FFMPEG:avfilter_graph_create_filter 初始化过滤器时方法失败

Question

我想实施托管在 FFMPEG 网站上的 transcoding.c 样本。但是 avfilter_graph_create_filter 函数失败，return 代码为 -22（第 175 行）。我只对源代码做了一个小改动，使其可以在我的 C++ 控制台应用程序中运行。我也在网上搜索过，但找不到任何有用的信息。下面是我的代码：

 extern "C" 
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/avfiltergraph.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
#include <libavutil/opt.h>
#include <libavutil/pixdesc.h>
}
static AVFormatContext *ifmt_ctx;
static AVFormatContext *ofmt_ctx;
typedef struct FilteringContext {
    AVFilterContext *buffersink_ctx;
    AVFilterContext *buffersrc_ctx;
    AVFilterGraph *filter_graph;
} FilteringContext;
static FilteringContext *filter_ctx;

static int init_filter(FilteringContext* fctx, AVCodecContext *dec_ctx,
    AVCodecContext *enc_ctx, const char *filter_spec)
{
    char args[512];
    int ret = 0;
    AVFilter *buffersrc = NULL;
    AVFilter *buffersink = NULL;
    AVFilterContext *buffersrc_ctx = NULL;
    AVFilterContext *buffersink_ctx = NULL;
    AVFilterInOut *outputs = avfilter_inout_alloc();
    AVFilterInOut *inputs = avfilter_inout_alloc();
    AVFilterGraph *filter_graph = avfilter_graph_alloc();
    if (!outputs || !inputs || !filter_graph) {
        ret = AVERROR(ENOMEM);
        goto end;
    }
    if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {
        buffersrc = avfilter_get_by_name("buffer");
        buffersink = avfilter_get_by_name("buffersink");
        if (!buffersrc || !buffersink) {
            av_log(NULL, AV_LOG_ERROR, "filtering source or sink element not found\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }
        /*sprintf(args, sizeof(args),
            "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
            dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,
            dec_ctx->time_base.num, dec_ctx->time_base.den,
            dec_ctx->sample_aspect_ratio.num,
            dec_ctx->sample_aspect_ratio.den);*/
        ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
            args, NULL, filter_graph);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");
            goto end;
        }
        ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
            NULL, NULL, filter_graph);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");
            goto end;
        }
        ret = av_opt_set_bin(buffersink_ctx, "pix_fmts",
            (uint8_t*)&enc_ctx->pix_fmt, sizeof(enc_ctx->pix_fmt),
            AV_OPT_SEARCH_CHILDREN);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");
            goto end;
        }
    }
    else if (dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
        buffersrc = avfilter_get_by_name("abuffer");
        buffersink = avfilter_get_by_name("abuffersink");
        if (!buffersrc || !buffersink) {
            av_log(NULL, AV_LOG_ERROR, "filtering source or sink element not found\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }
        if (!dec_ctx->channel_layout)
            dec_ctx->channel_layout =
            av_get_default_channel_layout(dec_ctx->channels);
        /*snprintf(args, sizeof(args),
            "time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=0x%"PRIx64,
            dec_ctx->time_base.num, dec_ctx->time_base.den, dec_ctx->sample_rate,
            av_get_sample_fmt_name(dec_ctx->sample_fmt),
            dec_ctx->channel_layout);*/
        ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
            args, NULL, filter_graph);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer source\n");
            goto end;
        }
        ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
            NULL, NULL, filter_graph);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer sink\n");
            goto end;
        }
        ret = av_opt_set_bin(buffersink_ctx, "sample_fmts",
            (uint8_t*)&enc_ctx->sample_fmt, sizeof(enc_ctx->sample_fmt),
            AV_OPT_SEARCH_CHILDREN);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot set output sample format\n");
            goto end;
        }
        ret = av_opt_set_bin(buffersink_ctx, "channel_layouts",
            (uint8_t*)&enc_ctx->channel_layout,
            sizeof(enc_ctx->channel_layout), AV_OPT_SEARCH_CHILDREN);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot set output channel layout\n");
            goto end;
        }
        ret = av_opt_set_bin(buffersink_ctx, "sample_rates",
            (uint8_t*)&enc_ctx->sample_rate, sizeof(enc_ctx->sample_rate),
            AV_OPT_SEARCH_CHILDREN);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Cannot set output sample rate\n");
            goto end;
        }
    }
    else {
        ret = AVERROR_UNKNOWN;
        goto end;
    }
    /* Endpoints for the filter graph. */
    outputs->name = av_strdup("in");
    outputs->filter_ctx = buffersrc_ctx;
    outputs->pad_idx = 0;
    outputs->next = NULL;
    inputs->name = av_strdup("out");
    inputs->filter_ctx = buffersink_ctx;
    inputs->pad_idx = 0;
    inputs->next = NULL;
    if (!outputs->name || !inputs->name) {
        ret = AVERROR(ENOMEM);
        goto end;
    }
    if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_spec,
        &inputs, &outputs, NULL)) < 0)
        goto end;
    if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
        goto end;
    /* Fill FilteringContext */
    fctx->buffersrc_ctx = buffersrc_ctx;
    fctx->buffersink_ctx = buffersink_ctx;
    fctx->filter_graph = filter_graph;
end:
    avfilter_inout_free(&inputs);
    avfilter_inout_free(&outputs);
    return ret;
}
static int init_filters(void)
{
    const char *filter_spec;
    unsigned int i;
    int ret;
    filter_ctx = (FilteringContext *)av_malloc_array(ifmt_ctx->nb_streams, sizeof(*filter_ctx));
    if (!filter_ctx)
        return AVERROR(ENOMEM);
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        filter_ctx[i].buffersrc_ctx = NULL;
        filter_ctx[i].buffersink_ctx = NULL;
        filter_ctx[i].filter_graph = NULL;
        if (!(ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
            || ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO))
            continue;
        if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
            filter_spec = "null"; /* passthrough (dummy) filter for video */
        else
            filter_spec = "anull"; /* passthrough (dummy) filter for audio */
        ret = init_filter(&filter_ctx[i], ifmt_ctx->streams[i]->codec,
            ofmt_ctx->streams[i]->codec, filter_spec);
        if (ret)
            return ret;
    }
    return 0;
}

int main(int argc, char **argv)
{
    int ret;
    AVPacket packet = {  NULL, 0 };
    AVFrame *frame = NULL;
    enum AVMediaType type;
    unsigned int stream_index;
    unsigned int i;
    int got_frame;
    int(*dec_func)(AVCodecContext *, AVFrame *, int *, const AVPacket *);

    av_register_all();
    avfilter_register_all();

    if ((ret = init_filters()) < 0)
        goto end;
    /*...*/
    system("Pause");
    return ret ? 1 : 0;
}

Answer 1

如果有一个或多个无效参数，将返回错误代码 -22 或 EINVAL。您将要创建的 buffersrc 过滤器采用额外的参数字符串 (args) 来描述传入视频的尺寸和格式。您注释掉了字符串的创建，这就是产生错误的原因。

// this should not be comment out, or replaced with way of setting the arguments
/*sprintf(args, sizeof(args),
            "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
            dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,
            dec_ctx->time_base.num, dec_ctx->time_base.den,
            dec_ctx->sample_aspect_ratio.num,
            dec_ctx->sample_aspect_ratio.den);*/
 ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in", 
                                    args, NULL, filter_graph);

如果过滤器不知道传入帧有多大以及如何解释读取值（例如，是否有 3 个 RGB 通道或 3 个 YUV 通道？它们是如何布局的，即它们是平面的还是打包的？）那应该怎么读呢？是的，它不能，它会尝试通过错误消息告诉您。

FFMPEG:avfilter_graph_create_filter 初始化过滤器时方法失败

FFMPEG:avfilter_graph_create_filter method failed when initializing filter

c

c++

ffmpeg

video-processing

transcoding