[flac-dev] Image data in metadata modified during write?

Andy Hawkins andy at gently.org.uk
Tue Dec 6 22:12:11 UTC 2022


In article <CADQbU6-2AE_Qwo6+D9qTQS_b53w+jnxUZ8o+=UCYa=VDVPf_Mg at mail.gmail.com>,
           Martijn van Beurden<mvanb1 at gmail.com> wrote:
> As far as I know FLAC should not change image data. Could you find out
> which specific bytes differ, and whether this is consistent with
> different PNG files?

I think I got to the bottom of this. The bit of the image that's changing is
the timestamp in the header (the tIME chunk). This makes sense as when I
retrieve the image and resize it, I suspect the library that does the
resizing it writing a new timestamp in there.

Apologies for the noise, I think blaming it on the FLAC++ library was a bit
premature. Sorry!


> Op di 6 dec. 2022 om 17:42 schreef Andy Hawkins <andy at gently.org.uk>:
>> Hi,
>> I'm writing PNG data to a FLAC file using libFLAC++, and when I read it back
>> what I get seems to be different when I compare it byte for byte.  It seems
>> to be the same size, and looks the same when I compare the images visually,
>> but the actual bytes seem to be different.
>> Is there some modification done to the image when it's stored in the FLAC
>> file?
>> Thanks
>> Andy
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