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ffmpeg-rockchip/libavcodec/cbs_mpeg2.c
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Andreas Rheinhardt 115ac90ec9 avcodec/cbs_mpeg2: Simplify splitting fragment 
avpriv_find_start_code() supports non-contiguous buffers
by maintaining a state that allows to find start codes
that span across multiple buffers; a consequence thereof
is that avpriv_find_start_code() is given a zero-sized
buffer, it does not modify this state, so that it appears
as if a start code was found if the state contained a start code.

This can e.g. happen with Sequence End units in MPEG-2 and
to counter this, cbs_mpeg2_split_fragment() reset the state
when it has already encountered the end of the fragment
in order to add the last unit (if it is only of the form 00 00 01 xy)
only once; it also used a flag to set whether this is the final unit.

Yet this can be improved by simply resetting state unconditionally
(thereby avoiding a branch); the flag can be removed by just checking
whether we have a valid start code (of the next unit to add)
at the end.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
2022-02-08 06:10:08 +01:00

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/*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "libavutil/avassert.h"
#include "cbs.h"
#include "cbs_internal.h"
#include "cbs_mpeg2.h"
#include "internal.h"
#define HEADER(name) do { \
ff_cbs_trace_header(ctx, name); \
} while (0)
#define CHECK(call) do { \
err = (call); \
if (err < 0) \
return err; \
} while (0)
#define FUNC_NAME(rw, codec, name) cbs_ ## codec ## _ ## rw ## _ ## name
#define FUNC_MPEG2(rw, name) FUNC_NAME(rw, mpeg2, name)
#define FUNC(name) FUNC_MPEG2(READWRITE, name)
#define SUBSCRIPTS(subs, ...) (subs > 0 ? ((int[subs + 1]){ subs, __VA_ARGS__ }) : NULL)
#define ui(width, name) \
xui(width, name, current->name, 0, MAX_UINT_BITS(width), 0, )
#define uir(width, name) \
xui(width, name, current->name, 1, MAX_UINT_BITS(width), 0, )
#define uis(width, name, subs, ...) \
xui(width, name, current->name, 0, MAX_UINT_BITS(width), subs, __VA_ARGS__)
#define uirs(width, name, subs, ...) \
xui(width, name, current->name, 1, MAX_UINT_BITS(width), subs, __VA_ARGS__)
#define xui(width, name, var, range_min, range_max, subs, ...) \
xuia(width, #name, var, range_min, range_max, subs, __VA_ARGS__)
#define sis(width, name, subs, ...) \
xsi(width, name, current->name, subs, __VA_ARGS__)
#define marker_bit() \
bit("marker_bit", 1)
#define bit(string, value) do { \
av_unused uint32_t bit = value; \
xuia(1, string, bit, value, value, 0, ); \
} while (0)
#define READ
#define READWRITE read
#define RWContext GetBitContext
#define xuia(width, string, var, range_min, range_max, subs, ...) do { \
uint32_t value; \
CHECK(ff_cbs_read_unsigned(ctx, rw, width, string, \
SUBSCRIPTS(subs, __VA_ARGS__), \
&value, range_min, range_max)); \
var = value; \
} while (0)
#define xsi(width, name, var, subs, ...) do { \
int32_t value; \
CHECK(ff_cbs_read_signed(ctx, rw, width, #name, \
SUBSCRIPTS(subs, __VA_ARGS__), &value, \
MIN_INT_BITS(width), \
MAX_INT_BITS(width))); \
var = value; \
} while (0)
#define nextbits(width, compare, var) \
(get_bits_left(rw) >= width && \
(var = show_bits(rw, width)) == (compare))
#define infer(name, value) do { \
current->name = value; \
} while (0)
#include "cbs_mpeg2_syntax_template.c"
#undef READ
#undef READWRITE
#undef RWContext
#undef xuia
#undef xsi
#undef nextbits
#undef infer
#define WRITE
#define READWRITE write
#define RWContext PutBitContext
#define xuia(width, string, var, range_min, range_max, subs, ...) do { \
CHECK(ff_cbs_write_unsigned(ctx, rw, width, string, \
SUBSCRIPTS(subs, __VA_ARGS__), \
var, range_min, range_max)); \
} while (0)
#define xsi(width, name, var, subs, ...) do { \
CHECK(ff_cbs_write_signed(ctx, rw, width, #name, \
SUBSCRIPTS(subs, __VA_ARGS__), var, \
MIN_INT_BITS(width), \
MAX_INT_BITS(width))); \
} while (0)
#define nextbits(width, compare, var) (var)
#define infer(name, value) do { \
if (current->name != (value)) { \
av_log(ctx->log_ctx, AV_LOG_WARNING, "Warning: " \
"%s does not match inferred value: " \
"%"PRId64", but should be %"PRId64".\n", \
#name, (int64_t)current->name, (int64_t)(value)); \
} \
} while (0)
#include "cbs_mpeg2_syntax_template.c"
#undef WRITE
#undef READWRITE
#undef RWContext
#undef xuia
#undef xsi
#undef nextbits
#undef infer
static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
CodedBitstreamFragment *frag,
int header)
{
const uint8_t *start, *end;
CodedBitstreamUnitType unit_type;
uint32_t start_code = -1;
size_t unit_size;
int err;
start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,
&start_code);
if (start_code >> 8 != 0x000001) {
// No start code found.
return AVERROR_INVALIDDATA;
}
do {
unit_type = start_code & 0xff;
// Reset start_code to ensure that avpriv_find_start_code()
// really reads a new start code and does not reuse the old
// start code in any way (as e.g. happens when there is a
// Sequence End unit at the very end of a packet).
start_code = UINT32_MAX;
end = avpriv_find_start_code(start--, frag->data + frag->data_size,
&start_code);
// start points to the byte containing the start_code_identifier
// (may be the last byte of fragment->data); end points to the byte
// following the byte containing the start code identifier (or to
// the end of fragment->data).
if (start_code >> 8 == 0x000001) {
// Unit runs from start to the beginning of the start code
// pointed to by end (including any padding zeroes).
unit_size = (end - 4) - start;
} else {
// We didn't find a start code, so this is the final unit.
unit_size = end - start;
}
err = ff_cbs_append_unit_data(frag, unit_type, (uint8_t*)start,
unit_size, frag->data_ref);
if (err < 0)
return err;
start = end;
// Do we have a further unit to add to the fragment?
} while ((start_code >> 8) == 0x000001);
return 0;
}
static int cbs_mpeg2_read_unit(CodedBitstreamContext *ctx,
CodedBitstreamUnit *unit)
{
GetBitContext gbc;
int err;
err = init_get_bits(&gbc, unit->data, 8 * unit->data_size);
if (err < 0)
return err;
err = ff_cbs_alloc_unit_content2(ctx, unit);
if (err < 0)
return err;
if (MPEG2_START_IS_SLICE(unit->type)) {
MPEG2RawSlice *slice = unit->content;
int pos, len;
err = cbs_mpeg2_read_slice_header(ctx, &gbc, &slice->header);
if (err < 0)
return err;
if (!get_bits_left(&gbc))
return AVERROR_INVALIDDATA;
pos = get_bits_count(&gbc);
len = unit->data_size;
slice->data_size = len - pos / 8;
slice->data_ref = av_buffer_ref(unit->data_ref);
if (!slice->data_ref)
return AVERROR(ENOMEM);
slice->data = unit->data + pos / 8;
slice->data_bit_start = pos % 8;
} else {
switch (unit->type) {
#define START(start_code, type, read_func, free_func) \
case start_code: \
{ \
type *header = unit->content; \
err = cbs_mpeg2_read_ ## read_func(ctx, &gbc, header); \
if (err < 0) \
return err; \
} \
break;
START(MPEG2_START_PICTURE, MPEG2RawPictureHeader,
picture_header, &cbs_mpeg2_free_picture_header);
START(MPEG2_START_USER_DATA, MPEG2RawUserData,
user_data, &cbs_mpeg2_free_user_data);
START(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader,
sequence_header, NULL);
START(MPEG2_START_EXTENSION, MPEG2RawExtensionData,
extension_data, NULL);
START(MPEG2_START_GROUP, MPEG2RawGroupOfPicturesHeader,
group_of_pictures_header, NULL);
START(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd,
sequence_end, NULL);
#undef START
default:
return AVERROR(ENOSYS);
}
}
return 0;
}
static int cbs_mpeg2_write_header(CodedBitstreamContext *ctx,
CodedBitstreamUnit *unit,
PutBitContext *pbc)
{
int err;
switch (unit->type) {
#define START(start_code, type, func) \
case start_code: \
err = cbs_mpeg2_write_ ## func(ctx, pbc, unit->content); \
break;
START(MPEG2_START_PICTURE, MPEG2RawPictureHeader, picture_header);
START(MPEG2_START_USER_DATA, MPEG2RawUserData, user_data);
START(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader, sequence_header);
START(MPEG2_START_EXTENSION, MPEG2RawExtensionData, extension_data);
START(MPEG2_START_GROUP, MPEG2RawGroupOfPicturesHeader,
group_of_pictures_header);
START(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd, sequence_end);
#undef START
default:
av_log(ctx->log_ctx, AV_LOG_ERROR, "Write unimplemented for start "
"code %02"PRIx32".\n", unit->type);
return AVERROR_PATCHWELCOME;
}
return err;
}
static int cbs_mpeg2_write_slice(CodedBitstreamContext *ctx,
CodedBitstreamUnit *unit,
PutBitContext *pbc)
{
MPEG2RawSlice *slice = unit->content;
int err;
err = cbs_mpeg2_write_slice_header(ctx, pbc, &slice->header);
if (err < 0)
return err;
if (slice->data) {
size_t rest = slice->data_size - (slice->data_bit_start + 7) / 8;
uint8_t *pos = slice->data + slice->data_bit_start / 8;
av_assert0(slice->data_bit_start >= 0 &&
slice->data_size > slice->data_bit_start / 8);
if (slice->data_size * 8 + 8 > put_bits_left(pbc))
return AVERROR(ENOSPC);
// First copy the remaining bits of the first byte
if (slice->data_bit_start % 8)
put_bits(pbc, 8 - slice->data_bit_start % 8,
*pos++ & MAX_UINT_BITS(8 - slice->data_bit_start % 8));
if (put_bits_count(pbc) % 8 == 0) {
// If the writer is aligned at this point,
// memcpy can be used to improve performance.
// This is the normal case.
flush_put_bits(pbc);
memcpy(put_bits_ptr(pbc), pos, rest);
skip_put_bytes(pbc, rest);
} else {
// If not, we have to copy manually:
for (; rest > 3; rest -= 4, pos += 4)
put_bits32(pbc, AV_RB32(pos));
for (; rest; rest--, pos++)
put_bits(pbc, 8, *pos);
// Align with zeros
put_bits(pbc, 8 - put_bits_count(pbc) % 8, 0);
}
}
return 0;
}
static int cbs_mpeg2_write_unit(CodedBitstreamContext *ctx,
CodedBitstreamUnit *unit,
PutBitContext *pbc)
{
if (MPEG2_START_IS_SLICE(unit->type))
return cbs_mpeg2_write_slice (ctx, unit, pbc);
else
return cbs_mpeg2_write_header(ctx, unit, pbc);
}
static int cbs_mpeg2_assemble_fragment(CodedBitstreamContext *ctx,
CodedBitstreamFragment *frag)
{
uint8_t *data;
size_t size, dp;
int i;
size = 0;
for (i = 0; i < frag->nb_units; i++)
size += 3 + frag->units[i].data_size;
frag->data_ref = av_buffer_alloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
if (!frag->data_ref)
return AVERROR(ENOMEM);
data = frag->data_ref->data;
dp = 0;
for (i = 0; i < frag->nb_units; i++) {
CodedBitstreamUnit *unit = &frag->units[i];
data[dp++] = 0;
data[dp++] = 0;
data[dp++] = 1;
memcpy(data + dp, unit->data, unit->data_size);
dp += unit->data_size;
}
av_assert0(dp == size);
memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
frag->data = data;
frag->data_size = size;
return 0;
}
static const CodedBitstreamUnitTypeDescriptor cbs_mpeg2_unit_types[] = {
CBS_UNIT_TYPE_INTERNAL_REF(MPEG2_START_PICTURE, MPEG2RawPictureHeader,
extra_information_picture.extra_information),
{
.nb_unit_types = CBS_UNIT_TYPE_RANGE,
.unit_type_range_start = 0x01,
.unit_type_range_end = 0xaf,
.content_type = CBS_CONTENT_TYPE_INTERNAL_REFS,
.content_size = sizeof(MPEG2RawSlice),
.nb_ref_offsets = 2,
.ref_offsets = { offsetof(MPEG2RawSlice, header.extra_information_slice.extra_information),
offsetof(MPEG2RawSlice, data) },
},
CBS_UNIT_TYPE_INTERNAL_REF(MPEG2_START_USER_DATA, MPEG2RawUserData,
user_data),
CBS_UNIT_TYPE_POD(MPEG2_START_SEQUENCE_HEADER, MPEG2RawSequenceHeader),
CBS_UNIT_TYPE_POD(MPEG2_START_EXTENSION, MPEG2RawExtensionData),
CBS_UNIT_TYPE_POD(MPEG2_START_SEQUENCE_END, MPEG2RawSequenceEnd),
CBS_UNIT_TYPE_POD(MPEG2_START_GROUP, MPEG2RawGroupOfPicturesHeader),
CBS_UNIT_TYPE_END_OF_LIST
};
const CodedBitstreamType ff_cbs_type_mpeg2 = {
.codec_id = AV_CODEC_ID_MPEG2VIDEO,
.priv_data_size = sizeof(CodedBitstreamMPEG2Context),
.unit_types = cbs_mpeg2_unit_types,
.split_fragment = &cbs_mpeg2_split_fragment,
.read_unit = &cbs_mpeg2_read_unit,
.write_unit = &cbs_mpeg2_write_unit,
.assemble_fragment = &cbs_mpeg2_assemble_fragment,
};
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