c++ - 从转码示例中使用时缩放过滤器崩溃并出现错误

Question

我已经修改了一些(只是为了在 C++ 中编译)这个代码示例:
https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/transcoding.c .

什么有效:原样(空过滤器)，许多其他过滤器，如帧率，drawtext，......

什么不起作用:规模过滤器缩小时。

我使用以下语法进行缩放(我也尝试了许多其他语法，效果相同):
“比例=w=iw/2:-1”

错误是 :“输入图片宽度(240)大于步幅(128)”，其中宽度和步幅的值取决于输入。

其他环境信息:windows，VS 2017，输入示例:rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mov

关于我做错了什么的任何线索？

谢谢 !

编辑添加工作代码示例

#pragma comment(lib, "avcodec.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "avfilter.lib")

/*
* Copyright (c) 2010 Nicolas George
* Copyright (c) 2011 Stefano Sabatini
* Copyright (c) 2014 Andrey Utkin
*
**** EDITED 2017 for testing (see original here: https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/transcoding.c)
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/

/**
* @file
* API example for demuxing, decoding, filtering, encoding and muxing
* @example transcoding.c
*/

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;

typedef struct StreamContext {
    AVCodecContext *dec_ctx;
    AVCodecContext *enc_ctx;
} StreamContext;
static StreamContext *stream_ctx;

static int open_input_file(const char *filename, int& videoStreamIndex)
{
    int ret;
    unsigned int i;

    ifmt_ctx = NULL;
    if ((ret = avformat_open_input(&ifmt_ctx, filename, NULL, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
        return ret;
    }

    if ((ret = avformat_find_stream_info(ifmt_ctx, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
        return ret;
    }

    // Just need video
    videoStreamIndex = -1;
    for (unsigned int i = 0; i < ifmt_ctx->nb_streams; i++)
    {
        if (ifmt_ctx->streams[i]->codecpar->codec_type != AVMEDIA_TYPE_VIDEO)
            continue;
        videoStreamIndex = i;
        break;
    }
    if (videoStreamIndex < 0)
    {
        av_log(NULL, AV_LOG_ERROR, "Cannot find video stream\n");
        return videoStreamIndex;
    }


    stream_ctx = (StreamContext*)av_mallocz_array(ifmt_ctx->nb_streams, sizeof(*stream_ctx));
    if (!stream_ctx)
        return AVERROR(ENOMEM);

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {

        // Just need video
        if (i != videoStreamIndex)
            continue;


        AVStream *stream = ifmt_ctx->streams[i];
        AVCodec *dec = avcodec_find_decoder(stream->codecpar->codec_id);
        AVCodecContext *codec_ctx;
        if (!dec) {
            av_log(NULL, AV_LOG_ERROR, "Failed to find decoder for stream #%u\n", i);
            return AVERROR_DECODER_NOT_FOUND;
        }
        codec_ctx = avcodec_alloc_context3(dec);
        if (!codec_ctx) {
            av_log(NULL, AV_LOG_ERROR, "Failed to allocate the decoder context for stream #%u\n", i);
            return AVERROR(ENOMEM);
        }
        ret = avcodec_parameters_to_context(codec_ctx, stream->codecpar);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Failed to copy decoder parameters to input decoder context "
                "for stream #%u\n", i);
            return ret;
        }
        /* Reencode video & audio and remux subtitles etc. */
        if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO
            || codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
            if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO)
                codec_ctx->framerate = av_guess_frame_rate(ifmt_ctx, stream, NULL);
            /* Open decoder */
            ret = avcodec_open2(codec_ctx, dec, NULL);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Failed to open decoder for stream #%u\n", i);
                return ret;
            }
        }
        stream_ctx[i].dec_ctx = codec_ctx;
    }

    av_dump_format(ifmt_ctx, 0, filename, 0);
    return 0;
}

static int open_output_file(const char *filename, const int videoStreamIndex)
{
    AVStream *out_stream;
    AVStream *in_stream;
    AVCodecContext *dec_ctx, *enc_ctx;
    AVCodec *encoder;
    int ret;
    unsigned int i;

    ofmt_ctx = NULL;
    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, filename);
    if (!ofmt_ctx) {
        av_log(NULL, AV_LOG_ERROR, "Could not create output context\n");
        return AVERROR_UNKNOWN;
    }


    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        // Just need video
        if (i != videoStreamIndex)
            continue;

        out_stream = avformat_new_stream(ofmt_ctx, NULL);
        if (!out_stream) {
            av_log(NULL, AV_LOG_ERROR, "Failed allocating output stream\n");
            return AVERROR_UNKNOWN;
        }

        in_stream = ifmt_ctx->streams[i];
        dec_ctx = stream_ctx[i].dec_ctx;

        if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {
            /* in this example, we choose transcoding to same codec */
            encoder = avcodec_find_encoder(dec_ctx->codec_id);
            if (!encoder) {
                av_log(NULL, AV_LOG_FATAL, "Necessary encoder not found\n");
                return AVERROR_INVALIDDATA;
            }
            enc_ctx = avcodec_alloc_context3(encoder);
            if (!enc_ctx) {
                av_log(NULL, AV_LOG_FATAL, "Failed to allocate the encoder context\n");
                return AVERROR(ENOMEM);
            }

            /* In this example, we transcode to same properties (picture size,
            * sample rate etc.). These properties can be changed for output
            * streams easily using filters */
            enc_ctx->height = dec_ctx->height;
            enc_ctx->width = dec_ctx->width;
            enc_ctx->sample_aspect_ratio = dec_ctx->sample_aspect_ratio;
            /* take first format from list of supported formats */
            if (encoder->pix_fmts)
                enc_ctx->pix_fmt = encoder->pix_fmts[0];
            else
                enc_ctx->pix_fmt = dec_ctx->pix_fmt;

            /* video time_base can be set to whatever is handy and supported by encoder */
            //enc_ctx->time_base = av_inv_q(dec_ctx->framerate);
            enc_ctx->time_base = dec_ctx->time_base;


            /* Third parameter can be used to pass settings to encoder */
            ret = avcodec_open2(enc_ctx, encoder, NULL);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);
                return ret;
            }
            ret = avcodec_parameters_from_context(out_stream->codecpar, enc_ctx);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Failed to copy encoder parameters to output stream #%u\n", i);
                return ret;
            }
            if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
                enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

            out_stream->time_base = enc_ctx->time_base;
            stream_ctx[i].enc_ctx = enc_ctx;
        }
        else if (dec_ctx->codec_type == AVMEDIA_TYPE_UNKNOWN) {
            av_log(NULL, AV_LOG_FATAL, "Elementary stream #%d is of unknown type, cannot proceed\n", i);
            return AVERROR_INVALIDDATA;
        }
        else {
            /* if this stream must be remuxed */
            ret = avcodec_parameters_copy(out_stream->codecpar, in_stream->codecpar);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Copying parameters for stream #%u failed\n", i);
                return ret;
            }
            out_stream->time_base = in_stream->time_base;
        }

    }
    av_dump_format(ofmt_ctx, 0, filename, 1);

    if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Could not open output file '%s'", filename);
            return ret;
        }
    }

    /* init muxer, write output file header */
    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Error occurred when opening output file\n");
        return ret;
    }

    return 0;
}

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;
        }

        snprintf(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 {
        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(const int videoStreamIndex)
{
    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++) {

        // Just video
        if (i != videoStreamIndex)
            continue;

        filter_ctx[i].buffersrc_ctx = NULL;
        filter_ctx[i].buffersink_ctx = NULL;
        filter_ctx[i].filter_graph = NULL;
        if (!(ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO
            || ifmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO))
            continue;

        filter_spec = "null"; /* passthrough (dummy) filter for video */
        //filter_spec = "scale=w=iw/2:-1";
        // filter_spec = "drawtext=fontfile=FreeSerif.ttf: text='%{localtime}': x=w-text_w: y=0: fontsize=24: fontcolor=yellow@1.0: box=1: boxcolor=red@1.0";
        // filter_spec = "drawtext=fontfile=FreeSerif.ttf :text='test': x=w-text_w: y=text_h: fontsize=24: fontcolor=yellow@1.0: box=1: boxcolor=red@1.0";

        ret = init_filter(&filter_ctx[i], stream_ctx[i].dec_ctx,
            stream_ctx[i].enc_ctx, filter_spec);
        if (ret)
            return ret;
    }
    return 0;
}

static int encode_write_frame(AVFrame *filt_frame, unsigned int stream_index, int *got_frame, const int videoStreamIndex) {

    // Just video
    if (stream_index != videoStreamIndex)
        return 0;

    int ret;
    int got_frame_local;
    AVPacket enc_pkt;
    int(*enc_func)(AVCodecContext *, AVPacket *, const AVFrame *, int *) =
        (ifmt_ctx->streams[stream_index]->codecpar->codec_type ==
            AVMEDIA_TYPE_VIDEO) ? avcodec_encode_video2 : avcodec_encode_audio2;

    if (!got_frame)
        got_frame = &got_frame_local;

    // av_log(NULL, AV_LOG_INFO, "Encoding frame\n");
    /* encode filtered frame */
    enc_pkt.data = NULL;
    enc_pkt.size = 0;
    av_init_packet(&enc_pkt);

    ret = enc_func(stream_ctx[stream_index].enc_ctx, &enc_pkt,
        filt_frame, got_frame);

    av_frame_free(&filt_frame);
    if (ret < 0)
        return ret;
    if (!(*got_frame))
        return 0;

    /* prepare packet for muxing */
    /*enc_pkt.stream_index = stream_index;
    av_packet_rescale_ts(&enc_pkt, stream_ctx[stream_index].enc_ctx->time_base, ofmt_ctx->streams[stream_index]->time_base);*/
    enc_pkt.stream_index = 0;
    av_packet_rescale_ts(&enc_pkt, stream_ctx[stream_index].enc_ctx->time_base, ofmt_ctx->streams[0]->time_base);

    av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
    /* mux encoded frame */
    ret = av_interleaved_write_frame(ofmt_ctx, &enc_pkt);
    return ret;
}

static int filter_encode_write_frame(AVFrame *frame, unsigned int stream_index, const int videoStreamIndex)
{
    // Just video, all else crashes
    if (stream_index != videoStreamIndex)
        return 0;

    int ret;
    AVFrame *filt_frame;

    // av_log(NULL, AV_LOG_INFO, "Pushing decoded frame to filters\n");
    /* push the decoded frame into the filtergraph */
    ret = av_buffersrc_add_frame_flags(filter_ctx[stream_index].buffersrc_ctx,
        frame, 0);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
        return ret;
    }

    /* pull filtered frames from the filtergraph */
    while (1) {
        filt_frame = av_frame_alloc();
        if (!filt_frame) {
            ret = AVERROR(ENOMEM);
            break;
        }
        // av_log(NULL, AV_LOG_INFO, "Pulling filtered frame from filters\n");
        ret = av_buffersink_get_frame(filter_ctx[stream_index].buffersink_ctx,
            filt_frame);
        if (ret < 0) {
            /* if no more frames for output - returns AVERROR(EAGAIN)
            * if flushed and no more frames for output - returns AVERROR_EOF
            * rewrite retcode to 0 to show it as normal procedure completion
            */
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                ret = 0;
            av_frame_free(&filt_frame);
            break;
        }

        filt_frame->pict_type = AV_PICTURE_TYPE_NONE;
        ret = encode_write_frame(filt_frame, stream_index, NULL, videoStreamIndex);
        if (ret < 0)
            break;
    }

    return ret;
}

static int flush_encoder(unsigned int stream_index, const int videoStreamIndex)
{
    int ret;
    int got_frame;

    // Just video
    if (stream_index != videoStreamIndex)
        return 0;

    if (!(stream_ctx[stream_index].enc_ctx->codec->capabilities &
        AV_CODEC_CAP_DELAY))
        return 0;

    while (1) {
        av_log(NULL, AV_LOG_INFO, "Flushing stream #%u encoder\n", stream_index);
        ret = encode_write_frame(NULL, stream_index, &got_frame, videoStreamIndex);
        if (ret < 0)
            break;
        if (!got_frame)
            return 0;
    }
    return ret;
}


#include <vector>

int main(int argc, char **argv)
{
    int ret;

    AVPacket packet;
    packet.data = NULL;
    packet.size = 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 *);


#ifdef _DEBUG
    // Hardcoded arguments
    std::vector<char*> varguments;
    {
        varguments.push_back(argv[0]);

        // Source
        varguments.push_back("./big_buck_bunny_short.mp4 ");

        // Destination
        varguments.push_back("./big_buck_bunny_short-processed.mp4");
    }

    char** arguments = new char*[varguments.size()];
    for (unsigned int i = 0; i < varguments.size(); i++)
    {
        arguments[i] = varguments[i];
    }
    argc = varguments.size();
    argv = arguments;
#endif // _DEBUG


    if (argc != 3) {
        av_log(NULL, AV_LOG_ERROR, "Usage: %s <input file> <output file>\n", argv[0]);
        return 1;
    }

    av_register_all();
    avfilter_register_all();

    int videoStreamIndex = -1;
    if ((ret = open_input_file(argv[1], videoStreamIndex)) < 0)
        goto end;
    if ((ret = open_output_file(argv[2], videoStreamIndex)) < 0)
        goto end;
    if ((ret = init_filters(videoStreamIndex)) < 0)
        goto end;

    // Stop after a couple of frames
    int framesToGet = 100;

    /* read all packets */
    //while (framesToGet--)
    while(1)
    {
        if ((ret = av_read_frame(ifmt_ctx, &packet)) < 0)
            break;
        stream_index = packet.stream_index;

        // I just need video
        if (stream_index != videoStreamIndex) {
            av_packet_unref(&packet);
            continue;
        }

        type = ifmt_ctx->streams[packet.stream_index]->codecpar->codec_type;
        av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u\n",
            stream_index);

        if (filter_ctx[stream_index].filter_graph) {
            av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the frame\n");
            frame = av_frame_alloc();
            if (!frame) {
                ret = AVERROR(ENOMEM);
                break;
            }
            av_packet_rescale_ts(&packet,
                ifmt_ctx->streams[stream_index]->time_base,
                stream_ctx[stream_index].dec_ctx->time_base);
            dec_func = (type == AVMEDIA_TYPE_VIDEO) ? avcodec_decode_video2 :
                avcodec_decode_audio4;
            ret = dec_func(stream_ctx[stream_index].dec_ctx, frame,
                &got_frame, &packet);
            if (ret < 0) {
                av_frame_free(&frame);
                av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
                break;
            }

            if (got_frame) {
                frame->pts = frame->best_effort_timestamp;
                ret = filter_encode_write_frame(frame, stream_index, videoStreamIndex);
                av_frame_free(&frame);
                if (ret < 0)
                    goto end;
            }
            else {
                av_frame_free(&frame);
            }
        }
        else {
            /* remux this frame without reencoding */
            av_packet_rescale_ts(&packet,
                ifmt_ctx->streams[stream_index]->time_base,
                ofmt_ctx->streams[stream_index]->time_base);

            ret = av_interleaved_write_frame(ofmt_ctx, &packet);
            if (ret < 0)
                goto end;
        }
        av_packet_unref(&packet);
    }

    /* flush filters and encoders */
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        /* flush filter */
        if (!filter_ctx[i].filter_graph)
            continue;
        ret = filter_encode_write_frame(NULL, i, videoStreamIndex);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Flushing filter failed\n");
            goto end;
        }

        /* flush encoder */
        ret = flush_encoder(i, videoStreamIndex);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Flushing encoder failed\n");
            goto end;
        }
    }

    av_write_trailer(ofmt_ctx);
end:
    av_packet_unref(&packet);
    av_frame_free(&frame);
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        // Just video
        if (i != videoStreamIndex)
            continue;
        avcodec_free_context(&stream_ctx[i].dec_ctx);
        if (ofmt_ctx && ofmt_ctx->nb_streams > i && ofmt_ctx->streams[i] && stream_ctx[i].enc_ctx)
            avcodec_free_context(&stream_ctx[i].enc_ctx);
        if (filter_ctx && filter_ctx[i].filter_graph)
            avfilter_graph_free(&filter_ctx[i].filter_graph);
    }
    av_free(filter_ctx);
    av_free(stream_ctx);
    avformat_close_input(&ifmt_ctx);
    if (ofmt_ctx && !(ofmt_ctx->oformat->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

    /*if (ret < 0)
        av_log(NULL, AV_LOG_ERROR, "Error occurred: %s\n", av_err2str(ret));*/

    return ret ? 1 : 0;
}

Answer 1

找到了解决方案。

尽管使用完全相同的过滤器字符串调用 cmd-line ffmpeg 无需添加参数即可工作，但似乎在代码中您还需要设置编码上下文选项以防缩放。

在上面的测试代码中，它们将是:

enc_ctx->height = dec_ctx->height * scale_value;
enc_ctx->width = dec_ctx->width * scale_value;

这似乎解决了放大时的裁剪问题和缩小时的错误。

感谢大家花时间调试这个&抱歉，如果我的帖子有任何不清楚的地方(我是新手)。