FFmpeg中libswresample库简介及测试代码

快来打我* 2022-01-30 05:59 392阅读 0赞

libswresample库功能主要包括高度优化的音频重采样、rematrixing和样本格式转换操作。

以下是测试代码(test\_ffmpeg\_libswresample.cpp)，对音频了解较少，测试代码是参考examples中的：

#include "funset.hpp"
    #include <iostream>
    
    #ifdef __cplusplus
    extern "C" {
    #endif
    
    #include <libavutil/opt.h>
    #include <libavutil/channel_layout.h>
    #include <libavutil/samplefmt.h>
    #include <libswresample/swresample.h>
    
    #ifdef __cplusplus
    }
    #endif
    
    namespace {
    
    int get_format_from_sample_fmt(const char** fmt, enum AVSampleFormat sample_fmt)
    {
    	struct sample_fmt_entry {
            	enum AVSampleFormat sample_fmt; const char *fmt_be, *fmt_le;
        	} sample_fmt_entries[] = {
            	{ AV_SAMPLE_FMT_U8,  "u8",    "u8"    },
            	{ AV_SAMPLE_FMT_S16, "s16be", "s16le" },
            	{ AV_SAMPLE_FMT_S32, "s32be", "s32le" },
            	{ AV_SAMPLE_FMT_FLT, "f32be", "f32le" },
            	{ AV_SAMPLE_FMT_DBL, "f64be", "f64le" },
        	};
    
    	*fmt = nullptr;
    
        	for (int i = 0; i < FF_ARRAY_ELEMS(sample_fmt_entries); i++) {
            	struct sample_fmt_entry *entry = &sample_fmt_entries[i];
            	if (sample_fmt == entry->sample_fmt) {
                		*fmt = AV_NE(entry->fmt_be, entry->fmt_le);
                		return 0;
            	}
        	}
    
        	fprintf(stderr, "Sample format %s not supported as output format\n", av_get_sample_fmt_name(sample_fmt));
    
    	return AVERROR(EINVAL);
    }
    
    // Fill dst buffer with nb_samples, generated starting from t.
    void fill_samples(double *dst, int nb_samples, int nb_channels, int sample_rate, double *t)
    {
        	double tincr = 1.0 / sample_rate, *dstp = dst;
        	const double c = 2 * M_PI * 440.0;
    
        	// generate sin tone with 440Hz frequency and duplicated channels
        	for (int i = 0; i < nb_samples; i++) {
            	*dstp = sin(c * *t);
            	for (int j = 1; j < nb_channels; j++)
                		dstp[j] = dstp[0];
            
    		dstp += nb_channels;
            	*t += tincr;
        	}
    }
    
    } // namespace
    
    int test_ffmpeg_libswresample_resample()
    {
    	// reference: doc/examples/resample_audio.c
    
    	fprintf(stdout, "swresample version: %d\n", swresample_version());
    	fprintf(stdout, "swresample configuration: %s\n", swresample_configuration());
    	fprintf(stdout, "swresample license: %s\n", swresample_license());	
    	
    	//create resampler context
    	struct SwrContext* swr_ctx = swr_alloc();
    	if (!swr_ctx) {
    		fprintf(stderr, "fail to swr_alloc\n");
    		return -1;
    	}
    	
    	int64_t src_ch_layout = AV_CH_LAYOUT_STEREO, dst_ch_layout = AV_CH_LAYOUT_SURROUND;
    	int src_rate = 48000, dst_rate = 44100;
    	enum AVSampleFormat src_sample_fmt = AV_SAMPLE_FMT_DBL, dst_sample_fmt = AV_SAMPLE_FMT_S16;
    
    	// set options
    	av_opt_set_int(swr_ctx, "in_channel_layout",    src_ch_layout, 0);
    	av_opt_set_int(swr_ctx, "in_sample_rate",       src_rate, 0);
    	av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", src_sample_fmt, 0);
    
    	av_opt_set_int(swr_ctx, "out_channel_layout",    dst_ch_layout, 0);
    	av_opt_set_int(swr_ctx, "out_sample_rate",       dst_rate, 0);
    	av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", dst_sample_fmt, 0);
    
    	// initialize the resampling context
    	if (swr_init(swr_ctx) < 0) {
    		fprintf(stderr, "fail to swr_init\n");
    		return -1;
    	}
    	
    	uint8_t **src_data = nullptr, **dst_data = nullptr;
    	int src_nb_channels = 0, dst_nb_channels = 0;
    	int src_linesize, dst_linesize;
    	int src_nb_samples = 1024, dst_nb_samples, max_dst_nb_samples;
    	
    	// allocate source and destination samples buffers
    	src_nb_channels = av_get_channel_layout_nb_channels(src_ch_layout);
    	int ret = av_samples_alloc_array_and_samples(&src_data, &src_linesize, src_nb_channels, src_nb_samples, src_sample_fmt, 0);
    	if (ret < 0) {
    		fprintf(stderr, "fail to av_samples_alloc_array_and_samples\n");
    		return -1;
    	}
    
    	// compute the number of converted samples: buffering is avoided
    	// ensuring that the output buffer will contain at least all the converted input samples
    	max_dst_nb_samples = dst_nb_samples = av_rescale_rnd(src_nb_samples, dst_rate, src_rate, AV_ROUND_UP);
    
    	// buffer is going to be directly written to a rawaudio file, no alignment
    	dst_nb_channels = av_get_channel_layout_nb_channels(dst_ch_layout);
    	ret = av_samples_alloc_array_and_samples(&dst_data, &dst_linesize, dst_nb_channels, dst_nb_samples, dst_sample_fmt, 0);
    	if (ret < 0) {
    		fprintf(stderr, "fail to av_samples_alloc_array_and_samples\n");
    		return -1;
    	}
    
    #ifdef _MSC_VER
    	const char* file_name = "E:/GitCode/OpenCV_Test/test_images/xxx";
    #else
    	const char* file_name = "test_images/xxx";	
    #endif
    	FILE* dst_file = fopen(file_name, "wb");
    	if (!dst_file) {
    		fprintf(stderr, "fail to open file: %s\n", file_name);
    		return -1;
    	}
    
    	double t = 0;
        	do {
            	// generate synthetic audio
            	fill_samples((double *)src_data[0], src_nb_samples, src_nb_channels, src_rate, &t);
    
            	// compute destination number of samples
            	dst_nb_samples = av_rescale_rnd(swr_get_delay(swr_ctx, src_rate) + src_nb_samples, dst_rate, src_rate, AV_ROUND_UP);
            	if (dst_nb_samples > max_dst_nb_samples) {
                		av_freep(&dst_data[0]);
                		ret = av_samples_alloc(dst_data, &dst_linesize, dst_nb_channels, dst_nb_samples, dst_sample_fmt, 1);
                		if (ret < 0)
                    		break;
                		max_dst_nb_samples = dst_nb_samples;
    		}
    
            	// convert to destination format
            	ret = swr_convert(swr_ctx, dst_data, dst_nb_samples, (const uint8_t **)src_data, src_nb_samples);
            	if (ret < 0) {
                		fprintf(stderr, "fail to swr_convert\n");
                		return -1;
            	}
            	int dst_bufsize = av_samples_get_buffer_size(&dst_linesize, dst_nb_channels, ret, dst_sample_fmt, 1);
            	if (dst_bufsize < 0) {
               		fprintf(stderr, "fail to av_samples_get_buffer_size\n");
    			return -1;
            	}
            	printf("t:%f in:%d out:%d\n", t, src_nb_samples, ret);
            	fwrite(dst_data[0], 1, dst_bufsize, dst_file);
        	} while (t < 10);
    
    	const char* fmt = nullptr;
        	if ((ret = get_format_from_sample_fmt(&fmt, dst_sample_fmt)) < 0) {
            	fprintf(stderr, "fail to get_format_from_sample_fmt");
    		return -1;
    	}
    
        	fclose(dst_file);
    
        	if (src_data)
            	av_freep(&src_data[0]);
        	av_freep(&src_data);
    
        	if (dst_data)
            	av_freep(&dst_data[0]);
        	av_freep(&dst_data);
    
        	swr_free(&swr_ctx);
    
    	return 0;
    }

执行结果如下所示：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlbmdiaW5nY2h1bg_size_16_color_FFFFFF_t_70][]

**GitHub**： [https://github.com/fengbingchun/OpenCV\_Test][https_github.com_fengbingchun_OpenCV_Test]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlbmdiaW5nY2h1bg_size_16_color_FFFFFF_t_70]: /images/20220130/2534becda7ec41929ce23f6b49cf71b1.png
[https_github.com_fengbingchun_OpenCV_Test]: https://github.com/fengbingchun/OpenCV_Test