c->curframe = lastframe;
+            return -1;
+        }
+        av_free_packet(pkt);
+    }
     return 0;
 }
 



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