[FFmpeg-soc] BFI Decoder

[Sisir Koppaka]

On Thu, Apr 17, 2008 at 4:19 AM, Michael Niedermayer <michaelni at gmx.at>
wrote:

> On Thu, Apr 17, 2008 at 03:51:28AM +0530, Sisir Koppaka wrote:
> > On Thu, Apr 17, 2008 at 3:45 AM, Sisir Koppaka <sisir.koppaka at gmail.com>
> > wrote:
> >
> > > 1 : back chain
> > >       if length is zero, read one more byte of the length AND two
> bytes of the offset
> > >        else, read one byte of the offset
> > >       copy (length) dwords from (output - offset) to the output
> > >
> > >       (note, that data may overlap, so don't use memmove() function
> here, just bare by-dword copying!)
> > >
> > >  case 1:                //Back Chain
> > >             if (length == 0) {
> > >                 length = bytestream_get_byte(&buf);
> > >                 offset = bytestream_get_le16(&buf);
> > >             } else {
> > >                 offset = bytestream_get_byte(&buf);
> > >             }
> > >             dst_offset = dst - offset;
> > >             length *= 4;        //Convert dwords to bytes.
> > >             while(length--)
> > >             {
> > >                 *dst++ = *dst_offset++;
> > >             }
> > >             av_log(NULL,AV_LOG_INFO, "\n[DECODER] Back Chain.");
> > >             break;
> > >
> > > Logically, it doesn't seem to be wrong to me....is it wrong?
> > >
> > > I did ./ffmpeg -i file.bfi images/%04d.png but still I only get a blue
> > > frame, I think the first frame is not decoding...it still segfaults
> while
> > > doing decoding a back chain from the av_logs...
> > >
> > This might be close to stupid or actually stupid, but I tried changing
> the
> > bytestream_get_le16 to be16 just in case, but that didn't work and gave
> the
> > same old blue.png....
> > In a further act of desperation I tried writing dst_offset = dst +
> offset;
> > because I'm not sure how the computer is actually addressing the memory
> > (does next byte necessarily have an incremented address?)(my courses
> haven't
> > got that far, if in case this is a well-known fact) this didn't work
> too...
>
> You should check/ensure that the offset and length are within the
> allocated
> buffer.
>


Now,  ./ffmpeg -i ~/Desktop/bfi/2287.bfi images/%04d.png works very well
without crashing and generates a bunch of png files.

[DECODER] Back Chain.
[DECODER] Normal Chain.
[DECODER] Back Chain.
[DECODER] Skip Chain.
[DECODER] Back Chain.frame=   57 fps=  0 q=0.0 Lsize=      -0kB time=6.3
bitrate=  -0.0kbits/s
video:997kB audio:0kB global headers:0kB muxing overhead -100.002155%
[DECODER] Finished decoding the frame.

In this line:
frame=   57 fps=  0 q=0.0 Lsize=      -0kB time=6.3 bitrate=  -0.0kbits/s

video:997kB audio:0kB global headers:0kB muxing overhead -100.002155%

Why is fps 0 and is it ok for the muxing overhead to be that much? Most
muxing overheads I saw were very small.

Some of the pictures are at http://www.flickr.com/gp/40656348@N00/44Z0J8 ,
there seems to be a problem with the decoding part.  Also weirdly, the early
frames have some halogen lighting sort of effect. The file names are the
frame numbers and there are a total of 57 frames.
-----------------
Sisir Koppaka