path: root/libavcodec/h261dec.c (plain)
blob: 7f2fff8684eb7359b32adb58c080e6331731f365

1	/*
2	* H.261 decoder
3	* Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
4	* Copyright (c) 2004 Maarten Daniels
5	*
6	* This file is part of FFmpeg.
7	*
8	* FFmpeg is free software; you can redistribute it and/or
9	* modify it under the terms of the GNU Lesser General Public
10	* License as published by the Free Software Foundation; either
11	* version 2.1 of the License, or (at your option) any later version.
12	*
13	* FFmpeg is distributed in the hope that it will be useful,
14	* but WITHOUT ANY WARRANTY; without even the implied warranty of
15	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16	* Lesser General Public License for more details.
17	*
18	* You should have received a copy of the GNU Lesser General Public
19	* License along with FFmpeg; if not, write to the Free Software
20	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21	*/
22
23	/**
24	* @file
25	* H.261 decoder.
26	*/
27
28	#include "libavutil/avassert.h"
29	#include "avcodec.h"
30	#include "mpeg_er.h"
31	#include "mpegutils.h"
32	#include "mpegvideo.h"
33	#include "h263.h"
34	#include "h261.h"
35	#include "internal.h"
36
37	#define H261_MBA_VLC_BITS 9
38	#define H261_MTYPE_VLC_BITS 6
39	#define H261_MV_VLC_BITS 7
40	#define H261_CBP_VLC_BITS 9
41	#define TCOEFF_VLC_BITS 9
42	#define MBA_STUFFING 33
43	#define MBA_STARTCODE 34
44
45	static VLC h261_mba_vlc;
46	static VLC h261_mtype_vlc;
47	static VLC h261_mv_vlc;
48	static VLC h261_cbp_vlc;
49
50	static av_cold void h261_decode_init_vlc(H261Context *h)
51	{
52	static int done = 0;
53
54	if (!done) {
55	done = 1;
56	INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,
57	ff_h261_mba_bits, 1, 1,
58	ff_h261_mba_code, 1, 1, 662);
59	INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,
60	ff_h261_mtype_bits, 1, 1,
61	ff_h261_mtype_code, 1, 1, 80);
62	INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,
63	&ff_h261_mv_tab[0][1], 2, 1,
64	&ff_h261_mv_tab[0][0], 2, 1, 144);
65	INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,
66	&ff_h261_cbp_tab[0][1], 2, 1,
67	&ff_h261_cbp_tab[0][0], 2, 1, 512);
68	INIT_VLC_RL(ff_h261_rl_tcoeff, 552);
69	}
70	}
71
72	static av_cold int h261_decode_init(AVCodecContext *avctx)
73	{
74	H261Context *h = avctx->priv_data;
75	MpegEncContext *const s = &h->s;
76
77	// set defaults
78	ff_mpv_decode_defaults(s);
79	ff_mpv_decode_init(s, avctx);
80
81	s->out_format = FMT_H261;
82	s->low_delay = 1;
83	avctx->pix_fmt = AV_PIX_FMT_YUV420P;
84
85	ff_h261_common_init();
86	h261_decode_init_vlc(h);
87
88	h->gob_start_code_skipped = 0;
89
90	return 0;
91	}
92
93	/**
94	* Decode the group of blocks header or slice header.
95	* @return <0 if an error occurred
96	*/
97	static int h261_decode_gob_header(H261Context *h)
98	{
99	unsigned int val;
100	MpegEncContext *const s = &h->s;
101
102	if (!h->gob_start_code_skipped) {
103	/* Check for GOB Start Code */
104	val = show_bits(&s->gb, 15);
105	if (val)
106	return -1;
107
108	/* We have a GBSC */
109	skip_bits(&s->gb, 16);
110	}
111
112	h->gob_start_code_skipped = 0;
113
114	h->gob_number = get_bits(&s->gb, 4); /* GN */
115	s->qscale = get_bits(&s->gb, 5); /* GQUANT */
116
117	/* Check if gob_number is valid */
118	if (s->mb_height == 18) { // CIF
119	if ((h->gob_number <= 0) || (h->gob_number > 12))
120	return -1;
121	} else { // QCIF
122	if ((h->gob_number != 1) && (h->gob_number != 3) &&
123	(h->gob_number != 5))
124	return -1;
125	}
126
127	/* GEI */
128	if (skip_1stop_8data_bits(&s->gb) < 0)
129	return AVERROR_INVALIDDATA;
130
131	if (s->qscale == 0) {
132	av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");
133	if (s->avctx->err_recognition & (AV_EF_BITSTREAM | AV_EF_COMPLIANT))
134	return -1;
135	}
136
137	/* For the first transmitted macroblock in a GOB, MBA is the absolute
138	* address. For subsequent macroblocks, MBA is the difference between
139	* the absolute addresses of the macroblock and the last transmitted
140	* macroblock. */
141	h->current_mba = 0;
142	h->mba_diff = 0;
143
144	return 0;
145	}
146
147	/**
148	* Decode the group of blocks / video packet header.
149	* @return <0 if no resync found
150	*/
151	static int h261_resync(H261Context *h)
152	{
153	MpegEncContext *const s = &h->s;
154	int left, ret;
155
156	if (h->gob_start_code_skipped) {
157	ret = h261_decode_gob_header(h);
158	if (ret >= 0)
159	return 0;
160	} else {
161	if (show_bits(&s->gb, 15) == 0) {
162	ret = h261_decode_gob_header(h);
163	if (ret >= 0)
164	return 0;
165	}
166	// OK, it is not where it is supposed to be ...
167	s->gb = s->last_resync_gb;
168	align_get_bits(&s->gb);
169	left = get_bits_left(&s->gb);
170
171	for (; left > 15 + 1 + 4 + 5; left -= 8) {
172	if (show_bits(&s->gb, 15) == 0) {
173	GetBitContext bak = s->gb;
174
175	ret = h261_decode_gob_header(h);
176	if (ret >= 0)
177	return 0;
178
179	s->gb = bak;
180	}
181	skip_bits(&s->gb, 8);
182	}
183	}
184
185	return -1;
186	}
187
188	/**
189	* Decode skipped macroblocks.
190	* @return 0
191	*/
192	static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2)
193	{
194	MpegEncContext *const s = &h->s;
195	int i;
196
197	s->mb_intra = 0;
198
199	for (i = mba1; i < mba2; i++) {
200	int j, xy;
201
202	s->mb_x = ((h->gob_number - 1) % 2) * 11 + i % 11;
203	s->mb_y = ((h->gob_number - 1) / 2) * 3 + i / 11;
204	xy = s->mb_x + s->mb_y * s->mb_stride;
205	ff_init_block_index(s);
206	ff_update_block_index(s);
207
208	for (j = 0; j < 6; j++)
209	s->block_last_index[j] = -1;
210
211	s->mv_dir = MV_DIR_FORWARD;
212	s->mv_type = MV_TYPE_16X16;
213	s->current_picture.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
214	s->mv[0][0][0] = 0;
215	s->mv[0][0][1] = 0;
216	s->mb_skipped = 1;
217	h->mtype &= ~MB_TYPE_H261_FIL;
218
219	if (s->current_picture.motion_val[0]) {
220	int b_stride = 2*s->mb_width + 1;
221	int b_xy = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
222	s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
223	s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
224	}
225
226	ff_mpv_decode_mb(s, s->block);
227	}
228
229	return 0;
230	}
231
232	static const int mvmap[17] = {
233	0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16
234	};
235
236	static int decode_mv_component(GetBitContext *gb, int v)
237	{
238	int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
239
240	/* check if mv_diff is valid */
241	if (mv_diff < 0)
242	return v;
243
244	mv_diff = mvmap[mv_diff];
245
246	if (mv_diff && !get_bits1(gb))
247	mv_diff = -mv_diff;
248
249	v += mv_diff;
250	if (v <= -16)
251	v += 32;
252	else if (v >= 16)
253	v -= 32;
254
255	return v;
256	}
257
258	/**
259	* Decode a macroblock.
260	* @return <0 if an error occurred
261	*/
262	static int h261_decode_block(H261Context *h, int16_t *block, int n, int coded)
263	{
264	MpegEncContext *const s = &h->s;
265	int level, i, j, run;
266	RLTable *rl = &ff_h261_rl_tcoeff;
267	const uint8_t *scan_table;
268
269	/* For the variable length encoding there are two code tables, one being
270	* used for the first transmitted LEVEL in INTER, INTER + MC and
271	* INTER + MC + FIL blocks, the second for all other LEVELs except the
272	* first one in INTRA blocks which is fixed length coded with 8 bits.
273	* NOTE: The two code tables only differ in one VLC so we handle that
274	* manually. */
275	scan_table = s->intra_scantable.permutated;
276	if (s->mb_intra) {
277	/* DC coef */
278	level = get_bits(&s->gb, 8);
279	// 0 (00000000b) and -128 (10000000b) are FORBIDDEN
280	if ((level & 0x7F) == 0) {
281	av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n",
282	level, s->mb_x, s->mb_y);
283	return -1;
284	}
285	/* The code 1000 0000 is not used, the reconstruction level of 1024
286	* being coded as 1111 1111. */
287	if (level == 255)
288	level = 128;
289	block[0] = level;
290	i = 1;
291	} else if (coded) {
292	// Run Level Code
293	// EOB Not possible for first level when cbp is available (that's why the table is different)
294	// 0 1 1s
295	// * * 0*
296	int check = show_bits(&s->gb, 2);
297	i = 0;
298	if (check & 0x2) {
299	skip_bits(&s->gb, 2);
300	block[0] = (check & 0x1) ? -1 : 1;
301	i = 1;
302	}
303	} else {
304	i = 0;
305	}
306	if (!coded) {
307	s->block_last_index[n] = i - 1;
308	return 0;
309	}
310	{
311	OPEN_READER(re, &s->gb);
312	i--; // offset by -1 to allow direct indexing of scan_table
313	for (;;) {
314	UPDATE_CACHE(re, &s->gb);
315	GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TCOEFF_VLC_BITS, 2, 0);
316	if (run == 66) {
317	if (level) {
318	CLOSE_READER(re, &s->gb);
319	av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",
320	s->mb_x, s->mb_y);
321	return -1;
322	}
323	/* escape */
324	/* The remaining combinations of (run, level) are encoded with a
325	* 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits
326	* level. */
327	run = SHOW_UBITS(re, &s->gb, 6) + 1;
328	SKIP_CACHE(re, &s->gb, 6);
329	level = SHOW_SBITS(re, &s->gb, 8);
330	SKIP_COUNTER(re, &s->gb, 6 + 8);
331	} else if (level == 0) {
332	break;
333	} else {
334	if (SHOW_UBITS(re, &s->gb, 1))
335	level = -level;
336	SKIP_COUNTER(re, &s->gb, 1);
337	}
338	i += run;
339	if (i >= 64) {
340	CLOSE_READER(re, &s->gb);
341	av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",
342	s->mb_x, s->mb_y);
343	return -1;
344	}
345	j = scan_table[i];
346	block[j] = level;
347	}
348	CLOSE_READER(re, &s->gb);
349	}
350	s->block_last_index[n] = i;
351	return 0;
352	}
353
354	static int h261_decode_mb(H261Context *h)
355	{
356	MpegEncContext *const s = &h->s;
357	int i, cbp, xy;
358
359	cbp = 63;
360	// Read mba
361	do {
362	h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,
363	H261_MBA_VLC_BITS, 2);
364
365	/* Check for slice end */
366	/* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */
367	if (h->mba_diff == MBA_STARTCODE) { // start code
368	h->gob_start_code_skipped = 1;
369	return SLICE_END;
370	}
371	} while (h->mba_diff == MBA_STUFFING); // stuffing
372
373	if (h->mba_diff < 0) {
374	if (get_bits_left(&s->gb) <= 7)
375	return SLICE_END;
376
377	av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
378	return SLICE_ERROR;
379	}
380
381	h->mba_diff += 1;
382	h->current_mba += h->mba_diff;
383
384	if (h->current_mba > MBA_STUFFING)
385	return SLICE_ERROR;
386
387	s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);
388	s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);
389	xy = s->mb_x + s->mb_y * s->mb_stride;
390	ff_init_block_index(s);
391	ff_update_block_index(s);
392
393	// Read mtype
394	h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);
395	if (h->mtype < 0) {
396	av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index %d\n",
397	h->mtype);
398	return SLICE_ERROR;
399	}
400	av_assert0(h->mtype < FF_ARRAY_ELEMS(ff_h261_mtype_map));
401	h->mtype = ff_h261_mtype_map[h->mtype];
402
403	// Read mquant
404	if (IS_QUANT(h->mtype))
405	ff_set_qscale(s, get_bits(&s->gb, 5));
406
407	s->mb_intra = IS_INTRA4x4(h->mtype);
408
409	// Read mv
410	if (IS_16X16(h->mtype)) {
411	/* Motion vector data is included for all MC macroblocks. MVD is
412	* obtained from the macroblock vector by subtracting the vector
413	* of the preceding macroblock. For this calculation the vector
414	* of the preceding macroblock is regarded as zero in the
415	* following three situations:
416	* 1) evaluating MVD for macroblocks 1, 12 and 23;
417	* 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
418	* 3) MTYPE of the previous macroblock was not MC. */
419	if ((h->current_mba == 1) || (h->current_mba == 12) ||
420	(h->current_mba == 23) || (h->mba_diff != 1)) {
421	h->current_mv_x = 0;
422	h->current_mv_y = 0;
423	}
424
425	h->current_mv_x = decode_mv_component(&s->gb, h->current_mv_x);
426	h->current_mv_y = decode_mv_component(&s->gb, h->current_mv_y);
427	} else {
428	h->current_mv_x = 0;
429	h->current_mv_y = 0;
430	}
431
432	// Read cbp
433	if (HAS_CBP(h->mtype))
434	cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
435
436	if (s->mb_intra) {
437	s->current_picture.mb_type[xy] = MB_TYPE_INTRA;
438	goto intra;
439	}
440
441	//set motion vectors
442	s->mv_dir = MV_DIR_FORWARD;
443	s->mv_type = MV_TYPE_16X16;
444	s->current_picture.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;
445	s->mv[0][0][0] = h->current_mv_x * 2; // gets divided by 2 in motion compensation
446	s->mv[0][0][1] = h->current_mv_y * 2;
447
448	if (s->current_picture.motion_val[0]) {
449	int b_stride = 2*s->mb_width + 1;
450	int b_xy = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
451	s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
452	s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
453	}
454
455	intra:
456	/* decode each block */
457	if (s->mb_intra || HAS_CBP(h->mtype)) {
458	s->bdsp.clear_blocks(s->block[0]);
459	for (i = 0; i < 6; i++) {
460	if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)
461	return SLICE_ERROR;
462	cbp += cbp;
463	}
464	} else {
465	for (i = 0; i < 6; i++)
466	s->block_last_index[i] = -1;
467	}
468
469	ff_mpv_decode_mb(s, s->block);
470
471	return SLICE_OK;
472	}
473
474	/**
475	* Decode the H.261 picture header.
476	* @return <0 if no startcode found
477	*/
478	static int h261_decode_picture_header(H261Context *h)
479	{
480	MpegEncContext *const s = &h->s;
481	int format, i;
482	uint32_t startcode = 0;
483
484	for (i = get_bits_left(&s->gb); i > 24; i -= 1) {
485	startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
486
487	if (startcode == 0x10)
488	break;
489	}
490
491	if (startcode != 0x10) {
492	av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
493	return -1;
494	}
495
496	/* temporal reference */
497	i = get_bits(&s->gb, 5); /* picture timestamp */
498	if (i < (s->picture_number & 31))
499	i += 32;
500	s->picture_number = (s->picture_number & ~31) + i;
501
502	s->avctx->framerate = (AVRational) { 30000, 1001 };
503
504	/* PTYPE starts here */
505	skip_bits1(&s->gb); /* split screen off */
506	skip_bits1(&s->gb); /* camera off */
507	skip_bits1(&s->gb); /* freeze picture release off */
508
509	format = get_bits1(&s->gb);
510
511	// only 2 formats possible
512	if (format == 0) { // QCIF
513	s->width = 176;
514	s->height = 144;
515	s->mb_width = 11;
516	s->mb_height = 9;
517	} else { // CIF
518	s->width = 352;
519	s->height = 288;
520	s->mb_width = 22;
521	s->mb_height = 18;
522	}
523
524	s->mb_num = s->mb_width * s->mb_height;
525
526	skip_bits1(&s->gb); /* still image mode off */
527	skip_bits1(&s->gb); /* Reserved */
528
529	/* PEI */
530	if (skip_1stop_8data_bits(&s->gb) < 0)
531	return AVERROR_INVALIDDATA;
532
533	/* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
534	* frame, the codec crashes if it does not contain all I-blocks
535	* (e.g. when a packet is lost). */
536	s->pict_type = AV_PICTURE_TYPE_P;
537
538	h->gob_number = 0;
539	return 0;
540	}
541
542	static int h261_decode_gob(H261Context *h)
543	{
544	MpegEncContext *const s = &h->s;
545
546	ff_set_qscale(s, s->qscale);
547
548	/* decode mb's */
549	while (h->current_mba <= MBA_STUFFING) {
550	int ret;
551	/* DCT & quantize */
552	ret = h261_decode_mb(h);
553	if (ret < 0) {
554	if (ret == SLICE_END) {
555	h261_decode_mb_skipped(h, h->current_mba, 33);
556	return 0;
557	}
558	av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",
559	s->mb_x + s->mb_y * s->mb_stride);
560	return -1;
561	}
562
563	h261_decode_mb_skipped(h,
564	h->current_mba - h->mba_diff,
565	h->current_mba - 1);
566	}
567
568	return -1;
569	}
570
571	/**
572	* returns the number of bytes consumed for building the current frame
573	*/
574	static int get_consumed_bytes(MpegEncContext *s, int buf_size)
575	{
576	int pos = get_bits_count(&s->gb) >> 3;
577	if (pos == 0)
578	pos = 1; // avoid infinite loops (i doubt that is needed but ...)
579	if (pos + 10 > buf_size)
580	pos = buf_size; // oops ;)
581
582	return pos;
583	}
584
585	static int h261_decode_frame(AVCodecContext *avctx, void *data,
586	int *got_frame, AVPacket *avpkt)
587	{
588	const uint8_t *buf = avpkt->data;
589	int buf_size = avpkt->size;
590	H261Context *h = avctx->priv_data;
591	MpegEncContext *s = &h->s;
592	int ret;
593	AVFrame *pict = data;
594
595	ff_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
596	ff_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
597
598	h->gob_start_code_skipped = 0;
599
600	retry:
601	init_get_bits(&s->gb, buf, buf_size * 8);
602
603	if (!s->context_initialized)
604	// we need the IDCT permutation for reading a custom matrix
605	ff_mpv_idct_init(s);
606
607	ret = h261_decode_picture_header(h);
608
609	/* skip if the header was thrashed */
610	if (ret < 0) {
611	av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
612	return -1;
613	}
614
615	if (s->width != avctx->coded_width || s->height != avctx->coded_height) {
616	ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat
617	s->parse_context.buffer = 0;
618	ff_mpv_common_end(s);
619	s->parse_context = pc;
620	}
621
622	if (!s->context_initialized) {
623	if ((ret = ff_mpv_common_init(s)) < 0)
624	return ret;
625
626	ret = ff_set_dimensions(avctx, s->width, s->height);
627	if (ret < 0)
628	return ret;
629
630	goto retry;
631	}
632
633	// for skipping the frame
634	s->current_picture.f->pict_type = s->pict_type;
635	s->current_picture.f->key_frame = s->pict_type == AV_PICTURE_TYPE_I;
636
637	if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||
638	(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type != AV_PICTURE_TYPE_I) ||
639	avctx->skip_frame >= AVDISCARD_ALL)
640	return get_consumed_bytes(s, buf_size);
641
642	if (ff_mpv_frame_start(s, avctx) < 0)
643	return -1;
644
645	ff_mpeg_er_frame_start(s);
646
647	/* decode each macroblock */
648	s->mb_x = 0;
649	s->mb_y = 0;
650
651	while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {
652	if (h261_resync(h) < 0)
653	break;
654	h261_decode_gob(h);
655	}
656	ff_mpv_frame_end(s);
657
658	av_assert0(s->current_picture.f->pict_type == s->current_picture_ptr->f->pict_type);
659	av_assert0(s->current_picture.f->pict_type == s->pict_type);
660
661	if ((ret = av_frame_ref(pict, s->current_picture_ptr->f)) < 0)
662	return ret;
663	ff_print_debug_info(s, s->current_picture_ptr, pict);
664
665	*got_frame = 1;
666
667	return get_consumed_bytes(s, buf_size);
668	}
669
670	static av_cold int h261_decode_end(AVCodecContext *avctx)
671	{
672	H261Context *h = avctx->priv_data;
673	MpegEncContext *s = &h->s;
674
675	ff_mpv_common_end(s);
676	return 0;
677	}
678
679	AVCodec ff_h261_decoder = {
680	.name = "h261",
681	.long_name = NULL_IF_CONFIG_SMALL("H.261"),
682	.type = AVMEDIA_TYPE_VIDEO,
683	.id = AV_CODEC_ID_H261,
684	.priv_data_size = sizeof(H261Context),
685	.init = h261_decode_init,
686	.close = h261_decode_end,
687	.decode = h261_decode_frame,
688	.capabilities = AV_CODEC_CAP_DR1,
689	.max_lowres = 3,
690	};
691