On Wed, Oct 30, 2024 at 4:52 PM Jose Santiago <jsanti...@haivision.com> wrote:
> +static int interlaced_frame_from_fields(AVFrame *dst,
> + const AVFrame *field1,
> + const AVFrame *field2)
> +{
> + int i, ret = 0;
> +
> + av_frame_unref(dst);
> +
> + dst->format = field1->format;
> + dst->width = field1->width;
> + dst->height = field1->height * 2;
> + dst->nb_samples = field1->nb_samples;
> + ret = av_channel_layout_copy(&dst->ch_layout, &field1->ch_layout);
> + if (ret < 0)
> + return ret;
> +
> + ret = av_frame_copy_props(dst, field1);
> + if (ret < 0)
> + return ret;
> + if (field1->duration > 0 && field1->duration != AV_NOPTS_VALUE)
> + dst->duration = field2->duration * 2;
> + else if (field2->duration > 0 && field2->duration != AV_NOPTS_VALUE)
> + dst->duration = field2->duration * 2;
> +
> + for (i = 0; i < field2->nb_side_data; i++) {
> + const AVFrameSideData *sd_src = field2->side_data[i];
> + AVFrameSideData *sd_dst;
> + AVBufferRef *ref = av_buffer_ref(sd_src->buf);
> + sd_dst = av_frame_new_side_data_from_buf(dst, sd_src->type, ref);
> + if (!sd_dst) {
> + av_buffer_unref(&ref);
> + return AVERROR(ENOMEM);
> + }
> + }
> +
> + for (i = 0; i < AV_NUM_DATA_POINTERS; i++)
> + dst->linesize[i] = field1->linesize[i]*2;
> +
> + ret = av_frame_get_buffer(dst, 0);
> + if (ret < 0)
> + return ret;
> +
> + ret = av_frame_copy(dst, field1);
> + if (ret < 0)
> + av_frame_unref(dst);
> +
> + copy_field2(dst, field2);
> +
> + for (i = 0; i < AV_NUM_DATA_POINTERS; i++)
> + dst->linesize[i] = field1->linesize[i];
> +
> + return ret;
> +}
Copying the entire frame is slow, inefficient and fundamentally
incompatible with hardware acceleration.
A correct approach would be doing what other field-based interlaced
codecs do - that is allocate a full frame picture from the start, and
decode both fields into the same frame. This then even has a chance to
work with hardware acceleration, at least in theory, at the very least
it avoids the copy overhead of the software decoder.
- Hendrik
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