Add more resilience in reading ffm files. In particular, don't assume

that the write pointer is correct. This can happen in certain failure
modes.

Originally committed as revision 2524 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/ffm.c

@@ -51,6 +51,8 @@ typedef struct FFMContext {
     uint8_t packet[FFM_PACKET_SIZE];
 } FFMContext;
 
+static int64_t get_pts(AVFormatContext *s, offset_t pos);
+
 /* disable pts hack for testing */
 int ffm_nopts = 0;
 
@@ -64,6 +66,9 @@ static void flush_packet(AVFormatContext *s)
     fill_size = ffm->packet_end - ffm->packet_ptr;
     memset(ffm->packet_ptr, 0, fill_size);
 
+    if (url_ftell(pb) % ffm->packet_size) 
+        av_abort();
+
     /* put header */
     put_be16(pb, PACKET_ID);
     put_be16(pb, fill_size);
@@ -202,6 +207,8 @@ static int ffm_write_header(AVFormatContext *s)
     /* init packet mux */
     ffm->packet_ptr = ffm->packet;
     ffm->packet_end = ffm->packet + ffm->packet_size - FFM_HEADER_SIZE;
+    if (ffm->packet_end < ffm->packet)
+        av_abort();
     ffm->frame_offset = 0;
     ffm->pts = 0;
     ffm->first_packet = 1;
@@ -330,6 +337,8 @@ static int ffm_read_data(AVFormatContext *s,
             frame_offset = get_be16(pb);
             get_buffer(pb, ffm->packet, ffm->packet_size - FFM_HEADER_SIZE);
             ffm->packet_end = ffm->packet + (ffm->packet_size - FFM_HEADER_SIZE - fill_size);
+            if (ffm->packet_end < ffm->packet)
+                av_abort();
             /* if first packet or resynchronization packet, we must
                handle it specifically */
             if (ffm->first_packet || (frame_offset & 0x8000)) {
@@ -363,6 +372,62 @@ static int ffm_read_data(AVFormatContext *s,
 }
 
 
+static void adjust_write_index(AVFormatContext *s)
+{
+    FFMContext *ffm = s->priv_data;
+    ByteIOContext *pb = &s->pb;
+    int64_t pts;
+    //offset_t orig_write_index = ffm->write_index;
+    offset_t pos_min, pos_max;
+    int64_t pts_start;
+    offset_t ptr = url_ftell(pb);
+
+
+    pos_min = 0;
+    pos_max = ffm->file_size - 2 * FFM_PACKET_SIZE;
+
+    pts_start = get_pts(s, pos_min);
+
+    pts = get_pts(s, pos_max);
+
+    if (pts - 100000 > pts_start) 
+        return;
+
+    ffm->write_index = FFM_PACKET_SIZE;
+
+    pts_start = get_pts(s, pos_min);
+
+    pts = get_pts(s, pos_max);
+
+    if (pts - 100000 <= pts_start) {
+        while (1) {
+            offset_t newpos;
+            int64_t newpts;
+
+            newpos = ((pos_max + pos_min) / (2 * FFM_PACKET_SIZE)) * FFM_PACKET_SIZE;
+
+            if (newpos == pos_min)
+                break;
+
+            newpts = get_pts(s, newpos);
+
+            if (newpts - 100000 <= pts) {
+                pos_max = newpos;
+                pts = newpts;
+            } else {
+                pos_min = newpos;
+            }
+        }
+        ffm->write_index += pos_max;
+    }
+
+    //printf("Adjusted write index from %lld to %lld: pts=%0.6f\n", orig_write_index, ffm->write_index, pts / 1000000.);
+    //printf("pts range %0.6f - %0.6f\n", get_pts(s, 0) / 1000000. , get_pts(s, ffm->file_size - 2 * FFM_PACKET_SIZE) / 1000000. );
+
+    url_fseek(pb, ptr, SEEK_SET);
+}
+
+
 static int ffm_read_header(AVFormatContext *s, AVFormatParameters *ap)
 {
     FFMContext *ffm = s->priv_data;
@@ -384,6 +449,7 @@ static int ffm_read_header(AVFormatContext *s, AVFormatParameters *ap)
     /* get also filesize */
     if (!url_is_streamed(pb)) {
         ffm->file_size = url_filesize(url_fileno(pb));
+        adjust_write_index(s);
     } else {
         ffm->file_size = (uint64_t_C(1) << 63) - 1;
     }