[FFmpeg-devel] [PATCH 2/3] oggdec: verify page checksum

[Mattias Wadman]

On Tue, Apr 28, 2020 at 4:45 PM Lynne <dev at lynne.ee> wrote:
>
> Apr 28, 2020, 15:31 by mattias.wadman at gmail.com:
>
> > Nice, test files works fine now
> >
> > Would it make sense to conditionally ignore crc mismatch based on
> > s->error_recognition & AV_EF_CRCCHECK ?
> >
>
> I don't think so. This container specifically relies on CRC matching to identify packets
> during a seek. While other containers have more advanced sync mechanisms beyond a simple
> syncword and checksum, that's all we have here.
> What's worse, we need to be able to handle concatenated ogg files (chained opus, vorbis, etc.),
> which are widely used on internet radios. Those have the extradata needed to configure the decoder
> on the first packet. If we skip the CRC and misidentify a packet as a header, we'll misconfigure the
> decoder and break decoding until the next actual header arrives, which could be many minutes.
> The whole chained ogg mechanism is already fragile enough as it unfortunately is.

Sorry yes that make sense. I meant more that AV_EF_CRCCHECK seems to
be set by default so adding a
conditionally check would be if someone for some reason really want to
skip it using -err_detect 0 or so.

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