[FFmpeg-devel] [PATCH] lavu: header and documentation for AVWriter

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Nicolas George
> Sent: Wednesday, August 24, 2022 5:18 PM
> To: ffmpeg-devel at ffmpeg.org
> Subject: [FFmpeg-devel] [PATCH] lavu: header and documentation for
> AVWriter
> 
> The actual implementation, tests and uses in the rest of
> FFmpeg code will be committed separately once the API is
> settled.
> 
> Signed-off-by: Nicolas George <george at nsup.org>
> ---
>  doc/avwriter_intro.md | 109 ++++++++++
>  libavutil/writer.h    | 484
> ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 593 insertions(+)
>  create mode 100644 doc/avwriter_intro.md
>  create mode 100644 libavutil/writer.h
> 
> 
> As suggested by JB, here is the header and documentation for
> AVWriter,
> to discuss the principle before investing time in polishing the
> implementation. I expect to discuss the API and if no blockign
> objections are raised push it then spend time on the implementation.
> 
> This API is a nicer and much more powerful version of BPrint. It can
> be
> used to simplify existing code where BPrint could help, plus places
> where BPrint could not help.
> 
> It also is the prerequisite for more ambitious projects, expecially
> universal serialization of FFmpeg objects (side data and such) into
> standardized formats.
> 
> The implementation is in most part done, and I am sure I can deliver.
> What remains is the boring part of integrating the tests in FATE,
> polishing various parts, updating the parts where I changed my mind
> midway, etc.
> 
> Note: FF_NEW_SZ is a macro defined elsewhere; it is really part of
> the
> implementation more than the API.
> 
> 
> diff --git a/doc/avwriter_intro.md b/doc/avwriter_intro.md
> new file mode 100644
> index 0000000000..4fd8a5a4ad
> --- /dev/null
> +++ b/doc/avwriter_intro.md
> @@ -0,0 +1,109 @@
> +# Quick start guide for AVWriter
> +
> +AVWriter is an API to unify functions returning strings (or any
> arbitrary
> +binary buffer) and to make building strings from parts easier. Here
> is a
> +quick introduction with pairs of “what I would do without AVWriter”
> /
> +“how to do it with AVWriter” of example code.
> +
> +## I want a `char*` buffer, the function wants an AVWriter
> +
> +Old-style code:
> +
> +```
> +        char *buf;
> +        ret = av_something_to_string(&buf, something);
> +        if (ret < 0)
> +            die("Failed");
> +        use_string(buf);
> +        av_freep(&buf);
> +```
> +
> +Equivalent code with AVWriter:
> +
> +```
> +        AVWriter wr = av_dynbuf_writer();
> +        av_something_write(wr, something, 0);
> +        if (av_writer_get_error(wr, 0) < 0)
> +            die("Failed");

Will it be possible to do:

av_something_write(wr, something1, 0);
av_something_write(wr, something2, 0);
av_something_write(wr, something3, 0);
if (av_writer_get_error(wr, 0) < 0)
    die("Failed");

or would av_writer_get_error() need to be called after each av_something_write()?

Thanks,
softworkz