Re: [FFmpeg-devel] [PATCH v3 2/2] ffmpeg_opt: consider HW acceleration method when selecting decoder

[Anton Khirnov <anton@khirnov.net>]

Hi,
the concept is generally ok, but I have a few comments on the
implementation.

Quoting Xiang, Haihao (2022-07-25 06:30:51)
> +static const AVCodec *choose_decoder2(InputStream *ist, OptionsContext *o, AVFormatContext *s, AVStream *st)
> +{
> +    char *codec_name = NULL;
> +
> +    MATCH_PER_STREAM_OPT(codec_names, str, codec_name, s, st);
> +    if (codec_name) {
> +        const AVCodec *codec = find_codec_or_die(codec_name, st->codecpar->codec_type, 0);
> +        st->codecpar->codec_id = codec->id;
> +        if (recast_media && st->codecpar->codec_type != codec->type)
> +            st->codecpar->codec_type = codec->type;
> +        return codec;
> +    } else {
> +        if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
> +            ist->hwaccel_id == HWACCEL_GENERIC &&
> +            ist->hwaccel_device_type != AV_HWDEVICE_TYPE_NONE) {
> +            const AVCodec *p;

'p' is a rather weird name for an AVCodec instance, I'd expect 'c' or
'codec' or something like that

> +            void *i = 0;

NULL, it's a pointer

> +
> +            while ((p = av_codec_iterate(&i))) {
> +                int j;
> +
> +                if (p->id != st->codecpar->codec_id ||
> +                    !av_codec_is_decoder(p) ||
> +                    !avcodec_get_hw_config(p, 0))
> +                    continue;
> +
> +                for (j = 0; ;j++) {

for (int j = 0; config = avcodec_get_hw_config(p, j); j++)

gets rid of the explicit check in the loop and also
avcodec_get_hw_config() in the condition above

> +                    const AVCodecHWConfig *config = avcodec_get_hw_config(p, j);
> +
> +                    if (!config)
> +                        break;
> +
> +                    if (config->device_type == ist->hwaccel_device_type)
> +                        return p;
> +                }
> +            }
> +        }
> +
> +        return avcodec_find_decoder(st->codecpar->codec_id);
> +    }
> +}
> +
>  /* Add all the streams from the given input file to the global
>   * list of input streams. */
>  static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
> @@ -973,7 +1015,7 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
>              ist->hwaccel_pix_fmt = AV_PIX_FMT_NONE;
>          }
>  
> -        ist->dec = choose_decoder(o, ic, st);
> +        ist->dec = choose_decoder2(ist, o, ic, st);

I don't like adding a new function that partially duplicates
choose_decoder() and has a non-descriptive name. Just extend
choose_decoder() by passing hwaccel_id and hwaccel_device_type to it.


-- 
Anton Khirnov
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