libavcodec/pngenc.c - third_party/ffmpeg - Git at Google

 /*
  * PNG image format
  * Copyright (c) 2003 Fabrice Bellard
  *
  * 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 "avcodec.h"
 #include "internal.h"
 #include "bytestream.h"
 #include "dsputil.h"
 #include "png.h"

 #include "libavutil/avassert.h"
 #include "libavutil/opt.h"

 #include <zlib.h>

 #define IOBUF_SIZE 4096

 typedef struct PNGEncContext {
     AVClass *class;
     DSPContext dsp;

     uint8_t *bytestream;
     uint8_t *bytestream_start;
     uint8_t *bytestream_end;

     int filter_type;

     z_stream zstream;
     uint8_t buf[IOBUF_SIZE];
     int dpi;                     ///< Physical pixel density, in dots per inch, if set
     int dpm;                     ///< Physical pixel density, in dots per meter, if set
 } PNGEncContext;

 static void png_get_interlaced_row(uint8_t *dst, int row_size,
                                    int bits_per_pixel, int pass,
                                    const uint8_t *src, int width)
 {
     int x, mask, dst_x, j, b, bpp;
     uint8_t *d;
     const uint8_t *s;
     static const int masks[] = {0x80, 0x08, 0x88, 0x22, 0xaa, 0x55, 0xff};

     mask = masks[pass];
     switch(bits_per_pixel) {
     case 1:
         memset(dst, 0, row_size);
         dst_x = 0;
         for(x = 0; x < width; x++) {
             j = (x & 7);
             if ((mask << j) & 0x80) {
                 b = (src[x >> 3] >> (7 - j)) & 1;
                 dst[dst_x >> 3] |= b << (7 - (dst_x & 7));
                 dst_x++;
             }
         }
         break;
     default:
         bpp = bits_per_pixel >> 3;
         d = dst;
         s = src;
         for(x = 0; x < width; x++) {
             j = x & 7;
             if ((mask << j) & 0x80) {
                 memcpy(d, s, bpp);
                 d += bpp;
             }
             s += bpp;
         }
         break;
     }
 }

 static void sub_png_paeth_prediction(uint8_t *dst, uint8_t *src, uint8_t *top, int w, int bpp)
 {
     int i;
     for(i = 0; i < w; i++) {
         int a, b, c, p, pa, pb, pc;

         a = src[i - bpp];
         b = top[i];
         c = top[i - bpp];

         p = b - c;
         pc = a - c;

         pa = abs(p);
         pb = abs(pc);
         pc = abs(p + pc);

         if (pa <= pb && pa <= pc)
             p = a;
         else if (pb <= pc)
             p = b;
         else
             p = c;
         dst[i] = src[i] - p;
     }
 }

 static void sub_left_prediction(DSPContext *dsp, uint8_t *dst, const uint8_t *src, int bpp, int size)
 {
     const uint8_t *src1 = src + bpp;
     const uint8_t *src2 = src;
     int x, unaligned_w;

     memcpy(dst, src, bpp);
     dst += bpp;
     size -= bpp;
     unaligned_w = FFMIN(32 - bpp, size);
     for (x = 0; x < unaligned_w; x++)
         *dst++ = *src1++ - *src2++;
     size -= unaligned_w;
     dsp->diff_bytes(dst, src1, src2, size);
 }

 static void png_filter_row(DSPContext *dsp, uint8_t *dst, int filter_type,
                            uint8_t *src, uint8_t *top, int size, int bpp)
 {
     int i;

     switch(filter_type) {
     case PNG_FILTER_VALUE_NONE:
         memcpy(dst, src, size);
         break;
     case PNG_FILTER_VALUE_SUB:
         sub_left_prediction(dsp, dst, src, bpp, size);
         break;
     case PNG_FILTER_VALUE_UP:
         dsp->diff_bytes(dst, src, top, size);
         break;
     case PNG_FILTER_VALUE_AVG:
         for(i = 0; i < bpp; i++)
             dst[i] = src[i] - (top[i] >> 1);
         for(; i < size; i++)
             dst[i] = src[i] - ((src[i-bpp] + top[i]) >> 1);
         break;
     case PNG_FILTER_VALUE_PAETH:
         for(i = 0; i < bpp; i++)
             dst[i] = src[i] - top[i];
         sub_png_paeth_prediction(dst+i, src+i, top+i, size-i, bpp);
         break;
     }
 }

 static uint8_t *png_choose_filter(PNGEncContext *s, uint8_t *dst,
                                   uint8_t *src, uint8_t *top, int size, int bpp)
 {
     int pred = s->filter_type;
     av_assert0(bpp || !pred);
     if(!top && pred)
         pred = PNG_FILTER_VALUE_SUB;
     if(pred == PNG_FILTER_VALUE_MIXED) {
         int i;
         int cost, bcost = INT_MAX;
         uint8_t *buf1 = dst, *buf2 = dst + size + 16;
         for(pred=0; pred<5; pred++) {
             png_filter_row(&s->dsp, buf1+1, pred, src, top, size, bpp);
             buf1[0] = pred;
             cost = 0;
             for(i=0; i<=size; i++)
                 cost += abs((int8_t)buf1[i]);
             if(cost < bcost) {
                 bcost = cost;
                 FFSWAP(uint8_t*, buf1, buf2);
             }
         }
         return buf2;
     } else {
         png_filter_row(&s->dsp, dst+1, pred, src, top, size, bpp);
         dst[0] = pred;
         return dst;
     }
 }

 static void png_write_chunk(uint8_t **f, uint32_t tag,
                             const uint8_t *buf, int length)
 {
     uint32_t crc;
     uint8_t tagbuf[4];

     bytestream_put_be32(f, length);
     crc = crc32(0, Z_NULL, 0);
     AV_WL32(tagbuf, tag);
     crc = crc32(crc, tagbuf, 4);
     bytestream_put_be32(f, av_bswap32(tag));
     if (length > 0) {
         crc = crc32(crc, buf, length);
         memcpy(*f, buf, length);
         *f += length;
     }
     bytestream_put_be32(f, crc);
 }

 /* XXX: do filtering */
 static int png_write_row(PNGEncContext *s, const uint8_t *data, int size)
 {
     int ret;

     s->zstream.avail_in = size;
     s->zstream.next_in = (uint8_t *)data;
     while (s->zstream.avail_in > 0) {
         ret = deflate(&s->zstream, Z_NO_FLUSH);
         if (ret != Z_OK)
             return -1;
         if (s->zstream.avail_out == 0) {
             if(s->bytestream_end - s->bytestream > IOBUF_SIZE + 100)
                 png_write_chunk(&s->bytestream, MKTAG('I', 'D', 'A', 'T'), s->buf, IOBUF_SIZE);
             s->zstream.avail_out = IOBUF_SIZE;
             s->zstream.next_out = s->buf;
         }
     }
     return 0;
 }

 static int encode_frame(AVCodecContext *avctx, AVPacket *pkt,
                         const AVFrame *pict, int *got_packet)
 {
     PNGEncContext *s = avctx->priv_data;
     const AVFrame * const p = pict;
     int bit_depth, color_type, y, len, row_size, ret, is_progressive;
     int bits_per_pixel, pass_row_size, enc_row_size;
     int64_t max_packet_size;
     int compression_level;
     uint8_t *ptr, *top;
     uint8_t *crow_base = NULL, *crow_buf, *crow;
     uint8_t *progressive_buf = NULL;
     uint8_t *top_buf = NULL;

     is_progressive = !!(avctx->flags & CODEC_FLAG_INTERLACED_DCT);
     switch(avctx->pix_fmt) {
     case AV_PIX_FMT_RGBA64BE:
         bit_depth = 16;
         color_type = PNG_COLOR_TYPE_RGB_ALPHA;
         break;
     case AV_PIX_FMT_RGB48BE:
         bit_depth = 16;
         color_type = PNG_COLOR_TYPE_RGB;
         break;
     case AV_PIX_FMT_RGBA:
         bit_depth = 8;
         color_type = PNG_COLOR_TYPE_RGB_ALPHA;
         break;
     case AV_PIX_FMT_RGB24:
         bit_depth = 8;
         color_type = PNG_COLOR_TYPE_RGB;
         break;
     case AV_PIX_FMT_GRAY16BE:
         bit_depth = 16;
         color_type = PNG_COLOR_TYPE_GRAY;
         break;
     case AV_PIX_FMT_GRAY8:
         bit_depth = 8;
         color_type = PNG_COLOR_TYPE_GRAY;
         break;
     case AV_PIX_FMT_GRAY8A:
         bit_depth = 8;
         color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
         break;
     case AV_PIX_FMT_MONOBLACK:
         bit_depth = 1;
         color_type = PNG_COLOR_TYPE_GRAY;
         break;
     case AV_PIX_FMT_PAL8:
         bit_depth = 8;
         color_type = PNG_COLOR_TYPE_PALETTE;
         break;
     default:
         return -1;
     }
     bits_per_pixel = ff_png_get_nb_channels(color_type) * bit_depth;
     row_size = (avctx->width * bits_per_pixel + 7) >> 3;

     s->zstream.zalloc = ff_png_zalloc;
     s->zstream.zfree = ff_png_zfree;
     s->zstream.opaque = NULL;
     compression_level = avctx->compression_level == FF_COMPRESSION_DEFAULT ?
                             Z_DEFAULT_COMPRESSION :
                             av_clip(avctx->compression_level, 0, 9);
     ret = deflateInit2(&s->zstream, compression_level,
                        Z_DEFLATED, 15, 8, Z_DEFAULT_STRATEGY);
     if (ret != Z_OK)
         return -1;

     enc_row_size    = deflateBound(&s->zstream, row_size);
     max_packet_size = avctx->height * (int64_t)(enc_row_size +
                                        ((enc_row_size + IOBUF_SIZE - 1) / IOBUF_SIZE) * 12)
                       + FF_MIN_BUFFER_SIZE;
     if (max_packet_size > INT_MAX)
         return AVERROR(ENOMEM);
     if ((ret = ff_alloc_packet2(avctx, pkt, max_packet_size)) < 0)
         return ret;

     s->bytestream_start =
     s->bytestream       = pkt->data;
     s->bytestream_end   = pkt->data + pkt->size;

     crow_base = av_malloc((row_size + 32) << (s->filter_type == PNG_FILTER_VALUE_MIXED));
     if (!crow_base)
         goto fail;
     crow_buf = crow_base + 15; // pixel data should be aligned, but there's a control byte before it
     if (is_progressive) {
         progressive_buf = av_malloc(row_size + 1);
         if (!progressive_buf)
             goto fail;
     }
     if (is_progressive) {
         top_buf = av_malloc(row_size + 1);
         if (!top_buf)
             goto fail;
     }

     /* write png header */
     AV_WB64(s->bytestream, PNGSIG);
     s->bytestream += 8;

     AV_WB32(s->buf, avctx->width);
     AV_WB32(s->buf + 4, avctx->height);
     s->buf[8] = bit_depth;
     s->buf[9] = color_type;
     s->buf[10] = 0; /* compression type */
     s->buf[11] = 0; /* filter type */
     s->buf[12] = is_progressive; /* interlace type */

     png_write_chunk(&s->bytestream, MKTAG('I', 'H', 'D', 'R'), s->buf, 13);

     if (s->dpm) {
       AV_WB32(s->buf, s->dpm);
       AV_WB32(s->buf + 4, s->dpm);
       s->buf[8] = 1; /* unit specifier is meter */
     } else {
       AV_WB32(s->buf, avctx->sample_aspect_ratio.num);
       AV_WB32(s->buf + 4, avctx->sample_aspect_ratio.den);
       s->buf[8] = 0; /* unit specifier is unknown */
     }
     png_write_chunk(&s->bytestream, MKTAG('p', 'H', 'Y', 's'), s->buf, 9);

     /* put the palette if needed */
     if (color_type == PNG_COLOR_TYPE_PALETTE) {
         int has_alpha, alpha, i;
         unsigned int v;
         uint32_t *palette;
         uint8_t *alpha_ptr;

         palette = (uint32_t *)p->data[1];
         ptr = s->buf;
         alpha_ptr = s->buf + 256 * 3;
         has_alpha = 0;
         for(i = 0; i < 256; i++) {
             v = palette[i];
             alpha = v >> 24;
             if (alpha != 0xff)
                 has_alpha = 1;
             *alpha_ptr++ = alpha;
             bytestream_put_be24(&ptr, v);
         }
         png_write_chunk(&s->bytestream, MKTAG('P', 'L', 'T', 'E'), s->buf, 256 * 3);
         if (has_alpha) {
             png_write_chunk(&s->bytestream, MKTAG('t', 'R', 'N', 'S'), s->buf + 256 * 3, 256);
         }
     }

     /* now put each row */
     s->zstream.avail_out = IOBUF_SIZE;
     s->zstream.next_out = s->buf;
     if (is_progressive) {
         int pass;

         for(pass = 0; pass < NB_PASSES; pass++) {
             /* NOTE: a pass is completely omitted if no pixels would be
                output */
             pass_row_size = ff_png_pass_row_size(pass, bits_per_pixel, avctx->width);
             if (pass_row_size > 0) {
                 top = NULL;
                 for(y = 0; y < avctx->height; y++) {
                     if ((ff_png_pass_ymask[pass] << (y & 7)) & 0x80) {
                         ptr = p->data[0] + y * p->linesize[0];
                         FFSWAP(uint8_t*, progressive_buf, top_buf);
                         png_get_interlaced_row(progressive_buf, pass_row_size,
                                                bits_per_pixel, pass,
                                                ptr, avctx->width);
                         crow = png_choose_filter(s, crow_buf, progressive_buf, top, pass_row_size, bits_per_pixel>>3);
                         png_write_row(s, crow, pass_row_size + 1);
                         top = progressive_buf;
                     }
                 }
             }
         }
     } else {
         top = NULL;
         for(y = 0; y < avctx->height; y++) {
             ptr = p->data[0] + y * p->linesize[0];
             crow = png_choose_filter(s, crow_buf, ptr, top, row_size, bits_per_pixel>>3);
             png_write_row(s, crow, row_size + 1);
             top = ptr;
         }
     }
     /* compress last bytes */
     for(;;) {
         ret = deflate(&s->zstream, Z_FINISH);
         if (ret == Z_OK || ret == Z_STREAM_END) {
             len = IOBUF_SIZE - s->zstream.avail_out;
             if (len > 0 && s->bytestream_end - s->bytestream > len + 100) {
                 png_write_chunk(&s->bytestream, MKTAG('I', 'D', 'A', 'T'), s->buf, len);
             }
             s->zstream.avail_out = IOBUF_SIZE;
             s->zstream.next_out = s->buf;
             if (ret == Z_STREAM_END)
                 break;
         } else {
             goto fail;
         }
     }
     png_write_chunk(&s->bytestream, MKTAG('I', 'E', 'N', 'D'), NULL, 0);

     pkt->size   = s->bytestream - s->bytestream_start;
     pkt->flags |= AV_PKT_FLAG_KEY;
     *got_packet = 1;
     ret         = 0;

  the_end:
     av_free(crow_base);
     av_free(progressive_buf);
     av_free(top_buf);
     deflateEnd(&s->zstream);
     return ret;
  fail:
     ret = -1;
     goto the_end;
 }

 static av_cold int png_enc_init(AVCodecContext *avctx){
     PNGEncContext *s = avctx->priv_data;

     switch(avctx->pix_fmt) {
     case AV_PIX_FMT_RGBA:
         avctx->bits_per_coded_sample = 32;
         break;
     case AV_PIX_FMT_RGB24:
         avctx->bits_per_coded_sample = 24;
         break;
     case AV_PIX_FMT_GRAY8:
         avctx->bits_per_coded_sample = 0x28;
         break;
     case AV_PIX_FMT_MONOBLACK:
         avctx->bits_per_coded_sample = 1;
         break;
     case AV_PIX_FMT_PAL8:
         avctx->bits_per_coded_sample = 8;
     }

     avctx->coded_frame = av_frame_alloc();
     if (!avctx->coded_frame)
         return AVERROR(ENOMEM);

     avctx->coded_frame->pict_type = AV_PICTURE_TYPE_I;
     avctx->coded_frame->key_frame = 1;

     ff_dsputil_init(&s->dsp, avctx);

     s->filter_type = av_clip(avctx->prediction_method, PNG_FILTER_VALUE_NONE, PNG_FILTER_VALUE_MIXED);
     if(avctx->pix_fmt == AV_PIX_FMT_MONOBLACK)
         s->filter_type = PNG_FILTER_VALUE_NONE;

     if (s->dpi && s->dpm) {
       av_log(avctx, AV_LOG_ERROR, "Only one of 'dpi' or 'dpm' options should be set\n");
       return AVERROR(EINVAL);
     } else if (s->dpi) {
       s->dpm = s->dpi * 10000 / 254;
     }

     return 0;
 }

 static av_cold int png_enc_close(AVCodecContext *avctx)
 {
     av_frame_free(&avctx->coded_frame);
     return 0;
 }

 #define OFFSET(x) offsetof(PNGEncContext, x)
 #define VE AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
 static const AVOption options[] = {
     {"dpi", "Set image resolution (in dots per inch)",  OFFSET(dpi), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 0x10000, VE},
     {"dpm", "Set image resolution (in dots per meter)", OFFSET(dpm), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 0x10000, VE},
     { NULL }
 };

 static const AVClass pngenc_class = {
     .class_name = "PNG encoder",
     .item_name  = av_default_item_name,
     .option     = options,
     .version    = LIBAVUTIL_VERSION_INT,
 };

 AVCodec ff_png_encoder = {
     .name           = "png",
     .long_name      = NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
     .type           = AVMEDIA_TYPE_VIDEO,
     .id             = AV_CODEC_ID_PNG,
     .priv_data_size = sizeof(PNGEncContext),
     .init           = png_enc_init,
     .close          = png_enc_close,
     .encode2        = encode_frame,
     .capabilities   = CODEC_CAP_FRAME_THREADS | CODEC_CAP_INTRA_ONLY,
     .pix_fmts       = (const enum AVPixelFormat[]){
         AV_PIX_FMT_RGB24, AV_PIX_FMT_RGBA,
         AV_PIX_FMT_RGB48BE, AV_PIX_FMT_RGBA64BE,
         AV_PIX_FMT_PAL8,
         AV_PIX_FMT_GRAY8, AV_PIX_FMT_GRAY8A,
         AV_PIX_FMT_GRAY16BE,
         AV_PIX_FMT_MONOBLACK, AV_PIX_FMT_NONE
     },
     .priv_class     = &pngenc_class,
 };
	/*
	* PNG image format
	* Copyright (c) 2003 Fabrice Bellard
	*
	* 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 "avcodec.h"
	#include "internal.h"
	#include "bytestream.h"
	#include "dsputil.h"
	#include "png.h"

	#include "libavutil/avassert.h"
	#include "libavutil/opt.h"

	#include <zlib.h>

	#define IOBUF_SIZE 4096

	typedef struct PNGEncContext {
	AVClass *class;
	DSPContext dsp;

	uint8_t *bytestream;
	uint8_t *bytestream_start;
	uint8_t *bytestream_end;

	int filter_type;

	z_stream zstream;
	uint8_t buf[IOBUF_SIZE];
	int dpi; ///< Physical pixel density, in dots per inch, if set
	int dpm; ///< Physical pixel density, in dots per meter, if set
	} PNGEncContext;

	static void png_get_interlaced_row(uint8_t *dst, int row_size,
	int bits_per_pixel, int pass,
	const uint8_t *src, int width)
	{
	int x, mask, dst_x, j, b, bpp;
	uint8_t *d;
	const uint8_t *s;
	static const int masks[] = {0x80, 0x08, 0x88, 0x22, 0xaa, 0x55, 0xff};

	mask = masks[pass];
	switch(bits_per_pixel) {
	case 1:
	memset(dst, 0, row_size);
	dst_x = 0;
	for(x = 0; x < width; x++) {
	j = (x & 7);
	if ((mask << j) & 0x80) {
	b = (src[x >> 3] >> (7 - j)) & 1;
	dst[dst_x >> 3] \|= b << (7 - (dst_x & 7));
	dst_x++;
	}
	}
	break;
	default:
	bpp = bits_per_pixel >> 3;
	d = dst;
	s = src;
	for(x = 0; x < width; x++) {
	j = x & 7;
	if ((mask << j) & 0x80) {
	memcpy(d, s, bpp);
	d += bpp;
	}
	s += bpp;
	}
	break;
	}
	}

	static void sub_png_paeth_prediction(uint8_t dst, uint8_t src, uint8_t *top, int w, int bpp)
	{
	int i;
	for(i = 0; i < w; i++) {
	int a, b, c, p, pa, pb, pc;

	a = src[i - bpp];
	b = top[i];
	c = top[i - bpp];

	p = b - c;
	pc = a - c;

	pa = abs(p);
	pb = abs(pc);
	pc = abs(p + pc);

	if (pa <= pb && pa <= pc)
	p = a;
	else if (pb <= pc)
	p = b;
	else
	p = c;
	dst[i] = src[i] - p;
	}
	}

	static void sub_left_prediction(DSPContext dsp, uint8_t dst, const uint8_t *src, int bpp, int size)
	{
	const uint8_t *src1 = src + bpp;
	const uint8_t *src2 = src;
	int x, unaligned_w;

	memcpy(dst, src, bpp);
	dst += bpp;
	size -= bpp;
	unaligned_w = FFMIN(32 - bpp, size);
	for (x = 0; x < unaligned_w; x++)
	dst++ = src1++ - *src2++;
	size -= unaligned_w;
	dsp->diff_bytes(dst, src1, src2, size);
	}

	static void png_filter_row(DSPContext dsp, uint8_t dst, int filter_type,
	uint8_t src, uint8_t top, int size, int bpp)
	{
	int i;

	switch(filter_type) {
	case PNG_FILTER_VALUE_NONE:
	memcpy(dst, src, size);
	break;
	case PNG_FILTER_VALUE_SUB:
	sub_left_prediction(dsp, dst, src, bpp, size);
	break;
	case PNG_FILTER_VALUE_UP:
	dsp->diff_bytes(dst, src, top, size);
	break;
	case PNG_FILTER_VALUE_AVG:
	for(i = 0; i < bpp; i++)
	dst[i] = src[i] - (top[i] >> 1);
	for(; i < size; i++)
	dst[i] = src[i] - ((src[i-bpp] + top[i]) >> 1);
	break;
	case PNG_FILTER_VALUE_PAETH:
	for(i = 0; i < bpp; i++)
	dst[i] = src[i] - top[i];
	sub_png_paeth_prediction(dst+i, src+i, top+i, size-i, bpp);
	break;
	}
	}

	static uint8_t png_choose_filter(PNGEncContext s, uint8_t *dst,
	uint8_t src, uint8_t top, int size, int bpp)
	{
	int pred = s->filter_type;
	av_assert0(bpp \|\| !pred);
	if(!top && pred)
	pred = PNG_FILTER_VALUE_SUB;
	if(pred == PNG_FILTER_VALUE_MIXED) {
	int i;
	int cost, bcost = INT_MAX;
	uint8_t buf1 = dst, buf2 = dst + size + 16;
	for(pred=0; pred<5; pred++) {
	png_filter_row(&s->dsp, buf1+1, pred, src, top, size, bpp);
	buf1[0] = pred;
	cost = 0;
	for(i=0; i<=size; i++)
	cost += abs((int8_t)buf1[i]);
	if(cost < bcost) {
	bcost = cost;
	FFSWAP(uint8_t*, buf1, buf2);
	}
	}
	return buf2;
	} else {
	png_filter_row(&s->dsp, dst+1, pred, src, top, size, bpp);
	dst[0] = pred;
	return dst;
	}
	}

	static void png_write_chunk(uint8_t **f, uint32_t tag,
	const uint8_t *buf, int length)
	{
	uint32_t crc;
	uint8_t tagbuf[4];

	bytestream_put_be32(f, length);
	crc = crc32(0, Z_NULL, 0);
	AV_WL32(tagbuf, tag);
	crc = crc32(crc, tagbuf, 4);
	bytestream_put_be32(f, av_bswap32(tag));
	if (length > 0) {
	crc = crc32(crc, buf, length);
	memcpy(*f, buf, length);
	*f += length;
	}
	bytestream_put_be32(f, crc);
	}

	/* XXX: do filtering */
	static int png_write_row(PNGEncContext s, const uint8_t data, int size)
	{
	int ret;

	s->zstream.avail_in = size;
	s->zstream.next_in = (uint8_t *)data;
	while (s->zstream.avail_in > 0) {
	ret = deflate(&s->zstream, Z_NO_FLUSH);
	if (ret != Z_OK)
	return -1;
	if (s->zstream.avail_out == 0) {
	if(s->bytestream_end - s->bytestream > IOBUF_SIZE + 100)
	png_write_chunk(&s->bytestream, MKTAG('I', 'D', 'A', 'T'), s->buf, IOBUF_SIZE);
	s->zstream.avail_out = IOBUF_SIZE;
	s->zstream.next_out = s->buf;
	}
	}
	return 0;
	}

	static int encode_frame(AVCodecContext avctx, AVPacket pkt,
	const AVFrame pict, int got_packet)
	{
	PNGEncContext *s = avctx->priv_data;
	const AVFrame * const p = pict;
	int bit_depth, color_type, y, len, row_size, ret, is_progressive;
	int bits_per_pixel, pass_row_size, enc_row_size;
	int64_t max_packet_size;
	int compression_level;
	uint8_t ptr, top;
	uint8_t crow_base = NULL, crow_buf, *crow;
	uint8_t *progressive_buf = NULL;
	uint8_t *top_buf = NULL;

	is_progressive = !!(avctx->flags & CODEC_FLAG_INTERLACED_DCT);
	switch(avctx->pix_fmt) {
	case AV_PIX_FMT_RGBA64BE:
	bit_depth = 16;
	color_type = PNG_COLOR_TYPE_RGB_ALPHA;
	break;
	case AV_PIX_FMT_RGB48BE:
	bit_depth = 16;
	color_type = PNG_COLOR_TYPE_RGB;
	break;
	case AV_PIX_FMT_RGBA:
	bit_depth = 8;
	color_type = PNG_COLOR_TYPE_RGB_ALPHA;
	break;
	case AV_PIX_FMT_RGB24:
	bit_depth = 8;
	color_type = PNG_COLOR_TYPE_RGB;
	break;
	case AV_PIX_FMT_GRAY16BE:
	bit_depth = 16;
	color_type = PNG_COLOR_TYPE_GRAY;
	break;
	case AV_PIX_FMT_GRAY8:
	bit_depth = 8;
	color_type = PNG_COLOR_TYPE_GRAY;
	break;
	case AV_PIX_FMT_GRAY8A:
	bit_depth = 8;
	color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
	break;
	case AV_PIX_FMT_MONOBLACK:
	bit_depth = 1;
	color_type = PNG_COLOR_TYPE_GRAY;
	break;
	case AV_PIX_FMT_PAL8:
	bit_depth = 8;
	color_type = PNG_COLOR_TYPE_PALETTE;
	break;
	default:
	return -1;
	}
	bits_per_pixel = ff_png_get_nb_channels(color_type) * bit_depth;
	row_size = (avctx->width * bits_per_pixel + 7) >> 3;

	s->zstream.zalloc = ff_png_zalloc;
	s->zstream.zfree = ff_png_zfree;
	s->zstream.opaque = NULL;
	compression_level = avctx->compression_level == FF_COMPRESSION_DEFAULT ?
	Z_DEFAULT_COMPRESSION :
	av_clip(avctx->compression_level, 0, 9);
	ret = deflateInit2(&s->zstream, compression_level,
	Z_DEFLATED, 15, 8, Z_DEFAULT_STRATEGY);
	if (ret != Z_OK)
	return -1;

	enc_row_size = deflateBound(&s->zstream, row_size);
	max_packet_size = avctx->height * (int64_t)(enc_row_size +
	((enc_row_size + IOBUF_SIZE - 1) / IOBUF_SIZE) * 12)
	+ FF_MIN_BUFFER_SIZE;
	if (max_packet_size > INT_MAX)
	return AVERROR(ENOMEM);
	if ((ret = ff_alloc_packet2(avctx, pkt, max_packet_size)) < 0)
	return ret;

	s->bytestream_start =
	s->bytestream = pkt->data;
	s->bytestream_end = pkt->data + pkt->size;

	crow_base = av_malloc((row_size + 32) << (s->filter_type == PNG_FILTER_VALUE_MIXED));
	if (!crow_base)
	goto fail;
	crow_buf = crow_base + 15; // pixel data should be aligned, but there's a control byte before it
	if (is_progressive) {
	progressive_buf = av_malloc(row_size + 1);
	if (!progressive_buf)
	goto fail;
	}
	if (is_progressive) {
	top_buf = av_malloc(row_size + 1);
	if (!top_buf)
	goto fail;
	}

	/* write png header */
	AV_WB64(s->bytestream, PNGSIG);
	s->bytestream += 8;

	AV_WB32(s->buf, avctx->width);
	AV_WB32(s->buf + 4, avctx->height);
	s->buf[8] = bit_depth;
	s->buf[9] = color_type;
	s->buf[10] = 0; /* compression type */
	s->buf[11] = 0; /* filter type */
	s->buf[12] = is_progressive; /* interlace type */

	png_write_chunk(&s->bytestream, MKTAG('I', 'H', 'D', 'R'), s->buf, 13);

	if (s->dpm) {
	AV_WB32(s->buf, s->dpm);
	AV_WB32(s->buf + 4, s->dpm);
	s->buf[8] = 1; /* unit specifier is meter */
	} else {
	AV_WB32(s->buf, avctx->sample_aspect_ratio.num);
	AV_WB32(s->buf + 4, avctx->sample_aspect_ratio.den);
	s->buf[8] = 0; /* unit specifier is unknown */
	}
	png_write_chunk(&s->bytestream, MKTAG('p', 'H', 'Y', 's'), s->buf, 9);

	/* put the palette if needed */
	if (color_type == PNG_COLOR_TYPE_PALETTE) {
	int has_alpha, alpha, i;
	unsigned int v;
	uint32_t *palette;
	uint8_t *alpha_ptr;

	palette = (uint32_t *)p->data[1];
	ptr = s->buf;
	alpha_ptr = s->buf + 256 * 3;
	has_alpha = 0;
	for(i = 0; i < 256; i++) {
	v = palette[i];
	alpha = v >> 24;
	if (alpha != 0xff)
	has_alpha = 1;
	*alpha_ptr++ = alpha;
	bytestream_put_be24(&ptr, v);
	}
	png_write_chunk(&s->bytestream, MKTAG('P', 'L', 'T', 'E'), s->buf, 256 * 3);
	if (has_alpha) {
	png_write_chunk(&s->bytestream, MKTAG('t', 'R', 'N', 'S'), s->buf + 256 * 3, 256);
	}
	}

	/* now put each row */
	s->zstream.avail_out = IOBUF_SIZE;
	s->zstream.next_out = s->buf;
	if (is_progressive) {
	int pass;

	for(pass = 0; pass < NB_PASSES; pass++) {
	/* NOTE: a pass is completely omitted if no pixels would be
	output */
	pass_row_size = ff_png_pass_row_size(pass, bits_per_pixel, avctx->width);
	if (pass_row_size > 0) {
	top = NULL;
	for(y = 0; y < avctx->height; y++) {
	if ((ff_png_pass_ymask[pass] << (y & 7)) & 0x80) {
	ptr = p->data[0] + y * p->linesize[0];
	FFSWAP(uint8_t*, progressive_buf, top_buf);
	png_get_interlaced_row(progressive_buf, pass_row_size,
	bits_per_pixel, pass,
	ptr, avctx->width);
	crow = png_choose_filter(s, crow_buf, progressive_buf, top, pass_row_size, bits_per_pixel>>3);
	png_write_row(s, crow, pass_row_size + 1);
	top = progressive_buf;
	}
	}
	}
	}
	} else {
	top = NULL;
	for(y = 0; y < avctx->height; y++) {
	ptr = p->data[0] + y * p->linesize[0];
	crow = png_choose_filter(s, crow_buf, ptr, top, row_size, bits_per_pixel>>3);
	png_write_row(s, crow, row_size + 1);
	top = ptr;
	}
	}
	/* compress last bytes */
	for(;;) {
	ret = deflate(&s->zstream, Z_FINISH);
	if (ret == Z_OK \|\| ret == Z_STREAM_END) {
	len = IOBUF_SIZE - s->zstream.avail_out;
	if (len > 0 && s->bytestream_end - s->bytestream > len + 100) {
	png_write_chunk(&s->bytestream, MKTAG('I', 'D', 'A', 'T'), s->buf, len);
	}
	s->zstream.avail_out = IOBUF_SIZE;
	s->zstream.next_out = s->buf;
	if (ret == Z_STREAM_END)
	break;
	} else {
	goto fail;
	}
	}
	png_write_chunk(&s->bytestream, MKTAG('I', 'E', 'N', 'D'), NULL, 0);

	pkt->size = s->bytestream - s->bytestream_start;
	pkt->flags \|= AV_PKT_FLAG_KEY;
	*got_packet = 1;
	ret = 0;

	the_end:
	av_free(crow_base);
	av_free(progressive_buf);
	av_free(top_buf);
	deflateEnd(&s->zstream);
	return ret;
	fail:
	ret = -1;
	goto the_end;
	}

	static av_cold int png_enc_init(AVCodecContext *avctx){
	PNGEncContext *s = avctx->priv_data;

	switch(avctx->pix_fmt) {
	case AV_PIX_FMT_RGBA:
	avctx->bits_per_coded_sample = 32;
	break;
	case AV_PIX_FMT_RGB24:
	avctx->bits_per_coded_sample = 24;
	break;
	case AV_PIX_FMT_GRAY8:
	avctx->bits_per_coded_sample = 0x28;
	break;
	case AV_PIX_FMT_MONOBLACK:
	avctx->bits_per_coded_sample = 1;
	break;
	case AV_PIX_FMT_PAL8:
	avctx->bits_per_coded_sample = 8;
	}

	avctx->coded_frame = av_frame_alloc();
	if (!avctx->coded_frame)
	return AVERROR(ENOMEM);

	avctx->coded_frame->pict_type = AV_PICTURE_TYPE_I;
	avctx->coded_frame->key_frame = 1;

	ff_dsputil_init(&s->dsp, avctx);

	s->filter_type = av_clip(avctx->prediction_method, PNG_FILTER_VALUE_NONE, PNG_FILTER_VALUE_MIXED);
	if(avctx->pix_fmt == AV_PIX_FMT_MONOBLACK)
	s->filter_type = PNG_FILTER_VALUE_NONE;

	if (s->dpi && s->dpm) {
	av_log(avctx, AV_LOG_ERROR, "Only one of 'dpi' or 'dpm' options should be set\n");
	return AVERROR(EINVAL);
	} else if (s->dpi) {
	s->dpm = s->dpi * 10000 / 254;
	}

	return 0;
	}

	static av_cold int png_enc_close(AVCodecContext *avctx)
	{
	av_frame_free(&avctx->coded_frame);
	return 0;
	}

	#define OFFSET(x) offsetof(PNGEncContext, x)
	#define VE AV_OPT_FLAG_VIDEO_PARAM \| AV_OPT_FLAG_ENCODING_PARAM
	static const AVOption options[] = {
	{"dpi", "Set image resolution (in dots per inch)", OFFSET(dpi), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 0x10000, VE},
	{"dpm", "Set image resolution (in dots per meter)", OFFSET(dpm), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 0x10000, VE},
	{ NULL }
	};

	static const AVClass pngenc_class = {
	.class_name = "PNG encoder",
	.item_name = av_default_item_name,
	.option = options,
	.version = LIBAVUTIL_VERSION_INT,
	};

	AVCodec ff_png_encoder = {
	.name = "png",
	.long_name = NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
	.type = AVMEDIA_TYPE_VIDEO,
	.id = AV_CODEC_ID_PNG,
	.priv_data_size = sizeof(PNGEncContext),
	.init = png_enc_init,
	.close = png_enc_close,
	.encode2 = encode_frame,
	.capabilities = CODEC_CAP_FRAME_THREADS \| CODEC_CAP_INTRA_ONLY,
	.pix_fmts = (const enum AVPixelFormat[]){
	AV_PIX_FMT_RGB24, AV_PIX_FMT_RGBA,
	AV_PIX_FMT_RGB48BE, AV_PIX_FMT_RGBA64BE,
	AV_PIX_FMT_PAL8,
	AV_PIX_FMT_GRAY8, AV_PIX_FMT_GRAY8A,
	AV_PIX_FMT_GRAY16BE,
	AV_PIX_FMT_MONOBLACK, AV_PIX_FMT_NONE
	},
	.priv_class = &pngenc_class,
	};