How to fix a segmentaion fault in a C program? [duplicate] - c

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Closed 11 years ago.
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Segmentation fault
Currently I am upgrading an open source program used for HTTP streaming. It needs to support the latest FFMPEG.
The code compiles fine with no warnings although I am getting a segmentation fault error.
I would like to know how to fix the issue? and / or the best way to debug? Please find attached a portion of the code due to size. I will try to add the project to github :) Thanks in advance!
Sample Usage
# segmenter --i out.ts --l 10 --o stream.m3u8 --d segments --f stream
Makefile
FFLIBS=`pkg-config --libs libavformat libavcodec libavutil`
FFFLAGS=`pkg-config --cflags libavformat libavcodec libavutil`
all:
gcc -Wall -g segmenter.c -o segmenter ${FFFLAGS} ${FFLIBS}
segmenter.c
/*
* Copyright (c) 2009 Chase Douglas
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <unistd.h>
#include "libavformat/avformat.h"
#include "libavformat/avio.h"
#include <sys/stat.h>
#include "segmenter.h"
#include "libavformat/avformat.h"
#define IMAGE_ID3_SIZE 9171
void printUsage() {
fprintf(stderr, "\nExample: segmenter --i infile --d baseDir --f baseFileName --o playListFile.m3u8 --l 10 \n");
fprintf(stderr, "\nOptions: \n");
fprintf(stderr, "--i <infile>.\n");
fprintf(stderr, "--o <outfile>.\n");
fprintf(stderr, "--d basedir, the base directory for files.\n");
fprintf(stderr, "--f baseFileName, output files will be baseFileName-#.\n");
fprintf(stderr, "--l segment length, the length of each segment.\n");
fprintf(stderr, "--a, audio only decode for < 64k streams.\n");
fprintf(stderr, "--v, video only decode for < 64k streams.\n");
fprintf(stderr, "--version, print version details and exit.\n");
fprintf(stderr, "\n\n");
}
void ffmpeg_version() {
// output build and version numbers
fprintf(stderr, " libavutil version: %s\n", AV_STRINGIFY(LIBAVUTIL_VERSION));
fprintf(stderr, " libavutil build: %d\n", LIBAVUTIL_BUILD);
fprintf(stderr, " libavcodec version: %s\n", AV_STRINGIFY(LIBAVCODEC_VERSION));
fprintf(stdout, " libavcodec build: %d\n", LIBAVCODEC_BUILD);
fprintf(stderr, " libavformat version: %s\n", AV_STRINGIFY(LIBAVFORMAT_VERSION));
fprintf(stderr, " libavformat build: %d\n", LIBAVFORMAT_BUILD);
fprintf(stderr, " built on " __DATE__ " " __TIME__);
#ifdef __GNUC__
fprintf(stderr, ", gcc: " __VERSION__ "\n");
#else
fprintf(stderr, ", using a non-gcc compiler\n");
#endif
}
static AVStream *add_output_stream(AVFormatContext *output_format_context, AVStream *input_stream) {
AVCodecContext *input_codec_context;
AVCodecContext *output_codec_context;
AVStream *output_stream;
output_stream = avformat_new_stream(output_format_context, 0);
if (!output_stream) {
fprintf(stderr, "Segmenter error: Could not allocate stream\n");
exit(1);
}
input_codec_context = input_stream->codec;
output_codec_context = output_stream->codec;
output_codec_context->codec_id = input_codec_context->codec_id;
output_codec_context->codec_type = input_codec_context->codec_type;
output_codec_context->codec_tag = input_codec_context->codec_tag;
output_codec_context->bit_rate = input_codec_context->bit_rate;
output_codec_context->extradata = input_codec_context->extradata;
output_codec_context->extradata_size = input_codec_context->extradata_size;
if (av_q2d(input_codec_context->time_base) * input_codec_context->ticks_per_frame > av_q2d(input_stream->time_base) && av_q2d(input_stream->time_base) < 1.0 / 1000) {
output_codec_context->time_base = input_codec_context->time_base;
output_codec_context->time_base.num *= input_codec_context->ticks_per_frame;
} else {
output_codec_context->time_base = input_stream->time_base;
}
switch (input_codec_context->codec_type) {
#ifdef USE_OLD_FFMPEG
case CODEC_TYPE_AUDIO:
#else
case AVMEDIA_TYPE_AUDIO:
#endif
output_codec_context->channel_layout = input_codec_context->channel_layout;
output_codec_context->sample_rate = input_codec_context->sample_rate;
output_codec_context->channels = input_codec_context->channels;
output_codec_context->frame_size = input_codec_context->frame_size;
if ((input_codec_context->block_align == 1 && input_codec_context->codec_id == CODEC_ID_MP3) || input_codec_context->codec_id == CODEC_ID_AC3) {
output_codec_context->block_align = 0;
} else {
output_codec_context->block_align = input_codec_context->block_align;
}
break;
#ifdef USE_OLD_FFMPEG
case CODEC_TYPE_VIDEO:
#else
case AVMEDIA_TYPE_VIDEO:
#endif
output_codec_context->pix_fmt = input_codec_context->pix_fmt;
output_codec_context->width = input_codec_context->width;
output_codec_context->height = input_codec_context->height;
output_codec_context->has_b_frames = input_codec_context->has_b_frames;
if (output_format_context->oformat->flags & AVFMT_GLOBALHEADER) {
output_codec_context->flags |= CODEC_FLAG_GLOBAL_HEADER;
}
break;
default:
break;
}
return output_stream;
}
int write_index_file(const char index[], const char tmp_index[], const unsigned int planned_segment_duration, const unsigned int actual_segment_duration[],
const char output_directory[], const char output_prefix[], const char output_file_extension[],
const unsigned int first_segment, const unsigned int last_segment) {
FILE *index_fp;
char *write_buf;
unsigned int i;
index_fp = fopen(tmp_index, "w");
if (!index_fp) {
fprintf(stderr, "Could not open temporary m3u8 index file (%s), no index file will be created\n", tmp_index);
return -1;
}
write_buf = malloc(sizeof (char) * 1024);
if (!write_buf) {
fprintf(stderr, "Could not allocate write buffer for index file, index file will be invalid\n");
fclose(index_fp);
return -1;
}
unsigned int maxDuration = planned_segment_duration;
for (i = first_segment; i <= last_segment; i++)
if (actual_segment_duration[i] > maxDuration)
maxDuration = actual_segment_duration[i];
snprintf(write_buf, 1024, "#EXTM3U\n#EXT-X-TARGETDURATION:%u\n", maxDuration);
if (fwrite(write_buf, strlen(write_buf), 1, index_fp) != 1) {
fprintf(stderr, "Could not write to m3u8 index file, will not continue writing to index file\n");
free(write_buf);
fclose(index_fp);
return -1;
}
for (i = first_segment; i <= last_segment; i++) {
snprintf(write_buf, 1024, "#EXTINF:%u,\n%s-%u%s\n", actual_segment_duration[i], output_prefix, i, output_file_extension);
if (fwrite(write_buf, strlen(write_buf), 1, index_fp) != 1) {
fprintf(stderr, "Could not write to m3u8 index file, will not continue writing to index file\n");
free(write_buf);
fclose(index_fp);
return -1;
}
}
snprintf(write_buf, 1024, "#EXT-X-ENDLIST\n");
if (fwrite(write_buf, strlen(write_buf), 1, index_fp) != 1) {
fprintf(stderr, "Could not write last file and endlist tag to m3u8 index file\n");
free(write_buf);
fclose(index_fp);
return -1;
}
free(write_buf);
fclose(index_fp);
return rename(tmp_index, index);
}
int main(int argc, const char *argv[]) {
//input parameters
char inputFilename[MAX_FILENAME_LENGTH], playlistFilename[MAX_FILENAME_LENGTH], baseDirName[MAX_FILENAME_LENGTH], baseFileName[MAX_FILENAME_LENGTH];
char baseFileExtension[5]; //either "ts", "aac" or "mp3"
int segmentLength, outputStreams, verbosity, version;
char currentOutputFileName[MAX_FILENAME_LENGTH];
char tempPlaylistName[MAX_FILENAME_LENGTH];
//these are used to determine the exact length of the current segment
double prev_segment_time = 0;
double segment_time;
unsigned int actual_segment_durations[2048];
double packet_time = 0;
//new variables to keep track of output size
double output_bytes = 0;
unsigned int output_index = 1;
AVOutputFormat *ofmt;
AVFormatContext *ic = NULL;
AVFormatContext *oc;
AVStream *video_st = NULL;
AVStream *audio_st = NULL;
AVCodec *codec;
int video_index;
int audio_index;
unsigned int first_segment = 1;
unsigned int last_segment = 0;
int write_index = 1;
int decode_done;
int ret;
int i;
unsigned char id3_tag[128];
unsigned char * image_id3_tag;
size_t id3_tag_size = 73;
int newFile = 1; //a boolean value to flag when a new file needs id3 tag info in it
if (parseCommandLine(inputFilename, playlistFilename, baseDirName, baseFileName, baseFileExtension, &outputStreams, &segmentLength, &verbosity, &version, argc, argv) != 0)
return 0;
if (version) {
ffmpeg_version();
return 0;
}
fprintf(stderr, "%s %s\n", playlistFilename, tempPlaylistName);
image_id3_tag = malloc(IMAGE_ID3_SIZE);
if (outputStreams == OUTPUT_STREAM_AUDIO)
build_image_id3_tag(image_id3_tag);
build_id3_tag((char *) id3_tag, id3_tag_size);
snprintf(tempPlaylistName, strlen(playlistFilename) + strlen(baseDirName) + 1, "%s%s", baseDirName, playlistFilename);
strncpy(playlistFilename, tempPlaylistName, strlen(tempPlaylistName));
strncpy(tempPlaylistName, playlistFilename, MAX_FILENAME_LENGTH);
strncat(tempPlaylistName, ".", 1);
//decide if this is an aac file or a mpegts file.
//postpone deciding format until later
/* ifmt = av_find_input_format("mpegts");
if (!ifmt)
{
fprintf(stderr, "Could not find MPEG-TS demuxer.\n");
exit(1);
} */
av_log_set_level(AV_LOG_DEBUG);
av_register_all();
ret = avformat_open_input(&ic, inputFilename, NULL, NULL);
if (ret != 0) {
fprintf(stderr, "Could not open input file %s. Error %d.\n", inputFilename, ret);
exit(1);
}
if (avformat_find_stream_info(ic, NULL) < 0) {
fprintf(stderr, "Could not read stream information.\n");
exit(1);
}
oc = avformat_alloc_context();
if (!oc) {
fprintf(stderr, "Could not allocate output context.");
exit(1);
}
video_index = -1;
audio_index = -1;
for (i = 0; i < ic->nb_streams && (video_index < 0 || audio_index < 0); i++) {
switch (ic->streams[i]->codec->codec_type) {
#ifdef USE_OLD_FFMPEG
case CODEC_TYPE_VIDEO:
#else
case AVMEDIA_TYPE_VIDEO:
#endif
video_index = i;
ic->streams[i]->discard = AVDISCARD_NONE;
if (outputStreams & OUTPUT_STREAM_VIDEO)
video_st = add_output_stream(oc, ic->streams[i]);
break;
#ifdef USE_OLD_FFMPEG
case CODEC_TYPE_AUDIO:
#else
case AVMEDIA_TYPE_AUDIO:
#endif
audio_index = i;
ic->streams[i]->discard = AVDISCARD_NONE;
if (outputStreams & OUTPUT_STREAM_AUDIO)
audio_st = add_output_stream(oc, ic->streams[i]);
break;
default:
ic->streams[i]->discard = AVDISCARD_ALL;
break;
}
}
if (video_index == -1) {
fprintf(stderr, "Stream must have video component.\n");
exit(1);
}
//now that we know the audio and video output streams
//we can decide on an output format.
if (outputStreams == OUTPUT_STREAM_AUDIO) {
//the audio output format should be the same as the audio input format
switch (ic->streams[audio_index]->codec->codec_id) {
case CODEC_ID_MP3:
fprintf(stderr, "Setting output audio to mp3.");
strncpy(baseFileExtension, ".mp3", strlen(".mp3"));
ofmt = av_guess_format("mp3", NULL, NULL);
break;
case CODEC_ID_AAC:
fprintf(stderr, "Setting output audio to aac.");
ofmt = av_guess_format("adts", NULL, NULL);
break;
default:
fprintf(stderr, "Codec id %d not supported.\n", ic->streams[audio_index]->id);
}
if (!ofmt) {
fprintf(stderr, "Could not find audio muxer.\n");
exit(1);
}
} else {
ofmt = av_guess_format("mpegts", NULL, NULL);
if (!ofmt) {
fprintf(stderr, "Could not find MPEG-TS muxer.\n");
exit(1);
}
}
oc->oformat = ofmt;
if (outputStreams & OUTPUT_STREAM_VIDEO && oc->oformat->flags & AVFMT_GLOBALHEADER) {
oc->flags |= CODEC_FLAG_GLOBAL_HEADER;
}
/* Deprecated: pass the options to avformat_write_header directly.
if (av_set_parameters(oc, NULL) < 0) {
fprintf(stderr, "Invalid output format parameters.\n");
exit(1);
}
*/
av_dump_format(oc, 0, baseFileName, 1);
//open the video codec only if there is video data
if (video_index != -1) {
if (outputStreams & OUTPUT_STREAM_VIDEO)
codec = avcodec_find_decoder(video_st->codec->codec_id);
else
codec = avcodec_find_decoder(ic->streams[video_index]->codec->codec_id);
if (!codec) {
fprintf(stderr, "Could not find video decoder, key frames will not be honored.\n");
}
if (outputStreams & OUTPUT_STREAM_VIDEO)
ret = avcodec_open2(video_st->codec, codec, NULL);
else
avcodec_open2(ic->streams[video_index]->codec, codec, NULL);
if (ret < 0) {
fprintf(stderr, "Could not open video decoder, key frames will not be honored.\n");
}
}
snprintf(currentOutputFileName, strlen(baseDirName) + strlen(baseFileName) + strlen(baseFileExtension) + 10, "%s%s-%u%s", baseDirName, baseFileName, output_index++, baseFileExtension);
if (avio_open(&oc->pb, currentOutputFileName, URL_WRONLY) < 0) {
fprintf(stderr, "Could not open '%s'.\n", currentOutputFileName);
exit(1);
}
newFile = 1;
int r = avformat_write_header(oc,NULL);
if (r) {
fprintf(stderr, "Could not write mpegts header to first output file.\n");
debugReturnCode(r);
exit(1);
}
//no segment info is written here. This just creates the shell of the playlist file
write_index = !write_index_file(playlistFilename, tempPlaylistName, segmentLength, actual_segment_durations, baseDirName, baseFileName, baseFileExtension, first_segment, last_segment);
do {
AVPacket packet;
decode_done = av_read_frame(ic, &packet);
if (decode_done < 0) {
break;
}
if (av_dup_packet(&packet) < 0) {
fprintf(stderr, "Could not duplicate packet.");
av_free_packet(&packet);
break;
}
//this time is used to check for a break in the segments
// if (packet.stream_index == video_index && (packet.flags & PKT_FLAG_KEY))
// {
// segment_time = (double)video_st->pts.val * video_st->time_base.num / video_st->time_base.den;
// }
#if USE_OLD_FFMPEG
if (packet.stream_index == video_index && (packet.flags & PKT_FLAG_KEY))
#else
if (packet.stream_index == video_index && (packet.flags & AV_PKT_FLAG_KEY))
#endif
{
segment_time = (double) packet.pts * ic->streams[video_index]->time_base.num / ic->streams[video_index]->time_base.den;
}
// else if (video_index < 0)
// {
// segment_time = (double)audio_st->pts.val * audio_st->time_base.num / audio_st->time_base.den;
// }
//get the most recent packet time
//this time is used when the time for the final segment is printed. It may not be on the edge of
//of a keyframe!
if (packet.stream_index == video_index)
packet_time = (double) packet.pts * ic->streams[video_index]->time_base.num / ic->streams[video_index]->time_base.den; //(double)video_st->pts.val * video_st->time_base.num / video_st->time_base.den;
else if (outputStreams & OUTPUT_STREAM_AUDIO)
packet_time = (double) audio_st->pts.val * audio_st->time_base.num / audio_st->time_base.den;
else
continue;
//start looking for segment splits for videos one half second before segment duration expires. This is because the
//segments are split on key frames so we cannot expect all segments to be split exactly equally.
if (segment_time - prev_segment_time >= segmentLength - 0.5) {
fprintf(stderr, "looking to print index file at time %lf\n", segment_time);
avio_flush(oc->pb);
avio_close(oc->pb);
if (write_index) {
actual_segment_durations[++last_segment] = (unsigned int) rint(segment_time - prev_segment_time);
write_index = !write_index_file(playlistFilename, tempPlaylistName, segmentLength, actual_segment_durations, baseDirName, baseFileName, baseFileExtension, first_segment, last_segment);
fprintf(stderr, "Writing index file at time %lf\n", packet_time);
}
struct stat st;
stat(currentOutputFileName, &st);
output_bytes += st.st_size;
snprintf(currentOutputFileName, strlen(baseDirName) + strlen(baseFileName) + strlen(baseFileExtension) + 10, "%s%s-%u%s", baseDirName, baseFileName, output_index++, baseFileExtension);
if (avio_open(&oc->pb, currentOutputFileName, URL_WRONLY) < 0) {
fprintf(stderr, "Could not open '%s'\n", currentOutputFileName);
break;
}
newFile = 1;
prev_segment_time = segment_time;
}
if (outputStreams == OUTPUT_STREAM_AUDIO && packet.stream_index == audio_index) {
if (newFile && outputStreams == OUTPUT_STREAM_AUDIO) {
//add id3 tag info
//fprintf(stderr, "adding id3tag to file %s\n", currentOutputFileName);
//printf("%lf %lld %lld %lld %lld %lld %lf\n", segment_time, audio_st->pts.val, audio_st->cur_dts, audio_st->cur_pkt.pts, packet.pts, packet.dts, packet.dts * av_q2d(ic->streams[audio_index]->time_base) );
fill_id3_tag((char*) id3_tag, id3_tag_size, packet.dts);
avio_write(oc->pb, id3_tag, id3_tag_size);
avio_write(oc->pb, image_id3_tag, IMAGE_ID3_SIZE);
avio_flush(oc->pb);
newFile = 0;
}
packet.stream_index = 0; //only one stream in audio only segments
ret = av_interleaved_write_frame(oc, &packet);
} else if (outputStreams & OUTPUT_STREAM_VIDEO) {
if (newFile) {
//fprintf(stderr, "New File: %lld %lld %lld\n", packet.pts, video_st->pts.val, audio_st->pts.val);
//printf("%lf %lld %lld %lld %lld %lld %lf\n", segment_time, audio_st->pts.val, audio_st->cur_dts, audio_st->cur_pkt.pts, packet.pts, packet.dts, packet.dts * av_q2d(ic->streams[audio_index]->time_base) );
newFile = 0;
}
if (outputStreams == OUTPUT_STREAM_VIDEO)
ret = av_write_frame(oc, &packet);
else
ret = av_interleaved_write_frame(oc, &packet);
}
if (ret < 0) {
fprintf(stderr, "Warning: Could not write frame of stream.\n");
} else if (ret > 0) {
fprintf(stderr, "End of stream requested.\n");
av_free_packet(&packet);
break;
}
av_free_packet(&packet);
} while (!decode_done);
//make sure all packets are written and then close the last file.
avio_flush(oc->pb);
av_write_trailer(oc);
if (video_st && video_st->codec)
avcodec_close(video_st->codec);
if (audio_st && audio_st->codec)
avcodec_close(audio_st->codec);
for (i = 0; i < oc->nb_streams; i++) {
av_freep(&oc->streams[i]->codec);
av_freep(&oc->streams[i]);
}
avio_close(oc->pb);
av_free(oc);
struct stat st;
stat(currentOutputFileName, &st);
output_bytes += st.st_size;
if (write_index) {
actual_segment_durations[++last_segment] = (unsigned int) rint(packet_time - prev_segment_time);
//make sure that the last segment length is not zero
if (actual_segment_durations[last_segment] == 0)
actual_segment_durations[last_segment] = 1;
write_index_file(playlistFilename, tempPlaylistName, segmentLength, actual_segment_durations, baseDirName, baseFileName, baseFileExtension, first_segment, last_segment);
}
write_stream_size_file(baseDirName, baseFileName, output_bytes * 8 / segment_time);
return 0;
}

Answer 1

What rudimentary debugging steps have you tried? Have you run your code under gdb or a debugger to discover what line it is crashing on? Or at the very least, added print statements to see how far into your program it is getting before the crash?
Start by compiling your source with the "-g" option in the compiler to add debugging symbols. Then run your code under gdb.
valgrind is another useful tool that might help you find where your program is crashing if it's touching invalid memory.