mjpegdec: Properly set the context colorspace info

The JPEG spec requires it to be this.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
ffplay: eliminate pictq_prev_picture

Instead of directly rolling back the frame queue, keep the last displayed
picture in the queue and use a boolean variable to keep track if it is
displayed or not. This makes the code cleaner because it removes the
complicated logic in pictq_prev_picture.

There should be no change in functionality.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: pass simple integers to calculate_display_rect and set_default_window_size

No change in functionality.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: calculate SDL audio buffer size based on sample rate

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: decrease max audio callbacks per second

Too many audio callbacks per second can cause buffer underruns especially under
load. As now we take into accound the elapsed time after an audio callback when
determining current audio clock, it is not that important to use small buffer
sizes and frequent audio callbacks, so lets remove the comment.

Signed-off-by: Marton Balint <cus@passwd.hu>
ffplay: decrease audio_diff_threshold

Since audio clock calculations are more accurate now, it is safe to decrease
the sync treshold to compensate the larger buffers caused by less frequent
audio callbacks.

Signed-off-by: Marton Balint <cus@passwd.hu>
Merge commit '2deb614272e6faad8802c5341971d08c7272f74d'

* commit '2deb614272e6faad8802c5341971d08c7272f74d':
  mjpegdec: Properly set the context colorspace info

See: c11043aca7365add6c4c80b7cff80d22dde0eb94
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: decrease audio_diff_threshold
  ffplay: decrease max audio callbacks per second
  ffplay: calculate SDL audio buffer size based on sample rate
  ffplay: pass simple integers to calculate_display_rect and set_default_window_size
  ffplay: eliminate pictq_prev_picture

Merged-by: Michael Niedermayer <michaelni@gmx.at>