ffmpeg 使用 gdb 调试相关技巧
本文说明了,在ffmpeg二次开发或调用库的过程,如何借助于ffmpeg源码进行调试。
注:ffmpeg版本是4.0。
1. 编写代码
编写将pcm数据转换为mp2的代码
pcm_to_mp2.c
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswresample/swresample.h>
#include <stdio.h>
#include <stdbool.h>
SwrContext *g_swr_ctx = NULL;
int flush_encoder(AVFormatContext *fmt_ctx, unsigned int stream_index)
{
int ret = 0;
int got_frame = 0;
AVPacket enc_pkt;
if(!(fmt_ctx->streams[stream_index]->codec->codec->capabilities &
CODEC_CAP_DELAY))
{
return 0;
}
while(1)
{
enc_pkt.data = NULL;
enc_pkt.size = 0;
av_init_packet(&enc_pkt);
ret = avcodec_encode_audio2(fmt_ctx->streams[stream_index]->codec, &enc_pkt, NULL, &got_frame);
if(ret < 0)
{
break;
}
if(!got_frame)
{
ret = 0;
break;
}
ret = av_write_frame(fmt_ctx, &enc_pkt);
if(ret < 0)
{
break;
}
}
return ret;
}
void usage(void)
{
printf("./aac input_file output_file.mp2\n");
}
int main(int argc, char *argv[])
{
if(argc != 3)
{
usage();
return -1;
}
char *input_file = argv[1];
char *output_file = argv[2];
AVFormatContext *pFormatCtx = NULL;
AVOutputFormat *ofmt = NULL;
AVStream *audio_stream = NULL;
AVCodecContext *pCodecCtx = NULL;
AVCodec *pCodec = NULL;
uint8_t *frame_buf = NULL;
AVFrame *pFrame = NULL;
AVPacket pkt;
int got_frame = 0;
int ret = 0;
int size = 0;
int i = 0;
FILE *fp = fopen(input_file, "rb");
av_register_all();
avformat_alloc_output_context2(&pFormatCtx, NULL, NULL, output_file);
ofmt = pFormatCtx->oformat;
if(avio_open(&pFormatCtx->pb, output_file, AVIO_FLAG_READ_WRITE) < 0)
{
printf("Error: call avio_open failed!\n");
return -1;
}
audio_stream = avformat_new_stream(pFormatCtx, 0);
if(!audio_stream)
{
return -1;
}
//初始化编码器
pCodecCtx = audio_stream->codec;
pCodecCtx->codec_id = ofmt->audio_codec;
pCodecCtx->codec_type = AVMEDIA_TYPE_AUDIO;
pCodecCtx->sample_fmt = AV_SAMPLE_FMT_S16;
pCodecCtx->channel_layout = AV_CH_LAYOUT_STEREO;
pCodecCtx->channels = av_get_channel_layout_nb_channels(pCodecCtx->channel_layout);
pCodecCtx->sample_rate = 44100;
pCodecCtx->bit_rate = 192000;
pCodecCtx->frame_size = 1152;
AVFrame *src_frame = NULL;
AVFrame *dst_frame = NULL;
src_frame = av_frame_alloc();
src_frame->nb_samples = 1152;
src_frame->sample_rate = 44100;
src_frame->format= AV_SAMPLE_FMT_S16;
src_frame->channel_layout = AV_CH_LAYOUT_STEREO;
src_frame->channels = av_get_channel_layout_nb_channels(src_frame->channel_layout);
pCodec = avcodec_find_encoder(pCodecCtx->codec_id);
if(!pCodec)
{
printf("Error: call avcodec_find_encoder failed!\n");
return -1;
}
if(avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
{
printf("Error: call avcodec_open2 failed!\n");
return -1;
}
int sr_size = 0;
sr_size = av_samples_get_buffer_size(NULL, src_frame->channels, src_frame->nb_samples, src_frame->format, 1);
frame_buf = (uint8_t *)av_malloc(sr_size);
if(!frame_buf)
{
printf("Error: call av_malloc failed, sr_size = %d\n", sr_size);
return -1;
}
if(av_sample_fmt_is_planar(src_frame->format))
{
avcodec_fill_audio_frame(src_frame, src_frame->channels, src_frame->format, (const uint8_t *)frame_buf, sr_size * src_frame->channels, 1 );
}
else
{
avcodec_fill_audio_frame(src_frame, src_frame->channels, src_frame->format, (const uint8_t *)frame_buf, sr_size, 0 );
}
//Write Header
if(avformat_write_header(pFormatCtx,NULL) < 0)
{
printf("Error: call avformat_write_header..\n");
return -1;
}
AVPacket *packet = (AVPacket *)av_malloc(sizeof(AVPacket));
av_init_packet(packet);
av_dump_format(pFormatCtx, 0, output_file, 1);
src_frame->pts = 0;
while(fread(frame_buf, 1, sr_size, fp) > 0)
{
got_frame = 0;
ret = avcodec_encode_audio2(pCodecCtx, packet, src_frame, &got_frame);
if(ret < 0)
{
printf("Error: call avcodec_encode_audio2\n");
return -1;
}
i++;
src_frame->pts = i * 100;
if(1 == got_frame)
{
packet->stream_index = audio_stream->index;
ret = av_write_frame(pFormatCtx, packet);
if(ret < 0)
{
printf("Error: call av_write_frame..\n");
return -1;
}
av_free_packet(packet);
}
}
//flush encoder
ret = flush_encoder(pFormatCtx, 0);
if(ret < 0)
{
printf("Error: call flush_encoder failed!\n");
return -1;
}
if(av_write_trailer(pFormatCtx) < 0)
{
printf("Error: call av_write_trailer..\n");
return -1;
}
if(audio_stream)
{
avcodec_close(audio_stream->codec);
av_free(src_frame);
av_free(frame_buf);
}
avio_close(pFormatCtx->pb);
avformat_free_context(pFormatCtx);
av_free(packet);
fclose(fp);
printf("Encode Audio End...\n");
return 0;
}
2. 编译ffmpeg源码
$ ./configure --enable-static --disable-shared --enable-debug --disable-optimizations --disable-asm --disable-stripping --enable-doc
$ make -j 4
3. 将代码放置在examples下
将pcm_to_mp2.c
拷贝到 doc/examples目录下,该目录下都是ffmpeg的例子程序。
4. 添加编译配置
修改doc/Makefile
文件添加pcm_to_mp2
的编译项目。
修改ffbuild/config.mak
文件,
添加CONFIG_PCM_TO_MP2_EXAMPLE=yes
宏。
5. 编译
ffmpeg源码根目录下,执行make examples
这样就在doc/examples
目录下生成了pcm_to_mp2
的可执行程序。
6. gdb调试