mpegts-mythtv.c: harmonize write_section_data

FFmpeg inverted its if logic, so the second MythTV hunk is now following.
That hunk may not be necessary, since the issue did not exist upstream.
It may also be incorrect for the same reason.

This doesn't break MHEG but it doesn't start as early with one of
my samples, increasing from 5 seconds in to 18 seconds in.  I'm
not sure why this changed, however.

mythtv/external/FFmpeg/libavformat/mpegts-mythtv.c

@@ -479,11 +479,9 @@ static void mpegts_push_section(MpegTSFilter *filter, const uint8_t *section, in
 static void write_section_data(MpegTSContext *ts, MpegTSFilter *tss1,
                                const uint8_t *buf, int buf_size, int is_start)
 {
-    AVFormatContext *s = ts->stream;
     MpegTSSectionFilter *tss = &tss1->u.section_filter;
-    int len;
-
-    assert(tss->section_buf);
+    uint8_t *cur_section_buf = NULL;
+    int len, offset;
 
     if (is_start) {
         memcpy(tss->section_buf, buf, buf_size);
@@ -493,29 +491,61 @@ static void write_section_data(MpegTSContext *ts, MpegTSFilter *tss1,
     } else {
         if (tss->end_of_section_reached)
             return;
-        len = 4096 - tss->section_index;
+        len = MAX_SECTION_SIZE - tss->section_index;
         if (buf_size < len)
             len = buf_size;
         memcpy(tss->section_buf + tss->section_index, buf, len);
         tss->section_index += len;
     }
 
+    // MythTV
     if (tss->section_cb == mpegts_push_section) {
         SectionContext *sect = tss->opaque;
         sect->new_packet = 1;
     }
-    while (!tss->end_of_section_reached) {
+    // end MythTV
+
+    offset = 0;
+    cur_section_buf = tss->section_buf;
+    while (cur_section_buf - tss->section_buf < MAX_SECTION_SIZE && cur_section_buf[0] != 0xff) {
         /* compute section length if possible */
-        if (tss->section_h_size == -1 && tss->section_index >= 3) {
-            len = (AV_RB16(tss->section_buf + 1) & 0xfff) + 3;
-            if (len > 4096)
+        if (tss->section_h_size == -1 && tss->section_index - offset >= 3) {
+            len = (AV_RB16(cur_section_buf + 1) & 0xfff) + 3;
+            if (len > MAX_SECTION_SIZE)
                 return;
             tss->section_h_size = len;
         }
 
-        if (tss->section_h_size == -1 ||
-            tss->section_index < tss->section_h_size)
-        {
+        if (tss->section_h_size != -1 &&
+            tss->section_index >= offset + tss->section_h_size) {
+            int crc_valid = 1;
+            tss->end_of_section_reached = 1;
+
+            if (tss->check_crc) {
+                crc_valid = !av_crc(av_crc_get_table(AV_CRC_32_IEEE), -1, cur_section_buf, tss->section_h_size);
+                if (tss->section_h_size >= 4)
+                    tss->crc = AV_RB32(cur_section_buf + tss->section_h_size - 4);
+
+                if (crc_valid) {
+                    ts->crc_validity[ tss1->pid ] = 100;
+                }else if (ts->crc_validity[ tss1->pid ] > -10) {
+                    ts->crc_validity[ tss1->pid ]--;
+                }else
+                    crc_valid = 2;
+            }
+            if (crc_valid) {
+                tss->section_cb(tss1, cur_section_buf, tss->section_h_size);
+                if (crc_valid != 1)
+                    tss->last_ver = -1;
+            }
+
+            cur_section_buf += tss->section_h_size;
+            offset += tss->section_h_size;
+            tss->section_h_size = -1;
+        } else {
+            // MythTV if; originally from: Deal with incomplete PMT streams in BBC iPlayer IPTV
+            // https://github.com/MythTV/mythtv/commit/c11ee69c81198dc221c874e8132f1f30a385fa63
+            // references https://code.mythtv.org/trac/ticket/9926 issue not in upstream!
             if (tss1->pmt_chop_at_ts && tss->section_buf[0] == PMT_TID)
             {
                 /* HACK!  To allow BBC IPTV streams with incomplete PMTs (they
@@ -526,25 +556,11 @@ static void write_section_data(MpegTSContext *ts, MpegTSFilter *tss1,
                  */
                 tss->section_h_size = tss->section_index;
             }
-            else
-                break;
-        }
-
-        if (!tss->check_crc ||
-            av_crc(av_crc_get_table(AV_CRC_32_IEEE), -1,
-                   tss->section_buf, tss->section_h_size) == 0)
-            tss->section_cb(tss1, tss->section_buf, tss->section_h_size);
-        else
-            av_log(s, AV_LOG_WARNING, "write_section_data: PID %#x CRC error\n", tss1->pid);
-
-        if (tss->section_index > tss->section_h_size) {
-            int left = tss->section_index - tss->section_h_size;
-            memmove(tss->section_buf, tss->section_buf+tss->section_h_size,
-                    left);
-            tss->section_index = left;
+            else { // upstream follows:
             tss->section_h_size = -1;
-        } else {
-            tss->end_of_section_reached = 1;
+            tss->end_of_section_reached = 0;
+            break;
+            } // end MythTV if
         }
     }
 }