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• Using PyAV to encode mono audio to file, params match docs, but still causes Errno 22

  20 février 2023, par andrew8088

  While trying to use PyAV to encode live mono audio from a microphone to a compressed audio stream (using mp2 or flac as encoder), the program kept raising an exception ValueError: [Errno 22] Invalid argument.

  


  To remove the live microphone source as a cause of the problem, and to make the problematic code easier for others to run/test, I have removed the mic source and now just generate a pure tone as a sequence of input buffers.

  


  All attempts to figure out the missing or mismatched or incorrect argument have just resulted in seeing documentation and examples that are the same as my code.

  


  I would like to know from someone who has used PyAV successfully for mono audio what the correct method and parameters are for encoding mono frames into the mono stream.

  


  The package used is av 10.0.0 installed with
pip3 install av --no-binary av
so it uses my package-manager provided ffmpeg library, which is version 4.2.7.

  


  The problematic python code is :

  


  #!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Recreating an error 22 when encoding sound with PyAV.

Created on Sun Feb 19 08:10:29 2023
@author: andrewm
"""
import typing
import sys
import math
import fractions

import av
from av import AudioFrame

""" Ensure some PyAudio constants are still defined without changing 
    the PyAudio recording callback function and without depending 
    on PyAudio simply for reproducing the PyAV bug [Errno 22] thrown in 
    File "av/filter/context.pyx", line 89, in av.filter.context.FilterContext.push
"""
class PA_Stub():
    paContinue = True
    paComplete= False

pyaudio = PA_Stub()


"""Generate pure tone at given frequency with amplitude 0...1.0 at 
   sampling frewuency fs and beginning at phase offset 'phase'.
   Returns the new phase after the sinusoid has cycled over the 
   sampling window length.
"""
def generate_tone(
        freq:int, phase:float, amp:float, fs, samp_fmt, buffer:bytearray
) -> float:
    assert samp_fmt == "s16", "Only s16 supported atm"
    samp_size_bytes = 2
    n_samples = int(len(buffer)/samp_size_bytes)
    window = [int(0) for i in range(n_samples)]
    theta = phase
    phase_inc = 2*math.pi * freq / fs
    for i in range(n_samples):
        v = amp * math.sin(theta)
        theta += phase_inc
        s = int((2**15-1)*v)
        window[i] = s
    for sample_i in range(len(window)):
        byte_i = sample_i * samp_size_bytes
        enc = window[sample_i].to_bytes(
                2, byteorder=sys.byteorder, signed=True
        )
        buffer[byte_i] = enc[0]
        buffer[byte_i+1] = enc[1]
    return theta


channels = 1
fs = 44100  # Record at 44100 samples per second
fft_size_samps = 256
chunk_samps = fft_size_samps * 10  # Record in chunks that are multiples of fft windows.

# print(f"fft_size_samps={fft_size_samps}\nchunk_samps={chunk_samps}")

seconds = 3.0
out_filename = "testoutput.wav"

# Store data in chunks for 3 seconds
sample_limit = int(fs * seconds)
sample_len = 0
frames = []  # Initialize array to store frames

ffmpeg_codec_name = 'mp2'  # flac, mp3, or libvorbis make same error.

sample_size_bytes = 2
buffer = bytearray(int(chunk_samps*sample_size_bytes))
chunkperiod = chunk_samps / fs
total_chunks = int(math.ceil(seconds / chunkperiod))
phase = 0.0

### uncomment if you want to see the synthetic data being used as a mic input.
# with open("test.raw","wb") as raw_out:
#     for ci in range(total_chunks):
#         phase = generate_tone(2600, phase, 0.8, fs, "s16", buffer)
#         raw_out.write(buffer)
# print("finished gen test")
# sys.exit(0)
# #---- 

# Using mp2 or mkv as the container format gets the same error.
with av.open(out_filename+'.mp2', "w", format="mp2") as output_con:
    output_con.metadata["title"] = "My title"
    output_con.metadata["key"] = "value"
    channel_layout = "mono"
    sample_fmt = "s16p"

    ostream = output_con.add_stream(ffmpeg_codec_name, fs, layout=channel_layout)
    assert ostream is not None, "No stream!"
    cctx = ostream.codec_context
    cctx.sample_rate = fs
    cctx.time_base = fractions.Fraction(numerator=1,denominator=fs)
    cctx.format = sample_fmt
    cctx.channels = channels
    cctx.layout = channel_layout
    print(cctx, f"layout#{cctx.channel_layout}")
    
    # Define PyAudio-style callback for recording plus PyAV transcoding.
    def rec_callback(in_data, frame_count, time_info, status):
        global sample_len
        global ostream
        frames.append(in_data)
        nsamples = int(len(in_data) / (channels*sample_size_bytes))
        
        frame = AudioFrame(format=sample_fmt, layout=channel_layout, samples=nsamples)
        frame.sample_rate = fs
        frame.time_base = fractions.Fraction(numerator=1,denominator=fs)
        frame.pts = sample_len
        frame.planes[0].update(in_data)
        print(frame, len(in_data))
        
        for out_packet in ostream.encode(frame):
            output_con.mux(out_packet)
        for out_packet in ostream.encode(None):
            output_con.mux(out_packet)
        
        sample_len += nsamples
        retflag = pyaudio.paContinue if sample_lencode>

  


  If you uncomment the RAW output part you will find the generated data can be imported as PCM s16 Mono 44100Hz into Audacity and plays the expected tone, so the generated audio data does not seem to be the problem.

  


  The normal program console output up until the exception is :

  


  mp2 at 0x7f8e38202cf0> layout#4
Beginning
 5120
. 5120


  


  The stack trace is :

  


  Traceback (most recent call last):&#xA;&#xA;  File "Dev/multichan_recording/av_encode.py", line 147, in <module>&#xA;    ret_data, ret_flag = rec_callback(buffer, ci, {}, 1)&#xA;&#xA;  File "Dev/multichan_recording/av_encode.py", line 121, in rec_callback&#xA;    for out_packet in ostream.encode(frame):&#xA;&#xA;  File "av/stream.pyx", line 153, in av.stream.Stream.encode&#xA;&#xA;  File "av/codec/context.pyx", line 484, in av.codec.context.CodecContext.encode&#xA;&#xA;  File "av/audio/codeccontext.pyx", line 42, in av.audio.codeccontext.AudioCodecContext._prepare_frames_for_encode&#xA;&#xA;  File "av/audio/resampler.pyx", line 101, in av.audio.resampler.AudioResampler.resample&#xA;&#xA;  File "av/filter/graph.pyx", line 211, in av.filter.graph.Graph.push&#xA;&#xA;  File "av/filter/context.pyx", line 89, in av.filter.context.FilterContext.push&#xA;&#xA;  File "av/error.pyx", line 336, in av.error.err_check&#xA;&#xA;ValueError: [Errno 22] Invalid argument&#xA;&#xA;</module>

  


  edit : It's interesting that the error happens on the 2nd AudioFrame, as apparently the first one was encoded okay, because they are given the same attribute values aside from the Presentation Time Stamp (pts), but leaving this out and letting PyAV/ffmpeg generate the PTS by itself does not fix the error, so an incorrect PTS does not seem the cause.

  


  After a brief glance in av/filter/context.pyx the exception must come from a bad return value from res = lib.av_buffersrc_write_frame(self.ptr, frame.ptr)
  
Trying to dig into av_buffersrc_write_frame from the ffmpeg source it is not clear what could be causing this error. The only obvious one is a mismatch between channel layouts, but my code is setting the layout the same in the Stream and the Frame. That problem had been found by an old question pyav - cannot save stream as mono and their answer (that one parameter required is undocumented) is the only reason the code now has the layout='mono' argument when making the stream.

  


  The program output shows layout #4 is being used, and from https://github.com/FFmpeg/FFmpeg/blob/release/4.2/libavutil/channel_layout.h you can see this is the value for symbol AV_CH_FRONT_CENTER which is the only channel in the MONO layout.

  


  The mismatch is surely some other object property or an undocumented parameter requirement.

  


  How do you encode mono audio to a compressed stream with PyAV ?

  


• Homepage Design : Best Practices & Examples

  5 octobre 2022, par Erin

  Did you know users spend about 50 milliseconds deciding if they like your website’s homepage design or not ?

  With billions of websites and scrolling often done on the go, you have to make a strong first impression because the chances for a once-over are slim. 

  Learn how to design magnetically-appealing website homepages from this guide. 

  What is a homepage in web design ?

  Homepage is the front page of your website — a destination where users land when typing your website URL address. It’s located at the root of the website’s domain (e.g., matomo.org) or a subdomain (e.g., university.webflow.com).

  Design-wise a homepage has two goals :

  • Explain the purpose of the website and present overview information 
  • Provide top-level navigation to lower-level web pages (e.g., blog, sales pages, etc.) 

  Separately, a homepage is also the place where users will return each time they’ll feel stuck and want to start anew. Thus, your homepage website design should provide obvious navigation paths to other website areas.

  6 Must-Know Website Homepage Design Best Practices

  Behind every winning homepage design stands a detailed customer journey map. 

  A customer journey is a schematic representation of how site visitors will move around your website to accomplish various goals. 

  A good customer journey map lists different actions a user will take after landing on your website (e.g., browse product pages, save items to a wishlist, register an account, etc.) — and it does so for different audience segments. 

  

  Your homepage design should help users move from the first step on their journey (e.g., learning about your website) to the final one (e.g., converting to a paid customer). At the same time, your homepage should serve the needs of both new and returning visitors — prospects who may be at a different stage of their journey (e.g., consideration). 

  With the above in mind, let’s take a look at several website homepage design ideas and the reasons why they work. 

  1. Use Familiar Design Elements

  Whether you’re designing a new website or refreshing an old one, it’s always tempting to go “out of the box” — use horizontal scrolling, skip header navigation or include arty animations. 

  Bold design choices work for some brands, mainly those who aren’t using their website as a primary sales channel (e.g., luxury brands). 

  But unfamiliar design patterns can also intimidate a lot of shoppers. In one observational study, people were asked to guess where specific content (e.g., information on international calls) would be placed on a telecom website. 75% of users picked the same location. This means two things :

  • People already have expectations of where specific website information is typically placed 
  • Yet, one in four users struggles to identify the right areas even within standard website layouts

  So why make the job harder for them ? As UX consultant Peter Ramsey rightfully notes : 

  The truth is : designing the best experience isn’t about being unique, it’s about being easy. And guess what feels really easy to use ? Things that feel familiar.

  Therefore, analyse other homepage layout designs in your industry. Pay attention to the number and type of homepage screens and approaches to designing header/footer navigation. 

  Take some of those ideas as your “base”. Then make your homepage design on-brand with unique typography, icons, visuals and other graphic design elements.

  Take a cue from ICAM — a steel manufacturing company. Their niche isn’t typically exciting. Yet, their homepage design stops you in your tracks and tinkers your curiosity to discover more (even if you aren’t shopping for metalware). 

  

  The interesting part is that ICAM uses a rather standard homepage layout. You have a hero image in the first screen, followed by a multi-column layout of their industry expertise and an overview of manufacturers. 

  But this homepage design feels fresh because the company uses plenty of white space, bold typography and vibrant visuals. Also, they delay the creative twist (horizontal scrolling area) to the bottom of the homepage, meaning that it’s less likely to intimidate less confident web users. 

  2. Decide On The Optimal Homepage Layout 

  In web design, a homepage layout is your approach to visually organising different information on the screen. 

  Observant folks will notice that good homepage designs often have the same layout. For example, include a split-view “hero” screen with a call to action on the left and visuals (photo or video) on the left. 

  

  The reason for using similar layouts for website homepage design isn’t a lack of creativity. On the contrary, some layouts have become the “best practice” because they :

  • Offer a great user experience (UX) and don’t confuse first-time visitors 
  • Feel familiar and create a pleasurable sense of deja-vu among users 
  • Have proven to drive higher conversion rates through benchmarks and tests 

  Popular types of website homepage layouts : 

  • Single column – a classic option of presenting main content in a single, vertical column. Good choice for blogs, personal websites and simple corporate sites. 
  • Split screen layout divides the page in two equal areas with different information present. Works best for Ecommerce homepages (e.g., to separate different types of garments) or SaaS websites, offering two product types (e.g., a free personal product version and a business edition). 
  • Asymmetrical layout assumes dividing your homepage into areas of different size and styles. Asymmetry helps create specific focal points for users to draw their attention to the most prominent information. 
  • Grid of cards layout helps present a lot of information in a more digestible manner by breaking down bigger bulks of text into smaller cards — a graphic element, featuring an image and some texts. By tapping a card, users can then access extra content. 
  • Boxes are visually similar to cards, but can be of varying shape. For example, you can have a bigger header-width box area, followed by four smaller boxes within it. Both of these website layouts work well for Ecommerce. 
  • Featured image layout gives visuals (photos and videos) the most prominent placement on the homepage, with texts and other graphic design elements serving a secondary purpose. 
  • F-pattern layout is based on the standard eye movement most people have when reading content on the website. Eye tracking studies found that we usually pay the most attention to information atop of the page (header area), then scan horizontally before dripping down to the next vertical line until we find content that captures our attention. 

  User behaviour analytics (UBA) tools are the best way to determine what type of layout will work for your homepage. 

  For example, you can use Matomo Heatmaps and Session Recording to observe how users navigate your homepage, which areas or links they click and what blockers they face during navigation.

  

  Matomo can capture accurate behavioural insights because we track relative positions to elements within your websites. This approach allows us to provide accurate data for users with different browsers, operating systems, zoom-in levels and fonts. 

  The best part ? You can collect behavioural data from up to 100 different user segments to understand how different audience cohorts engage with your product.

  3. Include a One-Sentence Tagline

  A tagline is a one-line summary of what your company does and what its unique sales proposition (USP) is. It should be short, catchy and distinguish you from competitors.

  A modern homepage design practice is to include a call to action in the first screen. Why ? Because you then instantly communicate or remind of your value proposition to every user — and provide them with an easy way to convert whenever they are ready to do business with you. 

  Here’s how three companies with a similar product, a project management app, differentiate themselves through homepage taglines. 

  Monday.com positions itself as an operating system (OS) for work. 

  

  Basecamp emphasises its product simplicity and openly says that they are different from other overly-complex software. 

  

  Asana, in turn, addresses a familiar user pain point (siloed communication) that it attempts to fix with its product. 

  

  Coming up with the perfect homepage tagline is a big task. You may have plenty of ideas, but little confidence in what version will stick. 

  The best approach ? Let a series of A/B tests decide. You can test a roaster of homepage slogans on a rotating bi-weekly/monthly schedule and track how copy changes affect conversion rates. 

  With Matomo A/B test feature, you can create, track and manage all experiments straight from your web analytics app — and get consolidated reports on total page visitors and conversion rates per each tested variation. 

  

  Beyond slogans, you can also run A/B tests to validate submission form placements, button texts or the entire page layout. 

  For instance, you can benchmark how your new homepage design performs compared to the old version with a subset of users before making it publicly available. 

  4. Highlight The Main Tasks For The User

  Though casual browsing is a thing, most of us head to specific websites with a clear agenda — find information, compare prices, obtain services, etc. 

  Thus, your homepage should provide clear starting points for users’ main tasks (those you’ve also identified as conversion goals on your customer journey maps !).

  These tasks can include : 

  • Account registration 
  • Product demo request 
  • Newsletter sign-up 

  The best website homepage designs organically guide users through a set number of common tasks, one screen at a time. 

  Let’s analyse Sable homepage design. The company offers a no-fee bank account and a credit card product for soon-to-be US transplants. The main task a user has : Decide if they want to try Sable and hopefully open an account with them. 

  

  This mono-purpose page focuses on persuading a prospect that Sable is right for them. 

  The first screen hosts the main CTA with an animated drop-down arrow to keep scrolling. This is likely aimed at first-time visitors that just landed on the page from an online ad or social media post. 

  The second screen serves the main pitch — no-fee, no-hassle access to a US banking account that also helps you build your credit score. 

  The third screen encourages users to learn more about Sable Credit — the flagship product. For the sceptics, the fourth screen offers several more reasons to sign up for the credit product. 

  Then Sable moves on to pitching its second offering — a no-fee debit card with a cashback. Once again, the follow-up screen sweetens the deal by bringing up other perks (higher cashback for popular services like Amazon) and overcoming objections (no SSN required and multi-language support available). 

  The sequence ends with side-by-side product comparison and some extra social proof. 

  In Sable’s case, each homepage screen has a clear purpose and is designed to facilitate one specific user action — account opening. 

  For multi-product companies, the above strategy works great for designing individual landing pages. 

  5. Design Proper Navigation Paths

  All websites have two areas reserved for navigation : 

  • Header menu 
  • Footer menu 

  Designing an effective header menu is more important since it’s the primary tool visitors will use to discover other pages. 

  Your header menu can be :

  • Sticky — always visible as the person keeps scrolling. 
  • Static — e.g., a hidden drop-down menu. 

  If you go for a static header and have a longer homepage layout (e.g., 5+ screens), you also need to add extra navigation elements somewhere mid-page. Or else users might not figure out where to go next and merely bounce off. 

  You can do this by : 

  • Promoting other areas of your website (e.g., sub-category pages) by linking out to them 
  • Adding a carousel of “recent posts”, “recommended reads” and “latest products” 
  • Using buttons and CTAs to direct users towards specific actions (e.g., account registration) or assets (free eBook)

  For instance, cosmetics brand Typology doesn’t have a sticky header on the homepage. Instead, they prompt discovery by promoting different product categories (best sellers, bundles, latest arrivals) and their free skin diagnostic quiz — a great engagement mechanism to retain first time users.

  

  Once the user scrolls down to the bottom of the page, they should have an extra set of navigational options — aka footer links. 

  Again, these help steer the visitor towards discovering more content without scrolling back up to the top of your homepage. 

  Nielsen Norman Group says that people mostly use footers as :

  • A second chance to be convinced — after reading the entire homepage, the user is ready to give your product a go.
    
  • The last resort for hard-to-find content that’s not displayed in global header navigation (e.g., Terms and Conditions or shipping information pages).

  As a rule of thumb, you should designate the following information to the footer : 

  • Utility links (Contact page, Terms & Conditions, Privacy Policy, etc.) 
  • Secondary-task links (e.g., Career page, Investor Details, Media contacts, etc.) 
  • Brands within the organisation (if you operate several) 
  • Customer engagement link (email newsletters and social media buttons)

  The key is to keep the area compact — not more than one standard user screen resolution of 1280×720. 

  6. Show Users What’s Clickable (Or Not) 

  A homepage invites your site visitors on a journey. But if they don’t know which elements to click, they aren’t going to get anywhere.

  Good homepage design makes it obvious which page elements are clickable, i.e., can take the user to a new page or another segment of the homepage. 

  Here are several must-know homepage design tips for better on-page navigation : 

  • Use colour and underline or bold to highlight clickable words. Alternatively, you can change the browser cursor from a standard arrow into another element (e.g., a larger dot or a pointy finger) to indicate when the cursor hovers over a clickable website area. 
  • Make descriptive button texts that imply what will happen when a user clicks the page. Instead of using abstract and generic button texts like “see more” or “learn more”, try a more vibrant language like “dive in” for clicking through to a spa page. 
  • Use a unified hover area to show how different homepage design elements represent a single path or multiple navigation paths. When multiple items are encapsulated in one visual element (e.g., a box), users may be reluctant to click the image because they aren’t sure if it’s one large hit area leading to a single page or if there are multiple hit areas, leading to different pages. 

  Homepage of BEAUSiTE — a whimsical hotel in the Swiss Alps – embodies all of the above design principles. They change the cursor style whenever you scroll into a hit area, use emotive and creative micro-copy for all button texts and clearly distinguish between different homepage elements.

  

  How to Make Your Homepage Design Even More Impactful ? 

  Website homepage design is roughly 20% of pure design work and 80% of behind-the-scenes research. 

  To design a high-performing homepage you need to have data-backed answers to the following questions : 

  • Who are your primary and secondary target audiences ? 
  • Which tasks (1 to 4) you’d want to help them solve through your homepage ?

  You can get the answers to both questions from your web analytics data by using audience segmentation and page transition (behaviour flow) reports in Matomo. 

  Based on these, you can determine common user journeys and tasks people look to accomplish when visiting your website. Next, you can collect even more data with UBA tools  like heatmaps and user session recordings. Then translated the observed patterns into working homepage design ideas. 

  Improve your homepage design and conversion rates with Matomo. Start your free 21-day trial now ! 

  21 day free trial. No credit card required.

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• FFMPEG Settings for the most frame accurate seeking [closed]

  26 août 2022, par D.Bence

  What is the best ffmpeg settings for the most accurate seeking in hls stream ?

  


  Someone could explain to me what is the relation between the GOP size and seeking precision ?

  


  I experienced that seeking in hls (m3u8) video not as precise as pure mp4 video stream.