[FFmpeg-devel] [PATCH] lavc/avcodec.h: extend documentation for avcodec_open2()

["zhilizhao(赵志立)"]

> On Mar 1, 2023, at 06:40, Stefano Sabatini <stefasab at gmail.com> wrote:
> 
> On date Tuesday 2023-02-28 23:28:56 +0100, Stefano Sabatini wrote:
>> In particular, clarify how to set options in the codec context, and mention when to use
>> avcodec_parameters_to_context().
>> 
>> Fix trac issue http://trac.ffmpeg.org/ticket/5781.
>> ---
>> libavcodec/avcodec.h | 29 ++++++++++++++++++++++++-----
>> 1 file changed, 24 insertions(+), 5 deletions(-)
> 

> In particular, clarify how to set options in the codec context, and mention when to use
> avcodec_parameters_to_context().
> 
> Fix trac issues:
> http://trac.ffmpeg.org/ticket/5781
> http://trac.ffmpeg.org/ticket/5838
> ---
>  libavcodec/avcodec.h | 34 +++++++++++++++++++++++++++++-----
>  1 file changed, 29 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 9a0fe97cad..fbf1d3d83c 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -2418,8 +2418,14 @@ int avcodec_parameters_to_context(AVCodecContext *codec,
>   * avcodec_find_decoder() and avcodec_find_encoder() provide an easy way for
>   * retrieving a codec.
>   *
> - * @note Always call this function before using decoding routines (such as
> - * @ref avcodec_receive_frame()).
> + * Depending on the codec, you might need to set options in the codec context
> + * also for decoding (e.g. width, height, or the pixel or audio sample format in
> + * case the information is not is not available in the bitstream, e.g. as in

'is not is not'

> + * case of decoding raw audio or video).

in ’the’ case of.

> + *
> + * Options on the codec context can be either set by providing the options
> + * specified in an AVDictionary, or by setting the values on the context itself,
> + * directly or by using the av_opt_set() API.
>   *
>   * @code
>   * av_dict_set(&opts, "b", "2.5M", 0);
> @@ -2433,17 +2439,35 @@ int avcodec_parameters_to_context(AVCodecContext *codec,
>   *     exit(1);
>   * @endcode
>   *
> + * In case AVCodecParameters are available (e.g. when demuxing a stream using
> + * libavformat, and accessing the AVStream contained in the demuxer), the codec
> + * parameters can be copied to the codec context using
> + * avcodec_parameters_to_context(), as in the following code:
> + *
> + * @code
> + * context = avcodec_alloc_context3(codec);
> + * if (avcodec_parameters_to_context(*dec_ctx, codecpar) < 0)
> + *     exit(1);
> + * if (avcodec_open2(context, codec, NULL) < 0)
> + *     exit(1);

What’s the dec_ctx?

> + * @endcode
> + *
> + * @note Always call this function before using decoding routines (such as
> + * @ref avcodec_receive_frame()).
> + *
>   * @param avctx The context to initialize.
>   * @param codec The codec to open this context for. If a non-NULL codec has been
>   *              previously passed to avcodec_alloc_context3() or
>   *              for this context, then this parameter MUST be either NULL or
>   *              equal to the previously passed codec.
> - * @param options A dictionary filled with AVCodecContext and codec-private options.
> - *                On return this object will be filled with options that were not found.
> + * @param options A dictionary filled with AVCodecContext and codec-private
> + *                options, which are set on top of the options already set in
> + *                avctx, can be NULL. On return this object will be filled with
> + *                options that were not found in avctx.
>   *
>   * @return zero on success, a negative value on error
>   * @see avcodec_alloc_context3(), avcodec_find_decoder(), avcodec_find_encoder(),
> - *      av_dict_set(), av_opt_find().
> + *      av_dict_set(), av_opt_set(), av_opt_find(), avcodec_parameters_to_context()
>   */
>  int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);
>  
> -- 
> 2.25.1