[FFmpeg-devel] [PATCH] avcodec/mjpeg: don't override color information from demuxer

[Hendrik Leppkes]

On Wed, Dec 5, 2018 at 12:35 AM Steinar H. Gunderson
<steinar+ffmpeg at gunderson.no> wrote:
>
> Some demuxers, like Matroska, allow for sending colorspace information
> that override MJPEG defaults when it comes to Y'CbCr coefficients or
> chroma location. Don't override such data if the demuxer already has
> set it; this allows decoding such MJPEG streams correctly.
>
> Also document in avcodec.h that these fields are actually set first by
> libavformat, even if libavcodec is usually the one to set them. This is
> not new behavior; e.g., dnxhd already works this way.
> ---
>  libavcodec/avcodec.h                      | 10 +++++-----
>  libavcodec/mjpegdec.c                     |  8 ++++++--
>  tests/fate/matroska.mak                   |  3 +++
>  tests/ref/fate/matroska-mjpeg-color-space | 22 ++++++++++++++++++++++
>  4 files changed, 36 insertions(+), 7 deletions(-)
>  create mode 100644 tests/ref/fate/matroska-mjpeg-color-space
>
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 3922e89331..b7ea99d8ab 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -2145,35 +2145,35 @@ typedef struct AVCodecContext {
>      /**
>       * Chromaticity coordinates of the source primaries.
>       * - encoding: Set by user
> -     * - decoding: Set by libavcodec
> +     * - decoding: Set by libavformat and/or libavcodec
>       */
>      enum AVColorPrimaries color_primaries;
>
>      /**
>       * Color Transfer Characteristic.
>       * - encoding: Set by user
> -     * - decoding: Set by libavcodec
> +     * - decoding: Set by libavformat and/or libavcodec
>       */
>      enum AVColorTransferCharacteristic color_trc;
>
>      /**
>       * YUV colorspace type.
>       * - encoding: Set by user
> -     * - decoding: Set by libavcodec
> +     * - decoding: Set by libavformat and/or libavcodec
>       */
>      enum AVColorSpace colorspace;
>
>      /**
>       * MPEG vs JPEG YUV range.
>       * - encoding: Set by user
> -     * - decoding: Set by libavcodec
> +     * - decoding: Set by libavformat and/or libavcodec
>       */
>      enum AVColorRange color_range;
>
>      /**
>       * This defines the location of chroma samples.
>       * - encoding: Set by user
> -     * - decoding: Set by libavcodec
> +     * - decoding: Set by libavformat and/or libavcodec
>       */
>      enum AVChromaLocation chroma_sample_location;
>

These comments are not accurate. avformat does not fill these values,
because outside of deprecated code it does not expose such a struct to
the user.

- Hendrik