Re: [FFmpeg-devel] [PATCH v2 6/6] lavu/frame: deprecate AVFrame.pkt_{pos, size}

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH v2 6/6] lavu/frame: deprecate AVFrame.pkt_{pos, size}
Date: Wed, 15 Mar 2023 00:00:06 +0100
Message-ID: <20230314230006.GC375355@pb2> (raw)
In-Reply-To: <20230311105452.12933-1-anton@khirnov.net>

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On Sat, Mar 11, 2023 at 11:54:52AM +0100, Anton Khirnov wrote:
> These fields are supposed to store information about the packet the
> frame was decoded from, specifically the byte offset it was stored at
> and its size.
> 
> However,
> - the fields are highly ad-hoc - there is no strong reason why
>   specifically those (and not any other) packet properties should have a
>   dedicated field in AVFrame; unlike e.g. the timestamps, there is no
>   fundamental link between coded packet offset/size and decoded frames
> - they only make sense for frames produced by decoding demuxed packets,
>   and even then it is not always the case that the encoded data was
>   stored in the file as a contiguous sequence of bytes (in order for pos
>   to be well-defined)

> - pkt_pos was added without much explanation, apparently to allow
>   passthrough of this information through lavfi in order to handle byte
>   seeking in ffplay. That is now implemented using arbitrary user data
>   passthrough in AVFrame.opaque_ref.

One intended use i remember was that errors are detected after decoding,
be that bitstream, metadata, aspect ratio, yuv type, ...
while the location of the error is in the source file around the packets
position. pkt_pos allows one to patch errors in the source file without
remuxing

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The worst form of inequality is to try to make unequal things equal.
-- Aristotle

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