Re: [FFmpeg-devel] [PATCH 1/4] avcodec/rtv1: Check if the minimal size is available in decode_rtv1()

From: Paul B Mahol <onemda@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/4] avcodec/rtv1: Check if the minimal size is available in decode_rtv1()
Date: Sat, 23 Sep 2023 00:01:17 +0200
Message-ID: <CAPYw7P4ks5koF5XU=fwiBi6nAe6m+qvV9QUsFFs11wUcmUVLoA@mail.gmail.com> (raw)
In-Reply-To: <20230922215215.GA3543730@pb2>

On 9/22/23, Michael Niedermayer <michael@niedermayer.cc> wrote:
> On Fri, Sep 22, 2023 at 11:30:37PM +0200, Paul B Mahol wrote:
>> On 9/22/23, Michael Niedermayer <michael@niedermayer.cc> wrote:
>> > On Fri, Sep 22, 2023 at 09:32:47PM +0200, Paul B Mahol wrote:
>> >> On 9/22/23, Michael Niedermayer <michael@niedermayer.cc> wrote:
>> >> > On Thu, Jul 27, 2023 at 01:59:13AM +0200, Michael Niedermayer wrote:
>> >> >> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>> >> >> ---
>> >> >>  libavcodec/rtv1.c | 6 +++++-
>> >> >>  1 file changed, 5 insertions(+), 1 deletion(-)
>> >> >
>> >> > will apply 1-3 of this patchset
>> >>
>> >> Are you sure this does not break decoding?
>> >
>> > Well, its a loop over 4x4 blocks, a 16bit "skip" run so the minimum
>> > check looks correct.
>> > There are 2 end of bitstream checks for early exit but they look like
>> > error handling not some normal exit as they leave the frame
>> > uninitialized
>> >
>>
>> FFmpeg default initialization code for AVFrame's buffers does it
>> twice, so they are always zeroed or previous values of previous
>> buffers in pool.
>
> its rare that correct frame decoding depends on internal AVFrame buffer
> ordering
>

Users are supposed to use error checking. And I think decoder returns
error on missing frame data.

When we lost interest in preserving all decoded frame pixels as much
as possible?

>
>>
>> > Do you have some files so i can double check this is not breaking
>> > anything
>>
>> Search trac tickets.
>
> thanks, found a zip with 2 video files
> ill check it
>
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> "I am not trying to be anyone's saviour, I'm trying to think about the
>  future and not be sad" - Elon Musk
>
>
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