[FFmpeg-devel] aspect fuction

[rachel li]

1. What does code below mean?

video_enc->sample_aspect_ratio = av_d2q(frame_aspect_ratio*video_enc->height/video_enc->width, 255);

If the source is 720x480 aspect_ratio 1.333, then the result is 8/9. what does it mean?

2. I found this function does not take effect while outputting jpeg. The command line I use as follows:

-i  test.avi ?f image2 ?vcodec mjpeg ?aspect 1.3333  -y test%d.jpg

Because I found code as follows at mjpegenc.c

jpeg_put_comments

if (s->aspect_ratio_info /* && !lossless */)

    {

    /* JFIF header */

    put_marker(p, APP0);

    put_bits(p, 16, 16);

    ff_put_string(p, "JFIF", 1); /* this puts the trailing zero-byte too */

    put_bits(p, 16, 0x0201); /* v 1.02 */

    put_bits(p, 8, 0); /* units type: 0 - aspect ratio */

    put_bits(p, 16, s->avctx->sample_aspect_ratio.num);

    put_bits(p, 16, s->avctx->sample_aspect_ratio.den);

    put_bits(p, 8, 0); /* thumbnail width */

    put_bits(p, 8, 0); /* thumbnail height */

}

I found the condition is not satisfied, what does it mean?