[FFmpeg-devel] All packets are marked with PKT_FLAG_KEY when reading AVI files

[Eyal Beit-Halachmi]

Hello,
	When reading video frames from AVI files using av_read_frame(), all
packets read have their packet->flags set to PKT_FLAG_KEY
	In avidec.c,  in avi_read_header(), for CODEC_TYPE_VIDEO codec, the
"need_parsing" is set to "st->need_parsing = AVSTREAM_PARSE_HEADERS ".
	Then in utils.c, av_read_frame_internal(), the parser is initialized
and set to parse whole frames "st->parser->flags |=
PARSER_FLAG_COMPLETE_FRAMES ".

	But when setting to parse whole frames, various parsers do not parse
but rather skip to the end of frame.
	Here is h264_parse() and mpeg4_parse() code that do the skip:
	...
    	if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
		next= buf_size;
	}else{
	...

	Now, in av_read_frame_internal(), when there is a parser, the
returned packet "flags" are set by "compute_pkt_fields()", rather than by
copying the value from the packet read by avi_read_packet().
	Now, because the parser did not parse the frame, its key_frame and
pict_type are the defaults -1 and FF_I_TYPE respectively, and the packet is
always marked as KEY (as seen from the code below).

void compute_pkt_fields(AVFormatContext *s, AVStream *st,
AVCodecParserContext *pc, AVPacket *pkt)
{
	...
	/* update flags */
	if(is_intra_only(st->codec))
		pkt->flags |= PKT_FLAG_KEY;
	else if (pc) {
		pkt->flags = 0;
		/* keyframe computation */
		if (pc->key_frame == 1)
			pkt->flags |= PKT_FLAG_KEY;
		else if (pc->key_frame == -1 && pc->pict_type == FF_I_TYPE)
			pkt->flags |= PKT_FLAG_KEY;
	}
	...
}

	I have added code handling the PARSER_FLAG_COMPLETE_FRAMES case,
setting the packet flags by the read packets' ones:
	...
	else if (pc) {
		pkt->flags = 0;
		//Added code
		if(pc->flags & PARSER_FLAG_COMPLETE_FRAMES)
			pkt->flags = st->cur_pkt.flags;
		else
		//Added code
		if (pc->key_frame == 1)
			pkt->flags |= PKT_FLAG_KEY;
		else if (pc->key_frame == -1 && pc->pict_type == FF_I_TYPE)
			pkt->flags |= PKT_FLAG_KEY;
	}
	...

Eyal.