写这个程序，正是大名鼎鼎的开源音视频解码编码库FFMPEG2.5.3版本
在ffmpeg-2.5.3\libavcodec\mpeg4videodec.c
static int decode_user_data(Mpeg4DecContext *ctx, GetBitContext *gb)
{
MpegEncContext *s = &ctx->m;
char buf[256];
int i;
int e;
int ver = 0, build = 0, ver2 = 0, ver3 = 0;
char last;
for (i = 0; i < 255 && get_bits_count(gb) < gb->size_in_bits; i++) {
if (show_bits(gb, 23) == 0)
break;
buf[i] = get_bits(gb, 8);
}
buf[i] = 0;
/* divx detection */
e = sscanf(buf, "DivX%dBuild%d%c", &ver, &build, &last);
if (e < 2)
e = sscanf(buf, "DivX%db%d%c", &ver, &build, &last);
if (e >= 2) {
ctx->divx_version = ver;
ctx->divx_build = build;
s->divx_packed = e == 3 && last == 'p'; <<<< ------ 就是这个地方
if (s->divx_packed && !ctx->showed_packed_warning) {
av_log(s->avctx, AV_LOG_INFO, "Video uses a non-standard and "
"wasteful way to store B-frames ('packed B-frames'). "
"Consider using a tool like VirtualDub or avidemux to fix it.\n");
ctx->showed_packed_warning = 1;
}
}
/* libavcodec detection */
e = sscanf(buf, "FFmpe%*[^b]b%d", &build) + 3;
if (e != 4)
e = sscanf(buf, "FFmpeg v%d.%d.%d / libavcodec build: %d", &ver, &ver2, &ver3, &build);
if (e != 4) {
e = sscanf(buf, "Lavc%d.%d.%d", &ver, &ver2, &ver3) + 1;
if (e > 1)
build = (ver << 16) + (ver2 << 8) + ver3;
}
if (e != 4) {
if (strcmp(buf, "ffmpeg") == 0)
ctx->lavc_build = 4600;
}
if (e == 4)
ctx->lavc_build = build;
/* Xvid detection */
e = sscanf(buf, "XviD%d", &build);
if (e == 1)
ctx->xvid_build = build;
return 0;
}
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