CODEWITHSUNDEEP
c++opencvvideoffmpeg
Srv19
Srv19

Reputation: 3618

How to read YUV8 data from avi file?

I have avi file that contains uncompressed gray video data. I need to extract frames from it. The size of file is 22 Gb.

How do i do that?

I have already tried ffmpeg, but it gives me "could not find codec parameters for video stream" message - because there is no codec at work, just frames.

Since Opencv just uses ffmpeg to read video, that rules out opencv as well.

The only path that seems to be left is to try and dig into the raw data, but i do not know how.

Edit: this is the code i use to read from the file with opencv. The failure occurs inside the second if. Running ffmpeg binary on the file also fails with the message above (could not find codec aprameters etc)

/* register all formats and codecs */
av_register_all();

/* open input file, and allocate format context */
if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
    fprintf(stderr, "Could not open source file %s\n", src_filename);
    ret = 1;
    goto end;
}
fmt_ctx->seek2any = true;
/* retrieve stream information */
int res = avformat_find_stream_info(fmt_ctx, NULL);
if (res < 0) {
    fprintf(stderr, "Could not find stream information\n");
    ret = 1;
    goto end;
}

Edit:

Here is sample code i have tried to make the extraction: pastebin. The result i get is an unchanging buffer after every call to AVIStreamRead.

Upvotes: 1

Views: 1469

Answers (1)

Rudolfs Bundulis
Rudolfs Bundulis

Reputation: 11954

If you do not need cross platform functionality Video for Windows (VFW) API is a good alternative (http://msdn.microsoft.com/en-us/library/windows/desktop/dd756808(v=vs.85).aspx), i will not put an entire code block, since there's quite much to do, but you should be able to figure it out from the reference link. Basically, you do a AVIFileOpen, then get the video stream via AVIFileGetStream with streamtypeVIDEO, or alternatively do it at once with AVIStreamOpenFromFile and then read samples from the stream with AVIStreamRead. If you get to a point where you fail I can try to help, but it should be pretty straightforward.

Also, not sure why ffmpeg is failing, I have been doing raw AVI reading with ffmpeg without any codecs involved, can you post what call to ffpeg actually fails?

EDIT:

For the issue that you are seeing when the read data size is 0. The AVI file has N slots for frames in each second where N is the fps of the video. In real life the samples won't come exactly at that speed (e.g. IP surveillance cameras) so the actual data sample indexes can be non continuous like 1,5,11,... and VFW would insert empty samples between them (that is from where you read a sample with a zero size). What you have to do is call AVIStreamRead with NULL as buffer and 0 as size until the bRead is not 0 or you run past last sample. When you get an actual size, then you can again call AVIStreamRead on that sample index with the buffer pointer and size. I usually do compressed video so i don't use the suggested size, but at least according to your code snipplet I would do something like this:

...
bRead = 0;
do 
{
    aviOpRes = AVIStreamRead(ppavi,smpS,1,NULL,0,&bRead,&smpN);
} while (bRead == 0 && ++smpS < si.dwLength + si.dwStart);
if(smpS >= si.dwLength + si.dwStart)
    break;
PUCHAR tempBuffer = new UCHAR[bRead];
aviOpRes = AVIStreamRead(ppavi,smpS,1,tempBuffer,bRead,&bRead,&smpN);
/* do whatever you need */
delete tempBuffer;
...

EDIT 2:

Since this may come in handy to someone or yourself to make a choice between VFW and FFMPEG I also updated your FFMPEG example so that it parsed the same file (sorry for the code quality since it lacks error checking but i guess you can see the logical flow):

/* register all formats and codecs */
av_register_all();
AVFormatContext* fmt_ctx = NULL;
/* open input file, and allocate format context */
const char *src_filename = "E:\\Output.avi";
if (avformat_open_input(&fmt_ctx, src_filename, NULL, NULL) < 0) {
    fprintf(stderr, "Could not open source file %s\n", src_filename);
    abort();
}
/* retrieve stream information */
int res = avformat_find_stream_info(fmt_ctx, NULL);
if (res < 0) {
    fprintf(stderr, "Could not find stream information\n");
    abort();
}
int video_stream_index = 0; /* video stream is usualy 0 but still better to lookup in case it's not present */
for(; video_stream_index < fmt_ctx->nb_streams; ++video_stream_index)
{
    if(fmt_ctx->streams[video_stream_index]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
        break;
}
if(video_stream_index == fmt_ctx->nb_streams)
    abort();
AVPacket *packet = new AVPacket;
while(av_read_frame(fmt_ctx, packet) == 0)
{
    if (packet->stream_index == video_stream_index)
        printf("Sample nr %d\n", packet->pts);
    av_free_packet(packet);
}

Basically you open the context and read packets from it. You will get both audio and video packets so you should check if the packet belongs to the stream of interest. FFMPEG will save you the trouble with empty frames and give only those samples that have data in them.

Upvotes: 2

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