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

[Lynne]

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.