Re: [mpeg2-dev] mpeg2_parse always returns STATE_INVALID

[Daniel T. <dt....@gm...>]

I've debugged it a bit an I think I've found the problem.

I did some comparing between my copy of libmpeg compiled for my computer and the compiled copy for my ARM processor. 

I found that STATE_INTERNAL_NORETURN was defined as ((mpeg2_state_t)-1). On x86 processors, gcc makes the mpeg2_state_t enumeration a signed type while on my ARM processor, it's an unsigned type. So, because -1 is cast to an unsigned type, it's value (in my case) was 255 instead of -1. That probably was the reason why it worked on my computer and not my ARM processor. I simply changed the cast to a signed character type and recompiled.

Now, I'm getting, presumably, a stack overflow somewhere on the second call to mpeg_parse() (after calling mpeg_buffer()). If anyone can shed some light, that would be great.


On 15/06/2011, at 4:38 PM, Daniel Tang wrote:

> Hi,
> 
> I've just compiled libmpeg2 for an embedded platform and have written some code for decoding. But the call to mpeg2_parse in this code seems to always return STATE_INVALID. 
> 
> int play(FILE * mpgfile)
> {
> 	mpeg2dec_t * decoder;
>   const mpeg2_info_t * info;
>   mpeg2_state_t state;
>   size_t size = 1;
> 	unsigned char *buffer = malloc(BUFFER_SIZE);
> 	
> 	char debug[20];
> 	if (!buffer) {
> 		show_msgbox("NspireMoviePlayer","NULL ptr from Malloc");
> 		return 1;
> 	}
> 	
> 	decoder = mpeg2_init ();
>   if (!decoder) {
>   	show_msgbox("NspireMoviePlayer","Could not init mpeg2");
> 		return 1;
> 	}
> 
>   info = mpeg2_info (decoder);
> 	do
> 	{
> 		state = mpeg2_parse (decoder);
> 		switch (state) {
> 			case STATE_BUFFER:
> 		    	size = fread (buffer, 1, BUFFER_SIZE, mpgfile);
> 		    	mpeg2_buffer (decoder, buffer, buffer + size);
> 		    	break;
> 			case STATE_SEQUENCE:
> 		    	mpeg2_convert (decoder, mpeg2convert_rgb24, NULL);
> 		    	settimerperiod(info->sequence->frame_period);
> 		    	break;
> 			case STATE_SLICE:
> 			case STATE_END:
> 				if (info->sequence->width  != SCREEN_WIDTH ||
> 					info->sequence->height != SCREEN_HEIGHT)
> 				{
> 					show_msgbox("NspireMoviePlayer","Screen size mismatch");
> 					goto die;
> 				}
> 				else {
> 					waittimerperiod();
> 					renderframe(info->display_fbuf->buf[0]);
> 				}
> 				break;
> 			case STATE_INVALID:
> 				goto die;
> 		    	break;
> 			default:
> 		    	break;
> 		}
> 	} while(size);
> 	
> 	mpeg2_close(decoder);
> 	return 0;
> 	
> 	die:
> 	mpeg2_close(decoder);
> 	return 1;
> }
> 
> I dug around decode.c and added some debugging messages and it seems it's conking out in this piece of code at the bottom of mpeg2_parse:
> 
> mpeg2dec->action = mpeg2_seek_header;
>   switch (mpeg2dec->code) {
>   case 0x00:
>   show_msgbox("libmpeg2","case 0 mpeg2dec->code");
> 	return mpeg2dec->state;
>   case 0xb3:
>   case 0xb7:
>   case 0xb8:
>   show_msgbox("libmpeg2","case b8 mpeg2dec->code");
> 	return (mpeg2dec->state == STATE_SLICE) ? STATE_SLICE : STATE_INVALID;
>   default:
> 	mpeg2dec->action = seek_chunk;
> 	show_msgbox("libmpeg2","default mpeg2dec->code"); // This is where it returns
> 	return STATE_INVALID;
>   }
> 
> Does anyone have any ideas on what could be causing this? The code isn't very well documented and it's hard to follow.
> 
> Cheers,