Indeo 5

• FOURCCs: IV50
• Company: Intel, then Ligos
• Samples: http://www.mplayerhq.hu/MPlayer/samples/V-codecs/IV50/

General description

Frame layout

The general indeo5 frames layout is composed of one global header, followed by the content of the three YUV plans.

In this document, the global header is split into 3 parts:

• Frame header: describe the kind of frame (I/P/B)
• GOP header: some data which is true for all the frame in this GOP (present only in the first (I) frame of the GOP)
• More header: some more data which is true only for this single frame

Each YUV plan begin with a Plan header, containing values which are valid only for this single plan.

Encoding

This codec is based on the slant transform. Other used standard techniques are huffman coding and motion compensation.

Conventions

Headers are described in some tables. Each row of those tables describes a value which may be read from the frame. Those tables and rows are presented in the order of appearance in the frame.

Here are the meaning of each columns:

• size: The size of this value in bits. Bits are counted in MSB to LSB order. As an example, with the byte 01110000b, reading 3 bits then 5 bits will return 011b then 10000b.
• name: Kind of variable name, used to reference the value. When a value is named valueX, it generally means we don't know it's purpose. Lines named alignmentX means that bits reader need to skip bits until next byte boundary.
• condition: The value is present in the frame only if this condition is matched. No condition means that the value is always present.
• nb times: How many times the value is repeated.
• comments: Some details about the content of the value. It may also explain that a value is repeated until a certain condition is reached.

Headers

Frame header

size	name	condition	nb times	comments
3	frame_flags			frame_flags & 0x01 => backward predictive frame_flags & 0x02 => forward predictive frame_flags & 0x04 => null frame common values: 0 => I frame 1 => P frame 3 => B frame
5	const1			= 0x1F always
8	id_in_gop			frame number in GOP (0 for I frame)

null frames don't contain anything else than this header.

GOP header

This header is present in I frames only. The values in this header are valid during the whole GOP starting at this frame.

size	name	condition	nb times	comments
8	gh_flags			gh_flags & 0x02 => YV12 (default YVU9)
16	value1	gh_flags & 0x01
32	value2	gh_flags & 0x20
2	value3	gh_flags & 0x40
3	value4
4	res_id			see Resolution table
13	height	res_id == 15		frame height
13	width			frame width
6	value5		2*n (n == 1 always?)
2	value6	value5 >> 3		need to be = 0
4	value7	gh_flags & 0x08
24	value8
??	alignment1			align bits reader on next byte
24	value9
16	value10	value9 & 0x800000		loops while value10 & 0x8000 (probably some kind of VLC ?)

More header

This header is present in all kinds of frame except null.

size	name	condition	nb times	comments
8	mh_flags
24	frame_size	mh_flags & 0x01		tolal size of frame data
16	value11	mh_flags & 0x10
8	counter1	mh_flags & 0x20		this whole block loops while counter1 != 0
8	value12		counter1
3	value13	mh_flags & 0x40
4	counter2	value13 == 7
4	value14		counter2
3	value15
??	alignment2			align bits reader on next byte

Plan header

This header is present at the beginning of every plan.

size	name	condition	nb times	comments
8	ph_flags
24	plan_size	mh_flags & 0x80		tolal size of plan data
8	counter3	ph_flags & 0x10		must be < 0x3E
8	value16		counter3
8	value17
3	value18	ph_flags & 0x40
3	table1_id	ph_flags & 0x80		see Table 1
4	counter4	table1_id == 7		used instead of Table1
4	value19		counter4
1	value20
16	value21	value20
5	value22
??	alignment3			align bits reader on next byte
8	counter5	ph_flags & 0x20		all of this is repeated as long as value23 is true
8	skip1		counter5
1	value23
??	alignment4			align bits reader on next byte

Plan data

This is where the actual data is, but this still need to be reverse engineered :-(

size	name	condition	nb times	comments
1	value24
1	value25	! value24		plan_data_size = value25
8	value26	value25 == 1		plan_data_size = value26
24	value27	value26 == 0xFF		plan_data_size = value27
??	...			more data to analyze

Annexes

Resolution table

res_id	0	1	2	3	4	5	6	7	8	9	10	11
width	640	320	160	704	352	352	176	240	640	704	80	88
height	480	240	120	224	240	288	144	180	240	240	60	72

Table 1

table1_id	0	1	2	3	4	5	6	default
counter4	10	11	12	13	11	13	13	9
value19	1 2 3 4 4 7 5 5 4 1	2 3 4 4 4 7 5 4 3 3 2	2 4 5 5 5 5 6 4 4 3 1 1	3 3 4 4 5 6 6 4 4 3 2 1 1	3 4 4 5 5 5 6 5 4 2 2	3 4 5 5 5 5 6 4 3 3 2 1 1	3 4 5 5 5 6 5 4 3 3 2 1 1	3 4 4 5 5 5 6 5 5

default is used when !(ph_flags & 0x80)