[FFmpeg-devel] [PATCH] libavcodec/mpeg12dec.c: append CC data to a53_buf_ref

[Anton Khirnov]

Quoting Scott Theisen (2024-12-14 04:06:45)
> On 12/13/24 17:39, Marth64 wrote:
> > Hi Scott,
> >
> > Thanks for sharing this. I had read your original email also
> > ([RFC] libavcodec/mpeg12dec.c: CC data from skipped frames)
> > and was thinking about the statement. The patch helps
> > visualize the issue a bit better.
> >
> > I need to study this and test it to understand it better.
> > Meantime, I will apply locally and play around with it.
> >
> > If any more seasoned EIA608 experts have any thoughts please share.
> 
> The problem is the use of av_buffer_realloc() instead of av_buffer_alloc().
> 
> | old_size |
> realloc(new_size)
> | old_size + (undefined values) | (new_size total bytes) (new_size is 
> always > old_size)
> realloc copies data already in the buffer to the first old_size bytes.
> 
> The SCTE-20 code sets the extra space to 0, but the others leave it 
> undefined.
> 
> However, the old_size data is then overwritten, potentially partially, while
> the size of the array is still new_size when there are only new_size - 
> old_size
> valid bytes.
> 
> I think it is reasonable to concatenate the CC data until a frame can be 
> exported.
> Since I don't know if there is a frame exported when all of the video 
> frame's data slices
> have been skipped (e.g. B frame with open GOP),

what exactly do you mean by 'skipped' here?

-- 
Anton Khirnov