gstreamer-1.0 on Raspberry Pi: cannot decode H.264 stream - raspberry-pi

Question

I'm trying to run a gstreamer-1.0 python script (see below, works fine on an ubuntu laptop) on a Raspberry Pi. However, it seems to be unable to decode the stream:
0:00:11.237415476 9605 0xafb0cc60 ERROR vaapidecode ../../../gst/vaapi/gstvaapidecode.c:1025:gst_vaapidecode_ensure_allowed_caps: failed to retrieve VA display
0:00:11.239490439 9605 0xafb0cc60 WARN decodebin gstdecodebin2.c:2087:connect_pad:<decodebin0> Link failed on pad vaapidecode0:sink
0:00:11.244097356 9605 0xafb0cc60 WARN uridecodebin gsturidecodebin.c:939:unknown_type_cb:<decoder> warning: No decoder available for type 'video/x-h264, stream-format=(string)byte-stream, alignment=(string)nal, width=(int)426, height=(int)240, framerate=(fraction)30/1, parsed=(boolean)true, pixel-aspect-ratio=(fraction)1/1, level=(string)2.1, profile=(string)main'.
I searched for information about the error (the results didn't enlighten me) and the warnings but couldn't really find much advice other than to install gstreamer1.0-libav which had already been installed. Consequently the decoder should be available.
What might be wrong here and how do I fix it?
This is the script:
#!/usr/bin/env python
# GST_DEBUG=3,python:5,gnl*:5 python 01_parsepipeline.py http://www.ustream.tv/channel/17074538 worst novideo.png
from __future__ import print_function
import sys
import gi
from gi.repository import GObject as gobject, Gst as gst
from livestreamer import Livestreamer, StreamError, PluginError, NoPluginError
import cv2
import numpy
def exit(msg):
print(msg, file=sys.stderr)
sys.exit()
class Player(object):
def __init__(self):
self.fd = None
self.mainloop = gobject.MainLoop()
# This creates a playbin pipeline and using the appsrc source
# we can feed it our stream data
self.pipeline = gst.parse_launch('uridecodebin uri=appsrc:// name=decoder \
decoder. ! videorate ! video/x-raw,framerate=1/1 ! tee name=t \
t. ! queue ! videoconvert ! video/x-raw,format=RGB ! appsink name=appsink \
decoder. ! queue ! audioconvert ! fakesink')
if self.pipeline is None:
exit("couldn't build pipeline")
decoder = self.pipeline.get_by_name('decoder')
if decoder is None:
exit("couldn't get decoder")
decoder.connect("source-setup", self.on_source_setup)
vsink = self.pipeline.get_by_name('appsink')
if vsink is None:
exit("couldn't get sink")
vsink.set_property("emit-signals", True)
vsink.set_property("max-buffers", 1)
vsink.connect("new-sample", self.on_new_sample)
# Creates a bus and set callbacks to receive errors
self.bus = self.pipeline.get_bus()
self.bus.add_signal_watch()
self.bus.connect("message::eos", self.on_eos)
self.bus.connect("message::error", self.on_error)
def on_new_sample(self, sink):
sample = sink.emit("pull-sample")
buf = sample.get_buffer()
caps = sample.get_caps()
height = caps.get_structure(0).get_value('height')
width = caps.get_structure(0).get_value('width')
(result, mapinfo) = buf.map(gst.MapFlags.READ)
if result == True:
arr = numpy.ndarray(
(height,
width,
3),
buffer=buf.extract_dup(0, buf.get_size()),
dtype=numpy.uint8)
resized_refimage = cv2.resize(refArray, (width, height))
diff = cv2.norm(arr, resized_refimage, cv2.NORM_L2)
buf.unmap(mapinfo)
s = "diff = " + str(diff)
print(s)
return gst.FlowReturn.OK
def exit(self, msg):
self.stop()
exit(msg)
def stop(self):
# Stop playback and exit mainloop
self.pipeline.set_state(gst.State.NULL)
self.mainloop.quit()
# Close the stream
if self.fd:
self.fd.close()
def play(self, stream):
# Attempt to open the stream
try:
self.fd = stream.open()
except StreamError as err:
self.exit("Failed to open stream: {0}".format(err))
# Start playback
self.pipeline.set_state(gst.State.PLAYING)
self.mainloop.run()
def on_source_setup(self, element, source):
# When this callback is called the appsrc expects
# us to feed it more data
print("source setup")
source.connect("need-data", self.on_source_need_data)
print("done")
def on_pad_added(self, element, pad):
string = pad.query_caps(None).to_string()
print(string)
if string.startswith('video/'):
#type = pad.get_caps()[0].get_name()
#print(type)
#if type.startswith("video"):
pad.link(self.vconverter.get_static_pad("sink"))
def on_source_need_data(self, source, length):
# Attempt to read data from the stream
try:
data = self.fd.read(length)
except IOError as err:
self.exit("Failed to read data from stream: {0}".format(err))
# If data is empty it's the end of stream
if not data:
source.emit("end-of-stream")
return
# Convert the Python bytes into a GStreamer Buffer
# and then push it to the appsrc
buf = gst.Buffer.new_wrapped(data)
source.emit("push-buffer", buf)
#print("sent " + str(length) + " bytes")
def on_eos(self, bus, msg):
# Stop playback on end of stream
self.stop()
def on_error(self, bus, msg):
# Print error message and exit on error
error = msg.parse_error()[1]
self.exit(error)
def main():
if len(sys.argv) < 4:
exit("Usage: {0} <url> <quality> <reference png image path>".format(sys.argv[0]))
# Initialize and check GStreamer version
gi.require_version("Gst", "1.0")
gobject.threads_init()
gst.init(None)
# Collect arguments
url = sys.argv[1]
quality = sys.argv[2]
refImage = sys.argv[3]
global refArray
image = cv2.imread(refImage)
refArray = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
# refArray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
refArray = cv2.blur(refArray, (3,3))
# Create the Livestreamer session
livestreamer = Livestreamer()
# Enable logging
livestreamer.set_loglevel("debug")
livestreamer.set_logoutput(sys.stdout)
# Attempt to fetch streams
try:
streams = livestreamer.streams(url)
except NoPluginError:
exit("Livestreamer is unable to handle the URL '{0}'".format(url))
except PluginError as err:
exit("Plugin error: {0}".format(err))
if not streams:
exit("No streams found on URL '{0}'".format(url))
# Look for specified stream
if quality not in streams:
exit("Unable to find '{0}' stream on URL '{1}'".format(quality, url))
# We found the stream
stream = streams[quality]
# Create the player and start playback
player = Player()
# Blocks until playback is done
player.play(stream)
if __name__ == "__main__":
main()

Answer 1

The pipeline you've set up appears to be trying to invoke a vaapi decoder to hardware-decode h264 - vaapi isn't available on the raspberry pi, since the closed source X server doesn't implement it. You may be able to use omxh264dec from the gstreamer1.0-omx package instead.
If not, you could do software h264 decoding, but that will be slower (maybe unacceptably slow on a raspberry pi).