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FFmpeg/libavcodec/mpegvideo_parser.c
Anton Khirnov 4a376f45ab lavc/mpegvideo_parser: improve exporting field-coding information 
* export AVCodecParserContext.picture_structure.
* when there are two field pictures in the packet, set
  the interlacing parameters accordingly:
        * repeat_pict=1 and picture_structure=FRAME to indicate 2 fields
        * field_order to indicate the first field of the two
2023-10-03 16:57:02 +02:00

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/*
* MPEG-1 / MPEG-2 video parser
* Copyright (c) 2000,2001 Fabrice Bellard
* Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
*
* 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 "decode.h"
#include "parser.h"
#include "mpeg12.h"
#include "mpeg12data.h"
#include "startcode.h"
struct MpvParseContext {
ParseContext pc;
AVRational frame_rate;
int progressive_sequence;
int width, height;
};
/**
* Find the end of the current frame in the bitstream.
* @return the position of the first byte of the next frame, or -1
*/
static int mpeg1_find_frame_end(ParseContext *pc, const uint8_t *buf,
int buf_size, AVCodecParserContext *s)
{
int i;
uint32_t state = pc->state;
/* EOF considered as end of frame */
if (buf_size == 0)
return 0;
/*
0 frame start -> 1/4
1 first_SEQEXT -> 0/2
2 first field start -> 3/0
3 second_SEQEXT -> 2/0
4 searching end
*/
for (i = 0; i < buf_size; i++) {
av_assert1(pc->frame_start_found >= 0 && pc->frame_start_found <= 4);
if (pc->frame_start_found & 1) {
if (state == EXT_START_CODE && (buf[i] & 0xF0) != 0x80)
pc->frame_start_found--;
else if (state == EXT_START_CODE + 2) {
if ((buf[i] & 3) == 3)
pc->frame_start_found = 0;
else
pc->frame_start_found = (pc->frame_start_found + 1) & 3;
}
state++;
} else {
i = avpriv_find_start_code(buf + i, buf + buf_size, &state) - buf - 1;
if (pc->frame_start_found == 0 && state >= SLICE_MIN_START_CODE && state <= SLICE_MAX_START_CODE) {
i++;
pc->frame_start_found = 4;
}
if (state == SEQ_END_CODE) {
pc->frame_start_found = 0;
pc->state = -1;
return i + 1;
}
if (pc->frame_start_found == 2 && state == SEQ_START_CODE)
pc->frame_start_found = 0;
if (pc->frame_start_found < 4 && state == EXT_START_CODE)
pc->frame_start_found++;
if (pc->frame_start_found == 4 && (state & 0xFFFFFF00) == 0x100) {
if (state < SLICE_MIN_START_CODE || state > SLICE_MAX_START_CODE) {
pc->frame_start_found = 0;
pc->state = -1;
return i - 3;
}
}
if (pc->frame_start_found == 0 && s && state == PICTURE_START_CODE) {
ff_fetch_timestamp(s, i - 3, 1, i > 3);
}
}
}
pc->state = state;
return END_NOT_FOUND;
}
static void mpegvideo_extract_headers(AVCodecParserContext *s,
AVCodecContext *avctx,
const uint8_t *buf, int buf_size)
{
struct MpvParseContext *pc = s->priv_data;
const uint8_t *buf_end = buf + buf_size;
int bytes_left;
int did_set_size=0;
int set_dim_ret = 0;
int bit_rate = 0;
int vbv_delay = 0;
enum AVPixelFormat pix_fmt = AV_PIX_FMT_NONE;
// number of picture coding extensions (i.e. MPEG2 pictures)
// in this packet - should be 1 or 2
int nb_pic_ext = 0;
// when there are two pictures in the packet this indicates
// which field is in the first of them
int first_field = AV_FIELD_UNKNOWN;
//FIXME replace the crap with get_bits()
while (buf < buf_end) {
uint32_t start_code = -1;
buf= avpriv_find_start_code(buf, buf_end, &start_code);
bytes_left = buf_end - buf;
switch(start_code) {
case PICTURE_START_CODE:
if (bytes_left >= 2) {
s->pict_type = (buf[1] >> 3) & 7;
if (bytes_left >= 4)
vbv_delay = ((buf[1] & 0x07) << 13) | (buf[2] << 5) | (buf[3] >> 3);
}
break;
case SEQ_START_CODE:
if (bytes_left >= 7) {
int frame_rate_index;
pc->width = (buf[0] << 4) | (buf[1] >> 4);
pc->height = ((buf[1] & 0x0f) << 8) | buf[2];
if(!avctx->width || !avctx->height || !avctx->coded_width || !avctx->coded_height){
set_dim_ret = ff_set_dimensions(avctx, pc->width, pc->height);
did_set_size=1;
}
pix_fmt = AV_PIX_FMT_YUV420P;
frame_rate_index = buf[3] & 0xf;
pc->frame_rate = avctx->framerate = ff_mpeg12_frame_rate_tab[frame_rate_index];
bit_rate = (buf[4]<<10) | (buf[5]<<2) | (buf[6]>>6);
avctx->codec_id = AV_CODEC_ID_MPEG1VIDEO;
#if FF_API_TICKS_PER_FRAME
FF_DISABLE_DEPRECATION_WARNINGS
avctx->ticks_per_frame = 1;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
}
break;
case EXT_START_CODE:
if (bytes_left >= 1) {
switch (buf[0] >> 4) { // ext_type
case 0x1: /* sequence extension */
if (bytes_left >= 6) {
int horiz_size_ext = ((buf[1] & 1) << 1) | (buf[2] >> 7);
int vert_size_ext = (buf[2] >> 5) & 3;
int bit_rate_ext = ((buf[2] & 0x1F)<<7) | (buf[3]>>1);
int frame_rate_ext_n = (buf[5] >> 5) & 3;
int frame_rate_ext_d = (buf[5] & 0x1f);
pc->progressive_sequence = buf[1] & (1 << 3);
avctx->has_b_frames= !(buf[5] >> 7);
switch ((buf[1] >> 1) & 3) { // chroma_format
case 1: pix_fmt = AV_PIX_FMT_YUV420P; break;
case 2: pix_fmt = AV_PIX_FMT_YUV422P; break;
case 3: pix_fmt = AV_PIX_FMT_YUV444P; break;
}
pc->width = (pc->width & 0xFFF) | (horiz_size_ext << 12);
pc->height = (pc->height& 0xFFF) | ( vert_size_ext << 12);
bit_rate = (bit_rate&0x3FFFF) | (bit_rate_ext << 18);
if(did_set_size)
set_dim_ret = ff_set_dimensions(avctx, pc->width, pc->height);
avctx->framerate.num = pc->frame_rate.num * (frame_rate_ext_n + 1);
avctx->framerate.den = pc->frame_rate.den * (frame_rate_ext_d + 1);
avctx->codec_id = AV_CODEC_ID_MPEG2VIDEO;
#if FF_API_TICKS_PER_FRAME
FF_DISABLE_DEPRECATION_WARNINGS
avctx->ticks_per_frame = 2;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
}
break;
case 0x8: /* picture coding extension */
if (bytes_left >= 5) {
int top_field_first = buf[3] & (1 << 7);
int repeat_first_field = buf[3] & (1 << 1);
int progressive_frame = buf[4] & (1 << 7);
/* check if we must repeat the frame */
s->repeat_pict = 1;
if (repeat_first_field) {
if (pc->progressive_sequence) {
if (top_field_first)
s->repeat_pict = 5;
else
s->repeat_pict = 3;
} else if (progressive_frame) {
s->repeat_pict = 2;
}
}
if (!pc->progressive_sequence && !progressive_frame) {
if (top_field_first)
s->field_order = AV_FIELD_TT;
else
s->field_order = AV_FIELD_BB;
} else
s->field_order = AV_FIELD_PROGRESSIVE;
s->picture_structure = buf[2] & 3;
if (!nb_pic_ext) {
// remember parity of the first field for the case
// when there are 2 fields in packet
switch (s->picture_structure) {
case AV_PICTURE_STRUCTURE_BOTTOM_FIELD: first_field = AV_FIELD_BB; break;
case AV_PICTURE_STRUCTURE_TOP_FIELD: first_field = AV_FIELD_TT; break;
}
}
nb_pic_ext++;
}
break;
}
}
break;
case -1:
goto the_end;
default:
/* we stop parsing when we encounter a slice. It ensures
that this function takes a negligible amount of time */
if (start_code >= SLICE_MIN_START_CODE &&
start_code <= SLICE_MAX_START_CODE)
goto the_end;
break;
}
}
the_end:
if (set_dim_ret < 0)
av_log(avctx, AV_LOG_ERROR, "Failed to set dimensions\n");
if (avctx->codec_id == AV_CODEC_ID_MPEG2VIDEO && bit_rate && bit_rate != 0x3FFFF) {
avctx->rc_max_rate = 400LL*bit_rate;
}
if (bit_rate &&
((avctx->codec_id == AV_CODEC_ID_MPEG1VIDEO && bit_rate != 0x3FFFF) || vbv_delay != 0xFFFF)) {
avctx->bit_rate = 400LL*bit_rate;
}
if (pix_fmt != AV_PIX_FMT_NONE) {
s->format = pix_fmt;
s->width = pc->width;
s->height = pc->height;
s->coded_width = FFALIGN(pc->width, 16);
s->coded_height = FFALIGN(pc->height, 16);
}
if (avctx->codec_id == AV_CODEC_ID_MPEG1VIDEO || nb_pic_ext > 1) {
s->repeat_pict = 1;
s->picture_structure = AV_PICTURE_STRUCTURE_FRAME;
s->field_order = nb_pic_ext > 1 ? first_field : AV_FIELD_PROGRESSIVE;
}
}
static int mpegvideo_parse(AVCodecParserContext *s,
AVCodecContext *avctx,
const uint8_t **poutbuf, int *poutbuf_size,
const uint8_t *buf, int buf_size)
{
struct MpvParseContext *pc1 = s->priv_data;
ParseContext *pc= &pc1->pc;
int next;
if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
next= buf_size;
}else{
next = mpeg1_find_frame_end(pc, buf, buf_size, s);
if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
*poutbuf = NULL;
*poutbuf_size = 0;
return buf_size;
}
}
/* we have a full frame : we just parse the first few MPEG headers
to have the full timing information. The time take by this
function should be negligible for uncorrupted streams */
mpegvideo_extract_headers(s, avctx, buf, buf_size);
ff_dlog(NULL, "pict_type=%d frame_rate=%0.3f repeat_pict=%d\n",
s->pict_type, av_q2d(avctx->framerate), s->repeat_pict);
*poutbuf = buf;
*poutbuf_size = buf_size;
return next;
}
static int mpegvideo_parse_init(AVCodecParserContext *s)
{
s->pict_type = AV_PICTURE_TYPE_NONE; // first frame might be partial
return 0;
}
const AVCodecParser ff_mpegvideo_parser = {
.codec_ids = { AV_CODEC_ID_MPEG1VIDEO, AV_CODEC_ID_MPEG2VIDEO },
.priv_data_size = sizeof(struct MpvParseContext),
.parser_init = mpegvideo_parse_init,
.parser_parse = mpegvideo_parse,
.parser_close = ff_parse_close,
};
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