Re: [FFmpeg-devel] [PATCH v2] avcodec/pngenc: support writing iCCP chunks

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Niklas Haas:
> From: Niklas Haas <git@haasn.dev>
> 
> encode_zbuf is mostly a mirror image of decode_zbuf. Other than that,
> the code is pretty straightforward. Special care needs to be taken to
> avoid writing more than 79 characters of the profile description (the
> maximum supported).
> 
> Also add a FATE transcode test to ensure that the ICC profile gets
> encoded correctly.
> ---
> Oops. `-c copy` doesn't actually test the PNG writing code. Need to use
> `-c png` instead. Fixed in v2.
> ---
>  libavcodec/pngenc.c    | 77 +++++++++++++++++++++++++++++++++++++++++-
>  tests/fate/image.mak   |  3 ++
>  tests/ref/fate/png-icc |  8 +++++
>  3 files changed, 87 insertions(+), 1 deletion(-)
>  create mode 100644 tests/ref/fate/png-icc
> 
> diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
> index 3ebcc1e571..24530bb62f 100644
> --- a/libavcodec/pngenc.c
> +++ b/libavcodec/pngenc.c
> @@ -28,6 +28,7 @@
>  #include "apng.h"
>  
>  #include "libavutil/avassert.h"
> +#include "libavutil/bprint.h"
>  #include "libavutil/crc.h"
>  #include "libavutil/libm.h"
>  #include "libavutil/opt.h"
> @@ -343,6 +344,65 @@ static int png_get_gama(enum AVColorTransferCharacteristic trc, uint8_t *buf)
>      return 1;
>  }
>  
> +static int encode_zbuf(AVBPrint *bp, const uint8_t *data, size_t size)
> +{
> +    z_stream zstream;
> +    unsigned char *buf;
> +    unsigned buf_size;
> +    int ret;
> +
> +    zstream.zalloc = ff_png_zalloc,
> +    zstream.zfree  = ff_png_zfree,
> +    zstream.opaque = NULL;
> +    if (deflateInit(&zstream, Z_DEFAULT_COMPRESSION) != Z_OK)
> +        return AVERROR_EXTERNAL;
> +    zstream.next_in  = data;
> +    zstream.avail_in = size;
> +
> +    for (;;) {
> +        av_bprint_get_buffer(bp, 2, &buf, &buf_size);
> +        if (buf_size < 2) {
> +            deflateEnd(&zstream);
> +            return AVERROR(ENOMEM);
> +        }
> +
> +        zstream.next_out  = buf;
> +        zstream.avail_out = buf_size - 1;
> +        ret = deflate(&zstream, Z_FINISH);
> +        if (ret != Z_OK && ret != Z_STREAM_END) {
> +            deflateEnd(&zstream);
> +            return AVERROR_EXTERNAL;
> +        }
> +
> +        bp->len += zstream.next_out - buf;
> +        if (ret == Z_STREAM_END) {
> +            deflateEnd(&zstream);
> +            return 0;
> +        }
> +    }
> +}
> +
> +static int png_get_iccp(AVBPrint *bp, const AVFrameSideData *sd, char **buf_out)
> +{
> +    const AVDictionaryEntry *name;
> +    int ret;
> +
> +    av_bprint_init(bp, 0, AV_BPRINT_SIZE_UNLIMITED);
> +
> +    /* profile header */
> +    name = av_dict_get(sd->metadata, "name", NULL, 0);
> +    av_bprintf(bp, "%.79s", (name && name->value[0]) ? name->value : "icc");
> +    av_bprint_chars(bp, 0, 2); /* terminating \0 and compression method */
> +
> +    /* profile data */
> +    if ((ret = encode_zbuf(bp, sd->data, sd->size))) {
> +        av_bprint_finalize(bp, NULL);
> +        return ret;
> +    }
> +
> +    return av_bprint_finalize(bp, buf_out);

1. This is not how should work with an AVBPrint -- you are throwing the
small-string optimization away here.
2. Using an AVBPrint with its dynamic reallocations is probably not good
here at all: It is easy to get a good upper bound via deflateBound()
which allows to omit the reallocations/the loop. (I should probably have
applied
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20210317163202.672493-1-andreas.rheinhardt@gmail.com/)

> +}
> +
>  static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
>  {
>      AVFrameSideData *side_data;
> @@ -399,7 +459,22 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
>      if (png_get_gama(pict->color_trc, s->buf))
>          png_write_chunk(&s->bytestream, MKTAG('g', 'A', 'M', 'A'), s->buf, 4);
>  
> -    /* put the palette if needed */
> +    side_data = av_frame_get_side_data(pict, AV_FRAME_DATA_ICC_PROFILE);
> +    if (side_data && side_data->size) {
> +        AVBPrint bp;
> +        char *buf;
> +        int ret;
> +
> +        if ((ret = png_get_iccp(&bp, side_data, &buf))) {
> +            av_log(avctx, AV_LOG_WARNING, "Failed writing iCCP chunk: %s\n",
> +                   av_err2str(ret));

3. You should error out in case of error.

> +        } else {
> +            png_write_chunk(&s->bytestream, MKTAG('i', 'C', 'C', 'P'), buf, bp.size);
4. The size of this chunk is not accounted for in the max_packet_size.
(You are lucky that the current estimate for max_packet_size is too
generous (the zstream is not reset/flushed for each row, so it should be
deflatebound(alldata) instead of height*deflatebound(data_from_one_row)).)

> +            av_free(buf);
> +        }
> +    }
> +
> +    /* put the palette if needed, must be after colorspace information */
>      if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
>          int has_alpha, alpha, i;
>          unsigned int v;
> diff --git a/tests/fate/image.mak b/tests/fate/image.mak
> index 573d398915..da4f3709e9 100644
> --- a/tests/fate/image.mak
> +++ b/tests/fate/image.mak
> @@ -385,6 +385,9 @@ FATE_PNG_PROBE += fate-png-side-data
>  fate-png-side-data: CMD = run ffprobe$(PROGSSUF)$(EXESUF) -show_frames \
>      -i $(TARGET_SAMPLES)/png1/lena-int_rgb24.png
>  
> +FATE_PNG_PROBE += fate-png-icc
> +fate-png-icc: CMD = transcode png_pipe $(TARGET_SAMPLES)/png1/lena-int_rgb24.png image2 "-c png"
> +
>  FATE_PNG-$(call DEMDEC, IMAGE2, PNG) += $(FATE_PNG)
>  FATE_PNG_PROBE-$(call DEMDEC, IMAGE2, PNG) += $(FATE_PNG_PROBE)
>  FATE_IMAGE += $(FATE_PNG-yes)
> diff --git a/tests/ref/fate/png-icc b/tests/ref/fate/png-icc
> new file mode 100644
> index 0000000000..d3cf55263e
> --- /dev/null
> +++ b/tests/ref/fate/png-icc
> @@ -0,0 +1,8 @@
> +7e412f6a9e2c7fcb674336e5c104518d *tests/data/fate/png-icc.image2
> +49398 tests/data/fate/png-icc.image2
> +#tb 0: 1/25
> +#media_type 0: video
> +#codec_id 0: rawvideo
> +#dimensions 0: 128x128
> +#sar 0: 2835/2835
> +0,          0,          0,        1,    49152, 0xe0013dee

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