Code to take into account the potential change of length field when modifying the EBML tree structure.

removeads.py

@@ -377,11 +377,30 @@ def changeEBMLElementSize(inputFile, position, addendum):
     logger.info('Found element at position: %d, size of type: %d  size of data: %d maximal size: %d.' % (initialPosition, typeSize, sizeOfData, maxSize))
     
     newSize = sizeOfData+addendum
+    delta = 0
     if  newSize > maxSize:
-        # TODO: we can reencode the header with a larger length field ...
-        logger.error('New size is too big to be encoded in actual size field.')
+        # TODO: Test this code ...
+        newEncodedSize = getEBMLLength(newSize)
+        sizeOfNewEncodedSize = len(newEncodedSize)
+        if sizeOfNewEncodedSize <= sizeOfDataSize:
+            logger.error('New encoded size is smaller (%d) or equal than previous size (%d). This should not happen.' % (sizeOfNewEncodedSize, sizeOfDataSize))
             exit(-1)
-
+        # The difference of length between old size field and new one.
+        delta = sizeOfNewEncodedSize - sizeOfDataSize
+        fileLength = fstat(infd).st_size 
+        # We seek after actual length field
+        lseek(infd, position+sizeOfDataSize, SEEK_SET)
+        # We read the rest of file
+        tail = read(infd, fileLength-(position+sizeOfDataSize))
+        # We increase file length
+        ftruncate(infd, fileLength+delta)
+        # We go to the beginning of length field
+        lseek(infd, position, SEEK_SET)
+        # We write the new length field
+        write(infd, newEncodedSize)
+        # We overwrite the rest of file with its previous content that has been offset.
+        write(infd, tail)
+    else:
         size = newSize + ((128>>(sizeOfDataSize-1))<<((sizeOfDataSize-1)*8))
         newSizeBuf = (size).to_bytes(sizeOfDataSize, byteorder='big')
 
@@ -389,8 +408,8 @@ def changeEBMLElementSize(inputFile, position, addendum):
         lseek(infd, position, SEEK_SET)
         write(infd, newSizeBuf)
     
-    # TODO: we will return the increase of length of the modified element (if its new size does not fit the older one)
-    return 0
+    # We return the potential increase in size of the file if the length field had to be increased.
+    return delta
 
 def changeCodecPrivateData(mkvinfo, inputFile, codecData):
     logger = logging.getLogger(__name__)