Re: [FFmpeg-devel] [PATCH] avfilter/src_movie: dr support

[James Almer <jamrial@gmail.com>]

> From 6fddad6ea2abf91a7378fb367a439441ef8f32b4 Mon Sep 17 00:00:00 2001
> From: Paul B Mahol <onemda@gmail.com>
> Date: Mon, 15 May 2023 21:54:25 +0200
> Subject: [PATCH 2/3] avfilter/src_movie: dr support
> 
> Signed-off-by: Paul B Mahol <onemda@gmail.com>
> ---
>  libavfilter/src_movie.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/libavfilter/src_movie.c b/libavfilter/src_movie.c
> index a7d7c188e6..0629030f91 100644
> --- a/libavfilter/src_movie.c
> +++ b/libavfilter/src_movie.c
> @@ -23,7 +23,6 @@
>   * @file
>   * movie video source
>   *
> - * @todo use direct rendering (no allocation of a new frame)
>   * @todo support a PTS correction mechanism
>   */
>  
> @@ -158,6 +157,31 @@ static AVStream *find_stream(void *log, AVFormatContext *avf, const char *spec)
>      return found;
>  }
>  
> +static int get_buffer(AVCodecContext *avctx, AVFrame *frame, int flags)
> +{
> +    AVFrame *new;
> +
> +    if (flags & AV_GET_BUFFER_FLAG_REF)
> +        return avcodec_default_get_buffer2(avctx, frame, flags);

Why? The frames returned by ff_get_{audio,video}_buffer() are refcounted 
and writable.

You should however use avcodec_default_get_buffer2() for non 
AV_CODEC_CAP_DR1 decoders. Also, you need to use 
avcodec_align_dimensions2() to get the correct dimensions.

> +
> +    switch (avctx->codec_type) {
> +    case AVMEDIA_TYPE_VIDEO:
> +        new = ff_get_video_buffer(frame->opaque, frame->width, frame->height);
> +        break;
> +    case AVMEDIA_TYPE_AUDIO:
> +        new = ff_get_audio_buffer(frame->opaque, frame->nb_samples);
> +        break;
> +    default:
> +        return -1;
> +    }
> +
> +    av_frame_unref(frame);

The documentation for get_buffer2() says:

>      * The following fields will be set in the frame before this callback is
>      * called:
>      * - format
>      * - width, height (video only)
>      * - sample_rate, channel_layout, nb_samples (audio only)
>      * Their values may differ from the corresponding values in
>      * AVCodecContext. This callback must use the frame values, not the codec
>      * context values, to calculate the required buffer size.

So you're not really supposed to touch anything else than data, buf, 
extended_data, extended_buf, and linesize, which an unref call will do. 
But as long as the necessary values in the AVFilterLink match those in 
the frame, i guess it should be ok.

> +    av_frame_move_ref(frame, new);
> +    av_frame_free(&new);
> +
> +    return 0;
> +}
> +
>  static int open_stream(AVFilterContext *ctx, MovieStream *st, int dec_threads)
>  {
>      const AVCodec *codec;
> @@ -173,6 +197,8 @@ static int open_stream(AVFilterContext *ctx, MovieStream *st, int dec_threads)
>      if (!st->codec_ctx)
>          return AVERROR(ENOMEM);
>  
> +    st->codec_ctx->flags |= AV_CODEC_FLAG_COPY_OPAQUE;
> +    st->codec_ctx->get_buffer2 = get_buffer;
>      ret = avcodec_parameters_to_context(st->codec_ctx, st->st->codecpar);
>      if (ret < 0)
>          return ret;
> @@ -480,8 +506,10 @@ static int movie_decode_packet(AVFilterContext *ctx)
>      /* send the packet to its decoder, if any */
>      pkt_out_id = pkt.stream_index > movie->max_stream_index ? -1 :
>                   movie->out_index[pkt.stream_index];
> -    if (pkt_out_id >= 0)
> +    if (pkt_out_id >= 0) {
> +        pkt.opaque = ctx->outputs[pkt_out_id];
>          ret = avcodec_send_packet(movie->st[pkt_out_id].codec_ctx, &pkt);
> +    }
>      av_packet_unref(&pkt);
>  
>      return ret;
> -- 
> 2.39.1
> 
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