[Libav-user] decoding H264 frames

[Imran Khan]

Hello All

I am trying to decode raw H264 frames using libavcodec. After getting
frames from webcam I am encoding it using H264 codec. After that I am
passing these frames one by one to a H264 decoder. In decoder
AVCodecContext I am setting width,height and  pixel format only. Problem
is decoder not decompressing the frames. the size of the frame are same as
the encoded frame size. Can anyone tell me what may be the problem.

Here is my decoder code...

#include "video_decoder.h"

using namespace std;

uint8_t* rgb_bytes;

AVFrame *alloc_dec_picture(enum PixelFormat pix_fmt, int width, int
height){
  
	AVFrame *picture;

    uint8_t *picture_buf;

    int size;
    picture = avcodec_alloc_frame();

    if (!picture)
        return NULL;

    size = avpicture_get_size(pix_fmt, width, height);

    picture_buf = (uint8_t*)av_malloc(size);

    if (!picture_buf) {

        av_free(picture);

        return NULL;

    }

    avpicture_fill((AVPicture *)picture, picture_buf,pix_fmt, width,
height);

    return picture;

}

VideoDecoder::VideoDecoder(){

	avcodec_register_all();

	avctx = NULL;

	picture = NULL;

	frame = NULL;

}


char* VideoDecoder::decoder_init(AVCodecID codec_id){

	int error;

	AVCodec* codec;

	av_init_packet(&avpkt);

	codec = avcodec_find_decoder(codec_id);
    
	if(!codec){

	return "codec not found";


	}

	avctx = avcodec_alloc_context3(codec);

	if(!avctx){

		return "can not allocate avcontext :: avocdec_alloc_context";

	}

	avctx->width=640;
	
	avctx->height=480;

	avctx->pix_fmt=AV_PIX_FMT_YUV420P;

	if(codec->capabilities&CODEC_CAP_TRUNCATED)
        avctx->flags|= CODEC_FLAG_TRUNCATED;

	error = avcodec_open2(avctx ,codec ,NULL);

	if(error < 0 ){
	
		return "can not open codec :: avcodec_open2";
	
	}

	frame = avcodec_alloc_frame();

	picture = alloc_dec_picture(PIX_FMT_RGB24, 640, 480);

	return "decoder init completed\n";
}

char* VideoDecoder::decode_frame(uint8_t *frame_buffer, size_t
data_length){

	int w = 640;

    int h = 480;

	rgb_bytes =NULL;

	int memBytes = avpicture_get_size(PIX_FMT_RGB24 , avctx->width ,
avctx->height );

	int len ,got_frame;

	avpkt.size = data_length;

	avpkt.data = frame_buffer;

	if(!frame_buffer){

	return "frame buffer empty\n";

	}

	len = avcodec_decode_video2(avctx ,frame ,&got_frame ,&avpkt);

	if( len < 0){
	
		return "error while decoding\n";
	
	}

	if( got_frame ){

	static struct SwsContext *img_convert_ctx;	

     if(img_convert_ctx == NULL) {

      img_convert_ctx = sws_getContext(w, h, 
		  PIX_FMT_YUV420P, avctx->width,
		  avctx->height, PIX_FMT_BGR24, 
		  SWS_BICUBIC, NULL, NULL, NULL);

       if(img_convert_ctx == NULL) {

	    return  "Cannot initialize the conversion context!\n";

      }

    }

	sws_scale(img_convert_ctx, 
		frame->data , frame->linesize ,
		0, h ,picture->data,
		picture->linesize );

	rgb_bytes = new uint8_t[memBytes];

	memcpy(rgb_bytes ,picture->data ,memBytes);

	}

	rgb_bytes = new uint8_t[memBytes];

	memcpy(rgb_bytes ,frame->data ,memBytes);


	av_free_packet(&avpkt);

	return "completed decoding\n";
}


-- 
Thanks and Regards
Imran Khan



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