Fix waveform80#486

Quality is ignored for the MJPEG video encoder (but not the JPEG
image encoder)

Author: waveform80

docs/fov.rst

@@ -859,12 +859,11 @@ influence the camera's behaviour.
 The Still Port
 --------------
 
-Whenever the still port is used to capture images, it (briefly)
-forces the camera's mode to one of the two supported still modes (see
-:ref:`camera_modes`), meaning that images are captured using the full area of the
-sensor. It also uses a strong noise reduction algorithm on captured images so
-that they appear higher quality.
-.. They "appear" to be higher quality, or they "are" higher quality? This almost makes it seem like the images appear to be a higher quality than they actually are.
+Whenever the still port is used to capture images, it (briefly) forces the
+camera's mode to one of the two supported still modes (see
+:ref:`camera_modes`), meaning that images are captured using the full area of
+the sensor. It also uses a strong noise reduction algorithm on captured images
+so that they appear higher quality.
 
 The still port is used by the various :meth:`~PiCamera.capture` methods when
 their *use_video_port* parameter is ``False`` (which it is by default).

picamera/camera.py

@@ -1179,9 +1179,8 @@ def start_recording(
           to maintain. For the ``'h264'`` format, use values between 10 and 40
           where 10 is extremely high quality, and 40 is extremely low (20-25 is
           usually a reasonable range for H.264 encoding). For the ``mjpeg``
-          format, use JPEG quality values between 1 and 100 (where higher
-          values are higher quality). Quality 0 is special and seems to be
-          a "reasonable quality" default.
+          format, the quality is ignored (it can be specified without error
+          though); *bitrate* alone controls the quality of the output.
 
         * *quantization* - Deprecated alias for *quality*.
 

tests/test_record.py

@@ -62,7 +62,7 @@
     RecordingCase('h264',  '.h264', {'bitrate': 20000000, 'profile': 'main'}),
     RecordingCase('mjpeg', '.mjpg', {}),
     RecordingCase('mjpeg', '.mjpg', {'bitrate': 10000000}),
-    RecordingCase('mjpeg', '.mjpg', {'bitrate': 0, 'quality': 20}),
+    RecordingCase('mjpeg', '.mjpg', {'bitrate': 1000000}),
     ) + tuple(
     RecordingCase(fmt,     '.data', {})
     for fmt in RAW_FORMATS