FFMPEG: Decode video in h264rgb/libx264rgb error - c++

Question

I did a small program to encode raw images in h264rgb codec with ffmpeg.
I use this codec because I needed to encode lossless rgb images (not possible with the classic h264 codec).
But now, I have a problem. I'm not able to decode the video generated with ffmpeg. I did a second small program for that, but I get a segfault when I reach the avcodec_decode_video2() function.
I did all the initialisation correctly. I didn't forget the avcodec_register_all() and av_init_packet() functions.
Here is the code for initialisation:
_c = NULL;
_frame_nb = 0;
// Register all formats and codecs
#pragma omp critical
{
avcodec_register_all();
}
_pkt = new AVPacket;
av_init_packet(_pkt); // a defaut de pouvoir ecrire : pkt = av_packet_alloc();
if(!_pkt)
exit(1);
_codec = avcodec_find_encoder_by_name("libx264rgb");
if (!_codec) {
fprintf(stderr, "codec not found\n");
exit(1);
}
_c = avcodec_alloc_context3(_codec);
if (!_c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
_c->debug = true;
_c->pix_fmt = (AVPixelFormat)AV_PIX_FMT_RGB24;
_c->width = this->_headerCam[this->_currentCam]->iNbCol;
_c->height = this->_headerCam[this->_currentCam]->iNbLine;
_picture = av_frame_alloc();
if (!_picture) {
fprintf(stderr, "Could not allocate video _picture\n");
exit(1);
}
_tmp_picture = av_frame_alloc();
if (!_tmp_picture) {
fprintf(stderr, "Could not allocate video _tmp_picture\n");
exit(1);
}
_tmp_picture->format = (AVPixelFormat)AV_PIX_FMT_RGB24;
_tmp_picture->width = this->_headerCam[this->_currentCam]->iNbCol;
_tmp_picture->height = this->_headerCam[this->_currentCam]->iNbLine;
_tmp_picture->linesize[0] = this->_headerCam[this->_currentCam]->iNbCol;
/* open it */
if (avcodec_open2(_c, _codec, NULL) < 0) {
fprintf(stderr, "could not open codec\n");
exit(1);
}
And the decode function:
_pkt->data = NULL; // packet data will be allocated by the encoder
_pkt->size = 0;
unsigned char * inbuf;
inbuf = (uint8_t*)av_malloc(w*h*3);
//! read img size
int size_img;
fread(&size_img, sizeof(int), 1, this->_pFile);
_pkt->size = fread(inbuf, 1, size_img, this->_pFile);
_pkt->data = (unsigned char*)inbuf;
if(_pkt->size)
{
len = avcodec_decode_video2(_c, _tmp_picture, &got_picture, _pkt);
...
}
Any idea?

Answer 1

+What the comment says, instead of inbuf = (uint8_t*)av_malloc(w*h*3); you should use this:
int buffer_size = av_image_get_buffer_size((AVPixelFormat)AV_PIX_FMT_RGB24, w, h, 1);
inbuf = (uint8_t*)av_malloc(buffer_size);
Because of portability for alignment and such issues.
And also fix this line _tmp_picture->linesize[0] = ...
with this:
_tmp_picture->linesize[0] = av_image_get_linesize((AVPixelFormat)AV_PIX_FMT_RGB24, w, 0);
Hope that helps.

Answer 2

Well, I finally found a beginning of answer:
I used avcodec_find_encoder_by_name() instead of the avcodec_find_decoder_by_name()... It's certainly better if I want to decode data...
But now, I have the problem that _codec = avcodec_find_decoder_by_name("libx264rgb"); doesn't find the codec. But it works for _codec = avcodec_find_encoder_by_name("libx264rgb"); when I encoded my video.
EDIT : With _codec = avcodec_find_decoder(AV_CODEC_ID_H264); instead of _codec = avcodec_find_decoder_by_name("libx264rgb");, it is able to decode my video. It's weird but ok. Now, I hope I get lossless images.
EDIT2: Now, everything works! I got lossless decoded images with the AV_CODEC_ID_H264 decoder. To summarize, if you want to decode a video encoded with libx264rgb, you can use the classic AV_CODEC_ID_H264 codec.