On 16/07/2024 07.40, Oliver Fromme wrote:
Mark Filipak wrote:
> Since 00305.m2ts is AVC encoded, there are I slices in it but not I frames -- I
P & B frames are
> MPEG-1 & MPEG-2.
That's not completely correct. I suggest you read a bit about
basic concepts and terminology of H.264 (AVC). I'll try to
summarize it:
Thank you for your summary, Oliver. That has really, really helped. As you know, H.264 is
prescriptive, not descriptive, which makes understanding it very difficult.
It also lacks the strings: "I[- ]frame" "P[- ]frame" "B[- ]frame" "I[- ]picture" "P[- ]picture" "B[-
]picture" and "GOP.+".
I've taken my 40 second clip of a Criterion mastered video and am trying to parse it. The TS packets
are 192 bytes.
May I ask some questions?
What are the 4 bytes, 0..3, that precede the 0x47 sync byte? I can't find any documentation on them.
What can you tell me?
======================================| (unknown)__ TS_HEADER__ TS_PAYLOAD___..
0..3 unknown | HH HH HH HH
--------------------------------------| TS_HEADER__
4..7 | 47 HH HH HH
4 sync_byte | 47 == == ==
| == HH HH H=
| .——' '—————————————.
5 transport_error_indicator | b--- ---- ---- ---- ---- //1
payload_unit_start_indicator | -b-- ---- ---- ---- ---- //2
transport_priority | --b- ---- ---- ---- ---- //3
5..6 PID (Packet Identifier) | ---b bbbb bbbb bbbb ---- //4
7 transport_scrambling_control | ---- ---- ---- ---- bb-- //5
adaptation_field_control | ---- ---- ---- ---- --bb //6
continuity_counter | == == == =H //0..15, cycles
--------------------------------------| TS_PAYLOAD___..
8..191 data_byte | HH ..
======================================|
1, 0,none..1,transport reports an error
2, 0,payload continuing..1,payload starting
3, 0,none..1,for this PID, this packet has priority over those with '0'
transport_priority
4, 0,PAT..1,CAT..2,TS description table..3,IPMP..4..15,(reserved)..16..8190,network_PID
Program_map_PID elementary_PID or other..8191,packet is null -- may also convey PCR
5, 0,payload is not scrambled..1..3,(user-defined)
6, 0,(reserved)..1,has payload..2,has adaptation..3,has adaptation..payload
There is a variable number of bytes between the tags above and the first start code (that is, if
there is a start code). Do you know what those bytes are?
References or links will be okay of course--Mark.
H.264 (AVC) has I-frames, too. These frames may use only spatial
prediction, i.e. they contain only intra-predicted macroblocks.
P-frames and B-frames may use both spatial and temporal prediction,
i.e. they contain inter-predicted and intra-predicted macroblocks
(where P-frames are restricted to forward prediction, and B-frames
may use both forward and backward prediction).
Note that a slice is basically just a group of macroblocks that
describe a certain region of a frame and share some common
properties. For example, an "I-slice" is a group of macroblocks
that use only spatial prediction. And an I-frame contains only
intra-predicted slices (I-slices), while a P-frame may contain
P-slices and I-slices, and a B-frame may contain all three types
of slices.
Finally, there are IDR-frames. These are I-frames that signify
a closed GOP. That is, temporal predictions may not cross the
boundary of an IDR-frame. I-frames that are part of an open GOP
are not IDR-frames.
Best regards
-- Oliver
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