ffmpeg: transcoding.c проблемы

Я изучаю ffmpeg в C ++, чтобы увидеть пример ffmpeg

но я не знаю, как решить эту проблему в transcoding.c

вот моя проблема

а вот код

static int open_output_file(const char *filename)
{

AVCodecContext *dec_ctx, *enc_ctx;
AVCodec *encoder;
AVStream *in_stream, *out_stream;
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++) {

in_stream = ifmt_ctx->streams[i];
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;
}dec_ctx = in_stream->codec;
enc_ctx = out_stream->codec;printf("codec name : %s \n", avcodec_get_name(enc_ctx->codec_id));if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO || dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
/* 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;
}

/* In this example, we transcode to same properties (picture size,
* sample rate etc.). These properties can be changed for output
* streams easily using filters */
if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO) {

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 */
enc_ctx->pix_fmt = encoder->pix_fmts[0];

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

else {
enc_ctx->sample_rate = dec_ctx->sample_rate;
enc_ctx->channel_layout = dec_ctx->channel_layout;
enc_ctx->channels = av_get_channel_layout_nb_channels(enc_ctx->channel_layout);

/* take first format from list of supported formats */
enc_ctx->sample_fmt = encoder->sample_fmts[0];
enc_ctx->time_base.num = 1;
enc_ctx->time_base.den = enc_ctx->sample_rate;
}/* Third parameter can be used to pass settings to encoder */
ret = avcodec_open2(enc_ctx, encoder, NULL);

if (ret < 0) {
cout << "ret<0" << endl;
av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);
return ret;
}
}
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_copy_context(ofmt_ctx->streams[i]->codec,
ifmt_ctx->streams[i]->codec);
if (ret < 0) {
av_log(NULL, AV_LOG_ERROR, "Copying stream context failed\n");
return ret;
}
}

if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
enc_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;

}

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;

}

Я нашел эту проблему в функции open_output_file ….

но я не могу решить эту проблему ..

как я могу подойти к этой проблеме ..

Мне нужна ваша помощь,.