There is one way to find out if avpriv_find_start_code has found a start
code or not: One has to check whether the state variable contains a
start code, i.e. whether the three most significant bytes are 0x00 00 01.
Checking for whether the return value is the end of the designated
buffer is not enough: If the last four bytes constitute a start code,
the return value is also the end of the buffer. This happens with
sequence_end_codes which have been ignored for exactly this reason,
although e.g. all three files used for fate tests of cbs_mpeg2 contain
sequence_end_codes.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
1. Currently, cbs_mpeg2_split_fragment uses essentially three variables
to hold the start code values found by avpriv_find_start_code. By
rearranging the code, one of them can be omitted.
2. The return value of avpriv_find_start_code points to the byte after
the byte containing the start code identifier (or to the byte after the
last byte of the fragment's data if no start code was found), but
cbs_mpeg2_split_fragment needs to work with the pointer to the byte
containing the start code identifier; it already did this, but in a
clumsy way. This has been changed.
3. Also use the correct type for the variable holding the
CodedBitstreamUnitType.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Sequence End units (or actually, sequence_end_codes) have up until now
not been decomposed; in fact due to a bug in cbs_mpeg2_split_fragment they
have mostly been treated as part of the preceding unit. So implement
decomposing them as preparation for fixing said bug.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
cbs is currently inconsistent regarding the opaque field that can be
used as a special argument to av_buffer_create in order to be used
during freeing the buffer: ff_cbs_alloc_unit_content and all the free
functions used name this parameter as if it should contain a pointer to
the unit whose content is about to be created; but both
ff_cbs_alloc_unit_content as well as ff_cbs_h264_add_sei_message
actually use a pointer to the CodedBitstreamContext as opaque. It should
actually be neither, because it is unneeded (as is evidenced by the fact
that none of the free functions use this pointer at all) and because it
ties the unit's content to the lifetime of other objects, although a
refcounted buffer is supposed to have its own lifetime that only ends
when its reference count reaches zero. This problem manifests itself in
the pointer becoming dangling.
The pointer to the unit can become dangling if another unit is added to
the fragment later as happens in the bitstream filters; in this case,
the pointer can point to the wrong unit (if the fragment's unit array
needn't be relocated) or it can point to where the array was earlier.
It can also become dangling if the unit's content is meant to survive
the resetting of the fragment it was originally read with. This applies
to the extradata of H.264 and HEVC.
The pointer to the context can become dangling if the context is closed
before the content is freed. Although this doesn't seem to happen right
now, it could happen, in particular if one uses different
CodedBitstreamContexts for in- and output.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
1. The extra information in slice headers was parsed incorrectly:
In the first reading pass to derive the length of the extra information,
one should look at bits n, n + 9, n + 18, ... and check whether they
equal one (further extra information) or zero (end of extra information),
but instead bits n, n + 8, n + 16, ... were inspected. The second pass
of reading (where the length is already known and the bytes between the
length-determining bits are copied into a buffer) did not record what
was in bits n, n + 9, n + 18, ..., presuming they equal one. And during
writing, the bytes in the buffer are interleaved with set bits and
written. This means that if the detected length of the extra information
was greater than the real length, the output was corrupted. Fortunately
no sample is known that made use of this mechanism: The extra information
in slices is still marked as reserved in the specifications. cbs_mpeg2
is now ready in case this changes.
2. Furthermore, the buffer is now padded and slightly different, but
very similar code for reading resp. writing has been replaced by code
used for both. This was made possible by a new macro, the equivalent
to cbs_h2645's fixed().
3. These changes also made it possible to remove the extra_bit_slice
element from the MPEG2RawSliceHeader structure. Said element was always
zero except when the detected length of the extra information was less
than the real length.
4. The extra information in picture headers (which uses essentially the
same syntax as the extra information in slice headers) has simply been
forgotten. This meant that if this extra information was present, it was
discarded during reading; and unfortunately writing created invalid
bitstreams in this case (an extra_bit_picture - the last set bit of the
whole unit - indicated that there would be a further byte of data,
although the output didn't contain said data).
This has been fixed; both types of extra information are now parsed via
the same code and essentially passed through.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Up until now, a temporary variable was used and initialized every time a
value was read in CBS; if reading turned out to be successfull, this
value was overwritten (without having ever been looked at) with the
value read if reading was successfull; on failure the variable wasn't
touched either. Therefore these initializations can be and have been
removed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
If a sequence display extension is read with colour_description equal to
zero, but a user wants to add one or more of the colour_description
elements, then the colour_description elements the user did not explicitly
request to be set are set to zero and not to the value equal to
unknown/unspecified (namely 2). A value of zero is not only inappropriate,
but explicitly forbidden. This is fixed by inferring the right default
values during the reading process if the elements are absent; moreover,
changing any of the colour_description elements to zero is now no longer
possible.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
READ has already been undefined at this point; it is obviously intended
to undef WRITE.
Furthermore, leb128 (in cbs_av1) was undefined too often and
inconsistently.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Up until now, things that are merely unsupported by cbs_mpeg2 have been
declared to be invalid input. This has been changed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The frame_centre_horizontal/vertical_offset values contained in picture
display extensions are actually signed values (i.e. it is possible to
indicate that the display device should add black bars/pillars).
The files sony-ct3.bs and tcela-6.bits (which are both used in fate
tests for mpeg2_metadata) contain picture display extensions; the former
even contains a negative frame_centre_vertical_offset. Fortunately, the
old code did not damage the picture display extensions when one did a
cycle of reading and writing. For the same reason the fate tests needn't
be updated either.
Furthermore these fields now use the trace output for matrices.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
MPEG-2 contains several elements that mustn't be zero according to the
specifications: horizontal/vertical_size_value, aspect_ratio_information,
frame_rate_code, the quantiser matrices, the colour_description
elements, picture_coding_type, the f_code[r][s] values and
quantiser_scale_code. It is now checked that the invalid values don't
occur.
The colour_description elements are treated specially in this regard:
Given that there are files in the wild which use illegal values for the
colour_description elements (some of them created by mpeg2_metadata),
they will be corrected to the value meaning "unknown" (namely 2) during
reading. This has been done in such a way that trace_headers will
nevertheless report the original value, together with a message about
the fixup.
Furthermore, the trace_headers output of user_data has been beautified.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Instead of using a combination of bitreader and -writer for copying data,
one can byte-align the (obsolete and removed) bitreader to improve performance.
One can even use memcpy in the normal case.
This improved the time needed for writing the slicedata from 33618 to
2370 decicycles when tested on a video originating from a DVD (4194394
runs).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@googlemail.com>
Signed-off-by: Mark Thompson <sw@jkqxz.net>
before:
419022 decicycles in assemble_fragment, 2047 runs, 1 skips
after:
104621 decicycles in assemble_fragment, 2045 runs, 3 skips
Benched with a 2 minutes long 720x480 DVD mpeg2 sample.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: James Almer <jamrial@gmail.com>
This saves one malloc + memcpy per packet
The CodedBitstreamFragment buffer is padded to follow the requirements
of AVPacket.
Reviewed-by: jkqxz
Signed-off-by: James Almer <jamrial@gmail.com>
This makes it easier for users of the CBS API to get alloc/free right -
all subelements use the buffer API so that it's clear how to free them.
It also allows eliding some redundant copies: the packet -> fragment copy
disappears after this change if the input packet is refcounted, and more
codec-specific cases are now possible (but not included in this patch).
Andreas Rheinhardt
Andreas Rheinhardt
Mark Thompson
James Almer
Carl Eugen Hoyos