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lavf/gif: trim unnecessarily long netscape ext code.

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Extension description comments are now placed along the avio calls, the
always defined macro removed, and the always true loop_count check as
well (loop option is bound to 0-65535).
This commit is contained in:
Clément Bœsch 2013-04-18 13:01:56 +02:00
parent 0a0e6877ff
commit b7a3f14360
1 changed files with 9 additions and 38 deletions
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45
libavformat/gif.c
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@ -27,12 +27,6 @@
#include "libavutil/log.h"
#include "libavutil/opt.h"
/* slows down the decoding (and some browsers don't like it) */
/* update on the 'some browsers don't like it issue from above:
* this was probably due to missing 'Data Sub-block Terminator'
* (byte 19) in the app_header */
#define GIF_ADD_APP_HEADER // required to enable looping of animated gif
static int gif_image_write_header(AVIOContext *pb, int width, int height,
int loop_count, uint32_t *palette)
{
@ -57,39 +51,16 @@ static int gif_image_write_header(AVIOContext *pb, int width, int height,
avio_w8(pb, 0); /* aspect ratio */
}
/* update: this is the 'NETSCAPE EXTENSION' that allows for looped animated
* GIF, see http://members.aol.com/royalef/gifabout.htm#net-extension
*
* byte 1 : 33 (hex 0x21) GIF Extension code
* byte 2 : 255 (hex 0xFF) Application Extension Label
* byte 3 : 11 (hex (0x0B) Length of Application Block
* (eleven bytes of data to follow)
* bytes 4 to 11 : "NETSCAPE"
* bytes 12 to 14 : "2.0"
* byte 15 : 3 (hex 0x03) Length of Data Sub-Block
* (three bytes of data to follow)
* byte 16 : 1 (hex 0x01)
* bytes 17 to 18 : 0 to 65535, an unsigned integer in
* lo-hi byte format. This indicate the
* number of iterations the loop should
* be executed.
* bytes 19 : 0 (hex 0x00) a Data Sub-block Terminator
*/
/* application extension header */
#ifdef GIF_ADD_APP_HEADER
if (loop_count >= 0 && loop_count <= 65535) {
avio_w8(pb, 0x21);
avio_w8(pb, 0xff);
avio_w8(pb, 0x0b);
// bytes 4 to 14
/* "NETSCAPE EXTENSION" for looped animation GIF */
avio_w8(pb, 0x21); /* GIF Extension code */
avio_w8(pb, 0xff); /* Application Extension Label */
avio_w8(pb, 0x0b); /* Length of Application Block */
avio_write(pb, "NETSCAPE2.0", sizeof("NETSCAPE2.0") - 1);
avio_w8(pb, 0x03); // byte 15
avio_w8(pb, 0x01); // byte 16
avio_w8(pb, 0x03); /* Length of Data Sub-Block */
avio_w8(pb, 0x01);
avio_wl16(pb, (uint16_t)loop_count);
avio_w8(pb, 0x00); // byte 19
}
#endif
avio_w8(pb, 0x00); /* Data Sub-block Terminator */
return 0;
}