I'm using trying to stream live view of a SONY FDR-X1000V camera on desktop. I use python to call the API and download the package and use opencv to decode jpeg. When I run it, it can hardly catch one frame per second. Later I found out that the payload size of a jpeg can be 8MB. However, FDR-X1000V doesn't support changing live view size. But when I use the app on iPhone to do the liveview, it streams smoothly. So here is my question: 1. Is it normal that a jpeg payload can be as large as 8MB? 2. If so, how can I smoothly stream the live view?
Here is my code:
try:
result = api.do('startLiveview')
url = result['result'][0]
except KeyError:
print result
f = urllib2.urlopen(url)
buff = ''
chunk_size = 32768
for i in xrange(3000):
if len(buff) < chunk_size:
time_s = time.time()
buff = buff + f.read(chunk_size)
print "Download Speed %f KB/s"%(chunk_size/1000/(time.time() - time_s))
time_s = time.time()
start_code = ''.join(buff).find('$5hy')
# print "LCS time cost", time.time() - time_s
if start_code < 0:
buff = buff[-12:]
print "skip", len(buff)-12
elif start_code < 8:
buff = buff[8:]
else:
if start_code > len(buff) - 129:
buff = buff + f.read(chunk_size)
payload_type = ord(buff[start_code-7])
payload_size, = struct.unpack('<I', buff[start_code+4:start_code+8].ljust(4,'\0'))
padding_size = ord(buff[start_code+8])
print "Type:%d\tPayload:%d\tPadding:%d\t"%(payload_type,payload_size,padding_size)
buff = buff[start_code+128:]
if payload_type == 1:
if payload_size + padding_size > len(buff):
time_s = time.time()
download_size = payload_size+padding_size-len(buff)
buff = buff + f.read(download_size)
print "Download Speed %f KB/s"%(download_size/1000/(time.time() - time_s))
img_data = buff[:payload_size]
buff = buff[payload_size:]
time_s = time.time()
d = np.asarray(bytearray(img_data), dtype='uint8')
img = cv2.imdecode(d,cv2.IMREAD_COLOR)
cv2.imshow('postview',img)
cv2.waitKey(30)
# print "Decode time cost", time.time() - time_s
Some output:
Type:1 Payload:8410624 Padding:0
Download Speed 679.626326 KB/s
The answer from @Simon Wood and @Robert - Sony are all very useful! I made two mistakes in my code.
One is the payload size is 3 bytes instead of 4 bytes.
Another is that I assumed the byte order is little-endian instead of big-endian.
The project mentioned by @Simon Wood is a good one. Although it doesn't implement resynchronization on the 4-byte start code.
To make this right, I write my own codes in two methods to check and resynchronize it:
try:
result = api.do('startLiveview')
url = result['result'][0]
except KeyError:
print result
f = urllib2.urlopen(url)
#method 1
buff = ''
chunk_size = 8192
for i in xrange(300):
if len(buff) < chunk_size:
time_s = time.time()
buff = buff + f.read(chunk_size)
# print "Download Speed %f KB/s"%(chunk_size/1000/(time.time() - time_s))
time_s = time.time()
start_code = ''.join(buff).find('$5hy')
# print "LCS time cost", time.time() - time_s
if start_code < 0:
buff = buff[-12:]
print "skip", len(buff)-12
elif start_code < 8:
buff = buff[8:]
print "skip a header"
else:
if start_code > len(buff) - 129:
buff = buff + f.read(chunk_size)
start_byte = ord(buff[start_code - 8])
payload_type = ord(buff[start_code - 7])
sequence_num, = struct.unpack('>I', buff[start_code - 6:start_code - 4].rjust(4,'\0'))
time_stamp, = struct.unpack('>I', buff[start_code - 4:start_code].rjust(4,'\0'))
payload_size, = struct.unpack('>I', buff[start_code+4:start_code+7].rjust(4,'\0'))
padding_size = ord(buff[start_code+8])
print "StartByte:%d\t sequenceNum:%d\t timeStamp:%d\t Type:%d\t Payload:%d\t Padding:%d\t"%(
start_byte,sequence_num,time_stamp,payload_type,payload_size,padding_size)
buff = buff[start_code+128:]
if payload_type == 1:
if payload_size + padding_size > len(buff):
time_s = time.time()
download_size = payload_size+padding_size-len(buff)
buff = buff + f.read(download_size)
# print "Download Speed %f KB/s"%(download_size/1000/(time.time() - time_s))
img_data = buff[:payload_size]
buff = buff[payload_size:]
time_s = time.time()
d = np.asarray(bytearray(img_data), dtype='uint8')
img = cv2.imdecode(d,cv2.IMREAD_COLOR)
cv2.imshow('postview',img)
cv2.waitKey(10)
# print "Decode time cost", time.time() - time_s
#method 2
def checkbyte(f):
if f.read(4) == '$5hy':
return
state = 0
i = 1
while 1:
i+=1
if state == 0 :
if f.read(1) == '$':
state = 1
else:
state = 0
if state == 1 :
if f.read(1) == '5':
state = 2
else:
state = 0
if state == 2 :
if f.read(1) == 'h':
state = 3
else:
state = 0
if state == 3 :
if f.read(1) == 'y':
state = 4
else:
state = 0
if state == 4 :
print 'skip', i
return
for i in xrange(300):
buff = f.read(8)
start_byte ord(buff[0])
payload_type, = struct.unpack('>I',buff[1].rjust(4,'\0'))
sequence_num, = struct.unpack('>I',buff[2:4].rjust(4,'\0'))
time_stamp, = struct.unpack('>I',buff[4:8])
#payload header
checkbyte(f)
buff = f.read(124)
payload_size, = struct.unpack('>I',buff[0:3].rjust(4,'\0'))
padding_size= ord(buff[3])
print "StartByte:%d\t sequenceNum:%d\t timeStamp:%d\t Type:%d\t Payload:%d\t Padding:%d\t"%(
start_byte,sequence_num,time_stamp,payload_type,payload_size,padding_size)
d = f.read(payload_size)
if padding_size > 0:
f.read(padding_size)
if payload_type == 1:
# Type = 0x01
d = np.asarray(bytearray(d), dtype='uint8')
img = cv2.imdecode(d,cv2.IMREAD_COLOR)
cv2.imshow('postview',img)
cv2.waitKey(1)
print api.do('stopLiveview')