On Thu, May 12, 2022 at 06:29:51PM +0200, Andreas Rheinhardt wrote:
> Andreas Rheinhardt:
> > lance.lmw...@gmail.com:
> >> On Thu, May 12, 2022 at 08:25:29AM +0200, Paul B Mahol wrote:
> >>> On Thu, May 12, 2022 at 1:39 AM <lance.lmw...@gmail.com> wrote:
> >>>
> >>>> On Wed, May 11, 2022 at 09:47:52PM +0200, Paul B Mahol wrote:
> >>>>> why?
> >>>>
> >>>> assuming the len is 1, the following code will access the next 3
> >>>> array anymore, I think it's better to check the i with len -2.
> >>>>
> >>>> for (i = 0; i < len; i += 3) {
> >>>> to
> >>>> for (i = 0; i < len - 2; i += 3) {
> >>>>
> >>>> for the return, I think it's correct to return the used length,
> >>>> if it's error, have return already. right?
> >>>
> >>>
> >>> I doubt so.
> >>
> >> maybe I'm misunderstand it, but from the comments, the API claims that:
> >> libavcodec/codec_internal.h
> >> 175 * @return amount of bytes read from the packet on success,
> >> 176 * negative error code on failure
> >> 177 */
> >> 178 int (*decode)(struct AVCodecContext *avctx, struct AVFrame
> >> *frame,
> >> 179 int *got_frame_ptr, struct AVPacket *avpkt);
> >> 180 /**
> >> 181 * Decode subtitle data to an AVSubtitle.
> >> 182 * cb is in this state if cb_type is
> >> FF_CODEC_CB_TYPE_DECODE_SUB.
> >> 183 *
> >> 184 * Apart from that this is like the decode callback.
> >> 185 */
> >> 186 int (*decode_sub)(struct AVCodecContext *avctx, struct
> >> AVSubtitle *sub,
> >> 187 int *got_frame_ptr, const struct AVPacket
> >> *avpkt);
> >>
> >
> > This is correct. It is not only the internal API which claims that, but
> > the public API, too. And this just not honoured, in particular not in
> > case of subtitle recoding. See
> > https://github.com/mkver/FFmpeg/commit/ba1564c532654888015d67b70bf73d117c2d9f75
> >
>
> It seems like there really are people who call this in a loop until all
> the input is exhausted (as the documentation leads you to believe (The
> internal uses of avcodec_decode_subtitle2 don't do this.)):
> https://github.com/HandBrake/HandBrake/blob/a40fb6bce6755209461166140f131f26a2857eb9/libhb/decavsub.c#L335
> I wonder if they ever got something meaningful the second time they
> called it with the same packet (presuming there was a second time).
At first, I thought it was an unintentional return as all other subtitle decode
return packet size always. If the code don't support for that as claims by
document,
then I prefer to fix the document. If not, we need to fix the code.
>
> - Andreas
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--
Thanks,
Limin Wang
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