[Libav-user] decoding video frames

[Bob Self]

I'm trying to decode video frames. The decoding loop prints this message:
      [mpeg4 @ 00823420] Invalid and inefficient vfw-avi packed B
frames detected

After that it prints these lines over and over:

      [mpeg4 @ ...] slice end not reached but screenspace end (5 left
78000, score= -2)
      [mpeg4 @ ...] concealing 1350 DC, 1350 AC, 1350 MV errors


What causes these warning messages? Is this the correct way to decode video?

thanks,
Bob


AVCodec *codec;
AVCodecContext *codec_ctx= NULL;
AVFormatContext *format_ctx=NULL;
AVFrame *picture=NULL;
int frame, got_picture, len;
FILE *f;
uint8_t inbuf[INBUF_SIZE + FF_INPUT_BUFFER_PADDING_SIZE];
char buf[1024];
AVPacket avpkt;
const char *outfilename = "x.x";
const char *filename = MOVIE;
unsigned long frames=0L;
int status;
int64_t duration = 0;
const char *cptr=NULL;
unsigned long count=0L;
unsigned long total_bytes = 0L;
int vidstream = -1;
int i;
int flags=0;

if (!exists(MOVIE))  {
   printf("can't find %s\n", MOVIE);
   exit 1;
}

av_log_set_flags(AV_LOG_SKIP_REPEATED);
avcodec_register_all();
av_register_all();
avformat_network_init();

unsigned int codec_version = avcodec_version();
av_init_packet(&avpkt);

// avcodec version: 54.10.100
printf("avcodec version = %d.%d.%d\n", (codec_version&0x00ff0000)>>16,
(codec_version&0x0000ff00)>>8, codec_version&0x000000ff);      //
version 52.72.2


format_ctx = avformat_alloc_context();
cptr = MOVIE;
status = avformat_open_input(&format_ctx, MOVIE, NULL, NULL);

if (status != 0)  {
   printf("error1\n");
   goto done;
}

// find the first video stream

for (i=0; i<(int)format_ctx->nb_streams; i++) {
   if (format_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
      vidstream = i;
      break;
   }
}

if (vidstream == -1) {
   printf("error3\n");
   goto done;
}

// Get a pointer to the codec context for the video stream
codec_ctx = format_ctx->streams[vidstream]->codec;
frames = (unsigned long)format_ctx->streams[vidstream]->nb_frames; // 154959


double d;

d = frames / 23.97; // d = 5170
d /= 3600.0; // d = 1.79 hours

memset(inbuf + INBUF_SIZE, 0, FF_INPUT_BUFFER_PADDING_SIZE);

codec = avcodec_find_decoder(CODEC_ID_MPEG4);
if (!codec) {
   fprintf(stderr, "codec not found\n");
   goto done;
}

codec_ctx = avcodec_alloc_context3(codec);
picture= avcodec_alloc_frame();

if(codec->capabilities&CODEC_CAP_TRUNCATED)  {
   codec_ctx->flags|= CODEC_FLAG_TRUNCATED;               // we do not
send complete frames
}

if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
   fprintf(stderr, "could not open codec\n");
   goto done;
}

f = fopen(filename, "rb");
if (!f) {
   fprintf(stderr, "could not open %s\n", filename);
   goto done;
}

frame = 0;

while(1)  {
   avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);
   count++;
   total_bytes += avpkt.size;

   if (avpkt.size == 0)  {
      break;
   }

   avpkt.data = inbuf;

   while (avpkt.size > 0) {
      len = avcodec_decode_video2(codec_ctx, picture, &got_picture, &avpkt);
      if (len < 0) {
         fclose(f);
         printf("Error while decoding frame %d, count = %ld,
total_bytes = %ld\n", frame, count, total_bytes);
         goto done;
      }

      if (got_picture) {
         frame++;
         if ((frame%100)==0)  {
            printf("&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
    %d\n", frame);
         }
      }
      avpkt.size -= len;
      avpkt.data += len;
   }                              // while (avpkt.size > 0)
}                                     // while(1)

avpkt.data = NULL;
avpkt.size = 0;

done:
FCLOSE(f);

if (format_ctx)  {
   //av_close_input_file(format_ctx);
   avformat_free_context(format_ctx);
}
if (codec_ctx)  {
   avcodec_close(codec_ctx);
   av_free(codec_ctx);
}
if (picture)  {
   av_free(picture);
}