Extracting the h264 part of a video file (demuxing) - c++

Question

I am trying to demux a video file into the video part (h264, mpeg4, h265, vp8, etc) and the audio part (mp3, aac, ac3, etc) and the subtitle part (srt) using ffmpeg in c++.
The audio part came out alright and played on all the media players I have, so also did the subtitle part. The video part however came out WITHOUT error and saved into a .h264 file but when I use ffprobe to check it or ffplay to play it, it always give the error "Invalid data found when processing input".
The code below
/* Separate a media file into audio, video and subtitle files (demuxing, complex) */
//TODO: mute error when subtitle is not present
#define __STDC_CONSTANT_MACROS
extern "C"
{
#include "libavformat/avformat.h"
}
int main()
{
//Input AVFormatContext and Output AVFormatContext
AVOutputFormat *ofmt_a = NULL, *ofmt_v = NULL, *ofmt_s = NULL;
AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx_a = NULL, *ofmt_ctx_v = NULL, *ofmt_ctx_s = NULL;
AVPacket pkt;
int ret, i;
int videoindex=-1, audioindex=-1, srtindex=-1;
int frame_index=0;
//Input file URL
const char *in_filename = "sample.mp4";
//Output file URL
const char *out_filename_v = "sample.h264";
const char *out_filename_a = "sample.mp3";
const char *out_filename_s = "sample.srt";
av_register_all();
//Input
if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
printf( "Could not open input file.");
goto end;
}
if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
printf( "Failed to retrieve input stream information");
goto end;
}
//Output
avformat_alloc_output_context2(&ofmt_ctx_v, NULL, NULL, out_filename_v);
if (!ofmt_ctx_v) {
printf( "Could not create output context\n");
ret = AVERROR_UNKNOWN;
goto end;
}
ofmt_v = ofmt_ctx_v->oformat;
avformat_alloc_output_context2(&ofmt_ctx_a, NULL, NULL, out_filename_a);
if (!ofmt_ctx_a) {
printf( "Could not create output context\n");
ret = AVERROR_UNKNOWN;
goto end;
}
ofmt_a = ofmt_ctx_a->oformat;
avformat_alloc_output_context2(&ofmt_ctx_s, NULL, NULL, out_filename_s);
if (!ofmt_ctx_a) {
printf( "Could not create output context\n");
ret = AVERROR_UNKNOWN;
goto end;
}
ofmt_s = ofmt_ctx_s->oformat;
for (i = 0; i < ifmt_ctx->nb_streams; i++) {
//Create output AVStream according to input AVStream
AVFormatContext *ofmt_ctx;
AVStream *in_stream = ifmt_ctx->streams[i];
AVStream *out_stream = NULL;
if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
videoindex=i;
out_stream=avformat_new_stream(ofmt_ctx_v, in_stream->codec->codec);
ofmt_ctx=ofmt_ctx_v;
}
else if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO){
audioindex=i;
out_stream=avformat_new_stream(ofmt_ctx_a, in_stream->codec->codec);
ofmt_ctx=ofmt_ctx_a;
}
else if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_SUBTITLE){
srtindex=i;
out_stream=avformat_new_stream(ofmt_ctx_s, in_stream->codec->codec);
ofmt_ctx=ofmt_ctx_s;
}
else{
break;
}
if (!out_stream) {
printf( "Failed allocating output stream\n");
ret = AVERROR_UNKNOWN;
goto end;
}
//Copy the settings of AVCodecContext
if (avcodec_copy_context(out_stream->codec, in_stream->codec) < 0) {
printf( "Failed to copy context from input to output stream codec context\n");
goto end;
}
out_stream->codec->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
}
//Dump Format------------------
printf("\n==============Input Video=============\n");
av_dump_format(ifmt_ctx, 0, in_filename, 0);
printf("\n==============Output Video============\n");
av_dump_format(ofmt_ctx_v, 0, out_filename_v, 1);
printf("\n==============Output Audio============\n");
av_dump_format(ofmt_ctx_a, 0, out_filename_a, 1);
/*printf("\n==============Output Subtitle============\n");
av_dump_format(ofmt_ctx_s, 0, out_filename_s, 1);*/
printf("\n======================================\n");
//Open output file
if (!(ofmt_v->flags & AVFMT_NOFILE)) {
if (avio_open(&ofmt_ctx_v->pb, out_filename_v, AVIO_FLAG_WRITE) < 0) {
printf( "Could not open output file '%s'", out_filename_v);
goto end;
}
}
if (!(ofmt_a->flags & AVFMT_NOFILE)) {
if (avio_open(&ofmt_ctx_a->pb, out_filename_a, AVIO_FLAG_WRITE) < 0) {
printf( "Could not open output file '%s'", out_filename_a);
goto end;
}
}
if (!(ofmt_a->flags & AVFMT_NOFILE)) {
if (avio_open(&ofmt_ctx_s->pb, out_filename_s, AVIO_FLAG_WRITE) < 0) {
printf( "Could not open output file '%s'", out_filename_s);
goto end;
}
}
//Write file header
if (avformat_write_header(ofmt_ctx_v, NULL) < 0) {
printf( "Error occurred when opening video output file\n");
goto end;
}
system("pause");
if (avformat_write_header(ofmt_ctx_a, NULL) < 0) {
printf( "Error occurred when opening audio output file\n");
goto end;
}
if (avformat_write_header(ofmt_ctx_s, NULL) < 0) {
printf( "Error occurred when opening audio output file\n");
goto end;
}
AVBitStreamFilterContext* h264bsfc = av_bitstream_filter_init("h264_mp4toannexb");
while (1) {
AVFormatContext *ofmt_ctx;
AVStream *in_stream, *out_stream;
//Get an AVPacket
if (av_read_frame(ifmt_ctx, &pkt) < 0)
break;
in_stream = ifmt_ctx->streams[pkt.stream_index];
if(pkt.stream_index==videoindex){
out_stream = ofmt_ctx_v->streams[0];
ofmt_ctx=ofmt_ctx_v;
printf("Write Video Packet. size:%d\tpts:%lld\n",pkt.size,pkt.pts);
av_bitstream_filter_filter(h264bsfc, in_stream->codec, NULL, &pkt.data, &pkt.size, pkt.data, pkt.size, 0);
}else if(pkt.stream_index==audioindex){
out_stream = ofmt_ctx_a->streams[0];
ofmt_ctx=ofmt_ctx_a;
printf("Write Audio Packet. size:%d\tpts:%lld\n",pkt.size,pkt.pts);
}
else if(pkt.stream_index==srtindex){
out_stream = ofmt_ctx_s->streams[0];
ofmt_ctx=ofmt_ctx_s;
printf("Write Subtitle Packet. size:%d\tpts:%lld\n",pkt.size,pkt.pts);
}
else{
continue;
}
//Convert PTS/DTS
pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
pkt.pos = -1;
pkt.stream_index=0;
//Write
if (av_interleaved_write_frame(ofmt_ctx, &pkt) < 0) {
printf( "Error muxing packet\n");
break;
}
//printf("Write %8d frames to output file\n",frame_index);
av_free_packet(&pkt);
frame_index++;
}
av_bitstream_filter_close(h264bsfc);
//Write file trailer
av_write_trailer(ofmt_ctx_a);
av_write_trailer(ofmt_ctx_v);
av_write_trailer(ofmt_ctx_s);
end:
avformat_close_input(&ifmt_ctx);
/* close output */
if (ofmt_ctx_a && !(ofmt_a->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx_a->pb);
if (ofmt_ctx_v && !(ofmt_v->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx_v->pb);
if (ofmt_ctx_s && !(ofmt_s->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx_s->pb);
avformat_free_context(ofmt_ctx_a);
avformat_free_context(ofmt_ctx_v);
avformat_free_context(ofmt_ctx_s);
system("pause");
if (ret < 0 && ret != AVERROR_EOF) {
printf( "Error occurred.\n");
return -1;
}
return 0;
}
EDIT 1
Screen shot of resultant h264 file
EDIT 2
I think the "error" has to do with FFMPEG's "Using AVStream.codec.time_base as a timebase hint to the muxer is deprecated. Set AVStream.time_base instead" error.
I revert to an older version of FFMPEG and with the same code, the resultant h264 file was ok!

Answer 1

You need to convert an H.264 bitstream from length prefixed mode to start code prefixed mode.This is required by some streaming formats, typically the MPEG-2 transport stream format ("mpegts").
Take a look at https://www.ffmpeg.org/ffmpeg-bitstream-filters.html#h264_005fmp4toannexb
Look at lines from 402 to 424 and from 842 to 843.
https://www.ffmpeg.org/doxygen/0.7/crystalhd_8c-source.html
I used it, to extract h264 from mp4.
//Use this filter on your first h264 input AVPacket
AVFormatContext *ifmt_ctx = NULL;
//...
//... //init input
//...
AVPacket *firstPacket;
//...
//... //get packet from stream
//...
uint8_t *dummy_p;
int dummy_int;
AVBitStreamFilterContext *filter = v_bitstream_filter_init("h264_mp4toannexb");
if (!filter)
{
printf("Can't open filter\n");
exit(1);
}
ret = av_bitstream_filter_filter(filter, ifmt_ctx->streams[videoindex]->codec, NULL,
&dummy_p, &dummy_int,
firstPacket->data, firstPacket->size, 0);
if( ret < 0 )
{
printf("Can't filter\n");
exit(1);
}
// use dummy_p to write to file, as first packet