Re: [FFmpeg-devel] [PATCH 4/8] fftools/ffmpeg_demux: set options on codec parameters rather than decoder

[Stefano Sabatini <stefasab@gmail.com>]

On date Friday 2024-01-05 17:42:47 +0100, Anton Khirnov wrote:
> This avoids the requirement to always have a decoder context.
> ---
>  fftools/ffmpeg_demux.c | 43 +++++++++++++++++++++---------------------
>  1 file changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/fftools/ffmpeg_demux.c b/fftools/ffmpeg_demux.c
> index cacdc76a71..892094c512 100644
> --- a/fftools/ffmpeg_demux.c
> +++ b/fftools/ffmpeg_demux.c
> @@ -899,19 +899,18 @@ static int choose_decoder(const OptionsContext *o, AVFormatContext *s, AVStream
>      }
>  }
>  
> -static int guess_input_channel_layout(InputStream *ist, int guess_layout_max)
> +static int guess_input_channel_layout(InputStream *ist, AVCodecParameters *par,
> +                                      int guess_layout_max)
>  {
> -    AVCodecContext *dec = ist->dec_ctx;
> -
> -    if (dec->ch_layout.order == AV_CHANNEL_ORDER_UNSPEC) {
> +    if (par->ch_layout.order == AV_CHANNEL_ORDER_UNSPEC) {
>          char layout_name[256];
>  
> -        if (dec->ch_layout.nb_channels > guess_layout_max)
> +        if (par->ch_layout.nb_channels > guess_layout_max)
>              return 0;
> -        av_channel_layout_default(&dec->ch_layout, dec->ch_layout.nb_channels);
> -        if (dec->ch_layout.order == AV_CHANNEL_ORDER_UNSPEC)
> +        av_channel_layout_default(&par->ch_layout, par->ch_layout.nb_channels);
> +        if (par->ch_layout.order == AV_CHANNEL_ORDER_UNSPEC)
>              return 0;
> -        av_channel_layout_describe(&dec->ch_layout, layout_name, sizeof(layout_name));
> +        av_channel_layout_describe(&par->ch_layout, layout_name, sizeof(layout_name));
>          av_log(ist, AV_LOG_WARNING, "Guessed Channel Layout: %s\n", layout_name);
>      }
>      return 1;
> @@ -1145,16 +1144,6 @@ static int ist_add(const OptionsContext *o, Demuxer *d, AVStream *st)
>          ist->user_set_discard = ist->st->discard;
>      }
>  
> -    ist->dec_ctx = avcodec_alloc_context3(ist->dec);
> -    if (!ist->dec_ctx)
> -        return AVERROR(ENOMEM);
> -
> -    ret = avcodec_parameters_to_context(ist->dec_ctx, par);
> -    if (ret < 0) {
> -        av_log(ist, AV_LOG_ERROR, "Error initializing the decoder context.\n");
> -        return ret;
> -    }
> -
>      if (o->bitexact)
>          av_dict_set(&ist->decoder_opts, "flags", "+bitexact", AV_DICT_MULTIKEY);
>  
> @@ -1181,7 +1170,7 @@ static int ist_add(const OptionsContext *o, Demuxer *d, AVStream *st)
>      case AVMEDIA_TYPE_AUDIO: {
>          int guess_layout_max = INT_MAX;
>          MATCH_PER_STREAM_OPT(guess_layout_max, i, guess_layout_max, ic, st);
> -        guess_input_channel_layout(ist, guess_layout_max);
> +        guess_input_channel_layout(ist, par, guess_layout_max);
>          break;
>      }
>      case AVMEDIA_TYPE_DATA:
> @@ -1190,7 +1179,7 @@ static int ist_add(const OptionsContext *o, Demuxer *d, AVStream *st)
>          MATCH_PER_STREAM_OPT(fix_sub_duration, i, ist->fix_sub_duration, ic, st);
>          MATCH_PER_STREAM_OPT(canvas_sizes, str, canvas_size, ic, st);
>          if (canvas_size) {
> -            ret = av_parse_video_size(&ist->dec_ctx->width, &ist->dec_ctx->height,
> +            ret = av_parse_video_size(&par->width, &par->height,
>                                        canvas_size);
>              if (ret < 0) {
>                  av_log(ist, AV_LOG_FATAL, "Invalid canvas size: %s.\n", canvas_size);
> @@ -1201,8 +1190,8 @@ static int ist_add(const OptionsContext *o, Demuxer *d, AVStream *st)
>          /* Compute the size of the canvas for the subtitles stream.
>             If the subtitles codecpar has set a size, use it. Otherwise use the
>             maximum dimensions of the video streams in the same file. */
> -        ist->sub2video.w = ist->dec_ctx->width;
> -        ist->sub2video.h = ist->dec_ctx->height;
> +        ist->sub2video.w = par->width;
> +        ist->sub2video.h = par->height;
>          if (!(ist->sub2video.w && ist->sub2video.h)) {
>              for (int j = 0; j < ic->nb_streams; j++) {
>                  AVCodecParameters *par1 = ic->streams[j]->codecpar;
> @@ -1226,6 +1215,16 @@ static int ist_add(const OptionsContext *o, Demuxer *d, AVStream *st)
>      default: av_assert0(0);
>      }
>  
> +    ist->dec_ctx = avcodec_alloc_context3(ist->dec);
> +    if (!ist->dec_ctx)
> +        return AVERROR(ENOMEM);
> +
> +    ret = avcodec_parameters_to_context(ist->dec_ctx, par);
> +    if (ret < 0) {
> +        av_log(ist, AV_LOG_ERROR, "Error initializing the decoder context.\n");
> +        return ret;
> +    }
> +

LGTM.
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