Posts: 6
Joined: Wed Aug 14, 2013 5:34 pm

Order of operations for video encoding

Mon Mar 25, 2019 1:28 pm

Hi all,

I'm in a bit of a pickle to try to understand how the video encoding process should work. Sorry if this question has already been covered before, I just couldn't find any reasonable thread here about it.

What I'm doing is:

Code: Select all

//... All the init & enable code...
//then a loop which does:
while (1) {
      buf = ilclient_get_input_buffer(private_data->video_encode, 200, 1);
      // check if buf is not null...
      memcpy(buf->pBuffer, my_raw_frame, my_raw_frame_size);
      buf->nFilledLen = my_raw_frame_size;
      if (OMX_EmptyThisBuffer(ILC_GET_HANDLE(private_data->video_encode), buf) != OMX_ErrorNone) {
          // Handle error
       out = ilclient_get_output_buffer(private_data->video_encode, 201, 1);
       r = OMX_FillThisBuffer(ILC_GET_HANDLE(private_data->video_encode), out);
       // Check if r != OMX_ErrorNone
       // Check if out == NULL
       // Check if out->nFilledLen == 0
       memcpy(my_nal_output, out->pBuffer, out->nFilledLen);
       out->nFilledLen = 0;
       // do whatever with my_nal_output   
However, it seems that out->nFilledLen is always 0?
When I looked at the example of hello_encode.c, this is the order of operations, however when I looked some other examples/code online, I can see that there are cases where the buffer is handled "between" the ilclient_get_output_buffer and the OMX_FillThisBuffer.

I also saw that there are some callbacks in order to know if the component has processed the input/output buffer, however, when I looked at the ilclient code, I saw that it already handles that callback and when block=1 then it should only return data that's available.
Is this assumption completely wrong?

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Raspberry Pi Engineer & Forum Moderator
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Joined: Wed Dec 04, 2013 11:27 am
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Re: Order of operations for video encoding

Mon Mar 25, 2019 3:10 pm

OMX_FillThisBuffer submits a buffer for filling. You must wait for the OMX_FillThisBufferDone callback (potentially handled by ilclient on your behalf) before looking at the buffer header again. Dcoumented in section of the IL spec.
Likewise OMX_EmptyThisBuffer submits a buffer for emptying, and you must wait for OMX_EmptyThisBufferDone before putting more data into the buffer. Documented in section of the spec.

hello_encode follows the correct pattern. ... ode.c#L258

Code: Select all

         out = ilclient_get_output_buffer(video_encode, 201, 1);

         if (out != NULL) {
            if (out->nFlags & OMX_BUFFERFLAG_CODECCONFIG) {
               int i;
               for (i = 0; i < out->nFilledLen; i++)
                  printf("%x ", out->pBuffer[i]);

            r = fwrite(out->pBuffer, 1, out->nFilledLen, outf);
            if (r != out->nFilledLen) {
               printf("fwrite: Error emptying buffer: %d!\n", r);
            } else {
               printf("Writing frame %d/%d, len %u\n", framenumber, NUMFRAMES, out->nFilledLen);
            out->nFilledLen = 0;
         } else {
            printf("Not getting it :(\n");

         r = OMX_FillThisBuffer(ILC_GET_HANDLE(video_encode), out);
         if (r != OMX_ErrorNone) {
            printf("Error sending buffer for filling: %x\n", r);
It is true that it did things in the wrong, but that was fixed July 2018 with ... d7b85664c5
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

Posts: 6
Joined: Wed Aug 14, 2013 5:34 pm

Re: Order of operations for video encoding

Mon Mar 25, 2019 8:10 pm

Thanks, appreciate the reply 6by9! Indeed, flipping around the order has solved the issue for me!

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