On date Wednesday 2023-03-01 15:04:16 +0800, "zhilizhao(赵志立)" wrote: > > 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?
Updated, thanks for the feedback.
>From 672de0e5d15ab8a22f3957222680d847f60bced8 Mon Sep 17 00:00:00 2001 From: Stefano Sabatini <stefa...@gmail.com> Date: Tue, 28 Feb 2023 23:26:43 +0100 Subject: [PATCH 1/2] lavc/avcodec.h: extend documentation for avcodec_open2() 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 | 36 +++++++++++++++++++++++++++++++----- 1 file changed, 31 insertions(+), 5 deletions(-) diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h index 87ebee22b1..f630fafe24 100644 --- a/libavcodec/avcodec.h +++ b/libavcodec/avcodec.h @@ -2429,8 +2429,15 @@ 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 + * the case the information is not available in the bitstream, as when decoding + * raw audio or video). + * + * Options on the codec context can be set either by setting them in the + * provided options AVDictionary, or by setting the values on the context + * itself, directly or by using the av_opt_set() API before calling the + * function. * * @code * av_dict_set(&opts, "b", "2.5M", 0); @@ -2444,17 +2451,36 @@ 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 + * AVStream *stream = ...; + * context = avcodec_alloc_context3(codec); + * if (avcodec_parameters_to_context(context, stream->codecpar) < 0) + * exit(1); + * if (avcodec_open2(context, codec, NULL) < 0) + * exit(1); + * @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 the avctx codec context. * * @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
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