[Libav-user] Array bounds error while reading from ffmpeg data array using Purify

Navin nkipe at tatapowersed.com
Mon Dec 17 11:19:56 CET 2012

I've got a piece of code which extracts every rgb pixel from a video and 
displays it without any problem. But when I ran it with Purify, I got 
these errors:
[E] ABR: Array bounds read in GetFrame {197 occurrences}
         Reading 1 byte from 0x04ae0040 (1 byte at 0x04ae0040 illegal)
         Address 0x04ae0040 is 16 bytes before the beginning of a 
1769472 byte block at 0x04ae0050
         Address 0x04ae0040 points to a malloc'd block in heap 0x003a0000
         Thread ID: 0x17c4*

So I reduced the code to just this
*pAreaInMemory[0] = g_pFrameRGB->data[0][0];*
and I'm still getting the error (which I've shown above).
The code goes something like this (I've shown many of the 
initializations in GetFrame itself although they're supposed to be outside):

bool GetFrame()
    AVFrame*  g_pFrameRGB = NULL;
    avpicture_fill_proc((AVPicture *) g_pFrameRGB, pbuffer, 
PIX_FMT_RGB24, g_metadata->WIDTH, g_metadata->HEIGHT);
    sws_scale_proc(g_sws_ctx, (uint8_t const * const *)g_pFrame->data, 
g_pFrame->linesize, 0, g_metadata->HEIGHT, g_pFrameRGB->data, 
g_pFrameRGB->linesize );
    unsigned char* pAreaInMemory = (unsigned char*) malloc( 
sizeof(unsigned char) * 1024 * 768 );
    ...get the video data here...
    pAreaInMemory[0] = g_pFrameRGB->data[0][0];

Why is there a bounds problem when reading from data[0][0] ? I noticed 
the way data is initialized in ffmpeg. Is this purify error something I 
can ignore (there's no memory leak. Just the bounds error) or can it 
lead to serious problems?


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