[Libav-user] zscale: code 3074: no path between colorspaces

[Gianluca Cannata]

I have a series of JPEG files I would like to downsample and downresize
with zscale filter but It always gives me the error code in the subject of
this email.

This is the output from ffprobe:

ffprobe -v info -i /home/gianluca/Pictures/DSCF7253.JPG
ffprobe version N-116035-g6aeb084c39 Copyright (c) 2007-2024 the FFmpeg
developers
  built with gcc 11 (Ubuntu 11.4.0-1ubuntu1~22.04)
  configuration: --prefix=/usr --disable-static --enable-shared
--enable-gpl --enable-version3 --disable-programs --disable-doc
--disable-avdevice --disable-swresample --enable-swscale --disable-postproc
--disable-network --disable-everything --enable-protocol='file, subfile,
pipe' --enable-demuxer='image2, image2pipe, image_jpeg_pipe, mjpeg'
--enable-muxer=mjpeg --enable-decoder='mjpeg, mjpegb'
--enable-encoder=mjpeg --enable-parser=mjpeg --enable-filter='format, null,
copy, buffer, buffersink, scale, libplacebo, zscale' --enable-libplacebo
--enable-libzimg --enable-vulkan --enable-ffprobe --enable-ffmpeg
  libavutil      59. 26.100 / 59. 26.100
  libavcodec     61.  8.100 / 61.  8.100
  libavformat    61.  4.100 / 61.  4.100
  libavfilter    10.  2.102 / 10.  2.102
  libswscale      8.  2.100 /  8.  2.100
Input #0, image2, from '/home/gianluca/Pictures/DSCF7253.JPG':
  Duration: 00:00:00.04, start: 0.000000, bitrate: 1274307 kb/s
  Stream #0:0: Video: mjpeg (Baseline), yuvj422p(pc,
bt470bg/unknown/unknown), 4896x3264, 25 fps, 25 tbr, 25 tbn

Then I try with this code to downspample and downresize the image:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <libgen.h>

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/avfilter.h>
#include <libavfilter/buffersrc.h>
#include <libavfilter/buffersink.h>
#include <libavutil/log.h>

int main(int argc, char **argv)
{
    if (argc != 2) {
        fprintf(stderr, "usage: %s <filename>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    const char *filename = argv[1];
    const char *filename2 = basename(filename);

    av_log_set_level(AV_LOG_TRACE);

    AVFormatContext *fmt_ctx = avformat_alloc_context();
    avformat_open_input(&fmt_ctx, filename, NULL, NULL);

    AVCodecContext *dec_ctx;
    AVCodec *dec;

    av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);
    dec_ctx = avcodec_alloc_context3(dec);
    avcodec_open2(dec_ctx, dec, NULL);

    AVFrame *frame = av_frame_alloc();
    AVPacket *packet = av_packet_alloc();

    av_read_frame(fmt_ctx, packet);
    avcodec_send_packet(dec_ctx, packet);
    avcodec_receive_frame(dec_ctx, frame);
    av_packet_unref(packet);

    av_log(NULL, AV_LOG_TRACE, "filename: %s, w: %d, h: %d, fmt: %d\n",
filename, frame->width, frame->height, frame->format);

    AVFilterGraph *filter_graph = avfilter_graph_alloc();

    char buffersrc_args[512];
    snprintf(buffersrc_args, sizeof(buffersrc_args),
"video_size=%dx%d:pix_fmt=%d:time_base=1/25", frame->width, frame->height,
frame->format);
    AVFilterContext *buffersrc_ctx;
    avfilter_graph_create_filter(&buffersrc_ctx,
avfilter_get_by_name("buffer"), NULL, buffersrc_args, NULL, filter_graph);

    char zscale_args[512];
    snprintf(zscale_args, sizeof(zscale_args),
"w=%d:h=%d:f=bicubic:r=full:p=709:t=iec61966-2-1:m=470bg", (frame->width /
2), (frame->height / 2));
    AVFilterContext *zscale_ctx = NULL;
    const AVFilter *zscale_filter = avfilter_get_by_name("zscale");
    avfilter_graph_create_filter(&zscale_ctx, zscale_filter, NULL,
zscale_args, NULL, filter_graph);

    AVFilterContext *buffersink_ctx;
    avfilter_graph_create_filter(&buffersink_ctx,
avfilter_get_by_name("buffersink"), NULL, NULL, NULL, filter_graph);

    avfilter_link(buffersrc_ctx, 0, zscale_ctx, 0);
    avfilter_link(zscale_ctx, 0, buffersink_ctx, 0);

    avfilter_graph_config(filter_graph, NULL);

    AVFrame *filtered_frame = av_frame_alloc();
    av_buffersrc_add_frame(buffersrc_ctx, frame);

    while (1) {
        int ret = av_buffersink_get_frame(buffersink_ctx, filtered_frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            break;
        if (ret < 0) {
            fprintf(stderr, "av_buffersink_get_frame(): %s\n",
av_err2str(ret));
            exit(EXIT_FAILURE);
        }
    }

    av_log(NULL, AV_LOG_TRACE, "filename: %s, w: %d, h: %d, fmt: %d\n",
filename2, filtered_frame->width, filtered_frame->height,
filtered_frame->format);

    AVCodecContext *enc_ctx;
    AVCodec *enc;
    AVPacket *enc_packet = av_packet_alloc();

    enc = avcodec_find_encoder_by_name("mjpeg");
    enc_ctx = avcodec_alloc_context3(enc);
    enc_ctx->width = filtered_frame->width;
    enc_ctx->height = filtered_frame->height;
    enc_ctx->bit_rate = dec_ctx->bit_rate * 1024;
    enc_ctx->time_base = (AVRational) {1, 25};
    enc_ctx->framerate = (AVRational) {25, 1};
    enc_ctx->pix_fmt = filtered_frame->format;
    enc_ctx->strict_std_compliance = FF_COMPLIANCE_EXPERIMENTAL;
    enc_ctx->compression_level = 0;
    enc_ctx->color_range = AVCOL_RANGE_JPEG;

    avcodec_open2(enc_ctx, enc, NULL);

    avcodec_send_frame(enc_ctx, filtered_frame);
    avcodec_receive_packet(enc_ctx, enc_packet);

    FILE *dst_file = fopen(filename2, "wb");
    fwrite(enc_packet->data, 1, enc_packet->size, dst_file);
    fclose(dst_file);

    av_packet_unref(enc_packet);
    av_frame_free(&frame);
    av_frame_free(&filtered_frame);

    avfilter_graph_free(&filter_graph);

    avformat_close_input(&fmt_ctx);
    avformat_free_context(fmt_ctx);

    exit(EXIT_SUCCESS);
}

What am I doing wrong ?

Sincerely

Gianluca
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