private static extern void avcodec_free_context(AVCodecContext **avctx);
/**
* Open an output file and the required encoder.
* Also set some basic encoder parameters.
* Some of these parameters are based on the input file's parameters.
* @param filename File to be opened
* @param input_codec_context Codec context of input file
* @param[out] output_format_context Format context of output file
* @param[out] output_codec_context Codec context of output file
* @return Error code (0 if successful)
*/
int open_output_file(string filename, AVCodecContext *input_codec_context,
AVFormatContext **output_format_context, AVCodecContext **output_codec_context)
{
AVCodecContext *avctx = null;
AVIOContext * output_io_context = null;
AVStream * stream = null;
AVCodec * output_codec = null;
int error;
/* Open the output file to write to it. */
if ((error = avio_open(&output_io_context, filename,
AVIO_FLAG_WRITE)) < 0)
{
Console.WriteLine($"error: Could not open output file '{filename}' (error '{LibAVErrorToString(error)}')");
return(error);
}
/* Create a new format context for the output container format. */
if ((*output_format_context = avformat_alloc_context()) == null)
{
Console.WriteLine("error: Could not allocate output format context");
return(AVERROR(ENOMEM));
}
/* Associate the output file (pointer) with the container format context. */
(*output_format_context)->pb = output_io_context;
/* Guess the desired container format based on the file extension. */
if (((*output_format_context)->oformat = av_guess_format(null, filename, null)) == null)
{
Console.WriteLine("error: Could not find output file format");
goto cleanup;
}
if (((*output_format_context)->url = av_strdup(filename)) == null)
{
Console.WriteLine("error: Could not allocate url.");
error = AVERROR(ENOMEM);
goto cleanup;
}
/* Find the encoder to be used by its name. */
if ((output_codec = avcodec_find_encoder(AVCodecID.AV_CODEC_ID_VORBIS)) == null)
{
Console.WriteLine("error: Could not find a vorbis encoder.");
goto cleanup;
}
/* Create a new audio stream in the output file container. */
if ((stream = avformat_new_stream(*output_format_context, null)) == null)
{
Console.WriteLine("error: Could not create new stream");
error = AVERROR(ENOMEM);
goto cleanup;
}
avctx = avcodec_alloc_context3(output_codec);
if (avctx == null)
{
Console.WriteLine("error: Could not allocate an encoding context");
error = AVERROR(ENOMEM);
goto cleanup;
}
/* Set the basic encoder parameters.
* The input file's sample rate is used to avoid a sample rate conversion. */
/* NOTE: These parameters are tailored for vorbis.
* See https://ffmpeg.org/ffmpeg-codecs.html#libvorbis
* Other codecs may need different parameters */
avctx->channels = 2;
avctx->channel_layout = (ulong)av_get_default_channel_layout((int)avctx->channels);
avctx->sample_rate = input_codec_context->sample_rate;
avctx->sample_fmt = output_codec->sample_fmts[0];
avctx->global_quality = 7;
/* Set the sample rate for the container. */
avctx->time_base.den = input_codec_context->sample_rate;
avctx->time_base.num = 1;
/* Some container formats (like MP4) require global headers to be present.
* Mark the encoder so that it behaves accordingly. */
if (((*output_format_context)->oformat->flags & AVFMT_GLOBALHEADER) != 0)
{
avctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
}
/* Open the encoder for the audio stream to use it later. */
if ((error = avcodec_open2(avctx, output_codec, null)) < 0)
{
Console.WriteLine($"error: Could not open output codec (error '{LibAVErrorToString(error)}')");
goto cleanup;
}
error = avcodec_parameters_from_context(stream->codecpar, avctx);
if (error < 0)
{
Console.WriteLine("error: Could not initialize stream parameters");
goto cleanup;
}
/* Save the encoder context for easier access later. */
*output_codec_context = avctx;
return(0);
cleanup:
avcodec_free_context(&avctx);
avio_closep(&(*output_format_context)->pb);
avformat_free_context(*output_format_context);
*output_format_context = null;
return(error < 0 ? error : AVERROR_EXIT);
}
/**
* Open an input file and the required decoder.
* @param filename File to be opened
* @param[out] input_format_context Format context of opened file
* @param[out] input_codec_context Codec context of opened file
* @return Error code (0 if successful)
*/
int open_input_file(string filename,
AVFormatContext **input_format_context,
AVCodecContext **input_codec_context)
{
AVCodecContext *avctx;
AVCodec * input_codec;
int error;
/* Open the input file to read from it. */
if ((error = avformat_open_input(input_format_context, filename, null,
null)) < 0)
{
Console.WriteLine($"error: Could not open input file '{filename}' (error '{LibAVErrorToString(error)}')");
*input_format_context = null;
return(error);
}
/* Get information on the input file (number of streams etc.). */
if ((error = avformat_find_stream_info(*input_format_context, null)) < 0)
{
Console.WriteLine($"error: Could not open find stream info (error '{LibAVErrorToString(error)}')");
avformat_close_input(input_format_context);
return(error);
}
/* Make sure that there is only one stream in the input file. */
if ((*input_format_context)->nb_streams != 1)
{
Console.WriteLine($"error: Expected one audio input stream, but found {(*input_format_context)->nb_streams}");
avformat_close_input(input_format_context);
return(AVERROR_EXIT);
}
/* Find a decoder for the audio stream. */
if ((input_codec = avcodec_find_decoder((*input_format_context)->streams[0]->codecpar->codec_id)) == null)
{
Console.WriteLine("error: Could not find input codec");
avformat_close_input(input_format_context);
return(AVERROR_EXIT);
}
/* Allocate a new decoding context. */
avctx = avcodec_alloc_context3(input_codec);
if (avctx == null)
{
Console.WriteLine("error: Could not allocate a decoding context");
avformat_close_input(input_format_context);
return(AVERROR(ENOMEM));
}
/* Initialize the stream parameters with demuxer information. */
error = avcodec_parameters_to_context(avctx, (*input_format_context)->streams[0]->codecpar);
if (error < 0)
{
Console.WriteLine($"error: Could not avcodec_parameters_to_context (error '{LibAVErrorToString(error)}')");
avformat_close_input(input_format_context);
avcodec_free_context(&avctx);
return(error);
}
/* Open the decoder for the audio stream to use it later. */
if ((error = avcodec_open2(avctx, input_codec, null)) < 0)
{
Console.WriteLine($"error: Could not open input codec (error '{LibAVErrorToString(error)}')");
avcodec_free_context(&avctx);
avformat_close_input(input_format_context);
return(error);
}
/* Save the decoder context for easier access later. */
*input_codec_context = avctx;
return(0);
}
public static extern void avcodec_free_context(AVCodecContext **avctx);