Hey,
Trying to fix a bug #6113, I stumbled upon some strange logic in
libavformat/img2dec.c:jpeg_probe. It accepts first 2048 bytes of jpeg stream,
and tries to read it with some state machine. If it doesn't look like jpeg
stream, it returns 0 ("it's definitely not a jpeg").
After it read through the buffer, it does this:
if (state == EOI)
return AVPROBE_SCORE_EXTENSION + 1;
if (state == SOS)
return AVPROBE_SCORE_EXTENSION / 2;
return AVPROBE_SCORE_EXTENSION / 8;
That doesn't make sense to me. All we read so far made sense for jpeg reader,
it definitely looks like a jpeg image, but for some reason our confidence is
AVPROBE_SCORE_EXTENSION _DIVIDED_ by 2 or 8 (in other words, "it would look
more jpeg if it had .jpg extension).
Compare it with png, for example:
static int png_probe(AVProbeData *p)
{
const uint8_t *b = p->buf;
if (AV_RB64(b) == 0x89504e470d0a1a0a)
return AVPROBE_SCORE_MAX - 1;
return 0;
}
"Return max confidence, if it has proper signature, 0 otherwise"
Shouldn't it be something like this?
if (state == EOI)
return AVPROBE_SCORE_EXTENSION + 3;
if (state == SOS)
return AVPROBE_SCORE_EXTENSION + 2;
return AVPROBE_SCORE_EXTENSION + 1;
I'll send a patch if there're no objections.
Thanks!
V. Kalinsky
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