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• FFMPEG - How to pipe RMS_level and pts_time metadata without generating unwanted metadata

  6 février 2020, par Tovi Newman

  I am trying to find the loudest (highest rms_level) moment in an audio file, but I need to pipe the metadata rather than write to a file.

  I converted the answer found here : [https://superuser.com/questions/1183663/determining-audio-level-peaks-with-ffmpeg][1]

  By removing the write to file command and adding a pipe.
  Here’s what I’ve got.

  ffmpeg -i loudSoft.mp3 -af astats=metadata=1:reset=1,ametadata=print:key=lavfi.astats.Overall.RMS_level -f null - 2> result.txt

  The only problem is, now I’ve got a lot of unwanted metadata before and after the RMS_level and pts_time data as well as [Parsed_ametadata_1 @ 0x7f9d42c37500] being printed on each line. None of that was being written when I was writing to a file instead of piping. (all I need is the time and the rms.)

  Here is an abridged version of what I get when I write to file :

  frame:0    pts:0       pts_time:0
  
  lavfi.astats.Overall.RMS_level=-inf
  
  frame:1    pts:47      pts_time:0.00106576
  
  lavfi.astats.Overall.RMS_level=-165.163347
  
  frame:2    pts:1199    pts_time:0.0271882
  
  lavfi.astats.Overall.RMS_level=-99.736394
  
  frame:3    pts:2351    pts_time:0.0533107
  
  lavfi.astats.Overall.RMS_level=-88.112282
  
  frame:4    pts:3503    pts_time:0.0794331
  
  lavfi.astats.Overall.RMS_level=-86.554314
  
  frame:5    pts:4655    pts_time:0.105556
  
  lavfi.astats.Overall.RMS_level=-82.977501
  
  frame:6    pts:5807    pts_time:0.131678
  
  lavfi.astats.Overall.RMS_level=-79.698739
  
  frame:7    pts:6959    pts_time:0.1578
  
  lavfi.astats.Overall.RMS_level=-76.629393
  
  frame:8    pts:8111    pts_time:0.183923
  
  lavfi.astats.Overall.RMS_level=-71.581211
  
  frame:9    pts:9263    pts_time:0.210045
  
  lavfi.astats.Overall.RMS_level=-75.038503
  
  frame:10   pts:10415   pts_time:0.236168

  And here is what I’m looking at :

  ffmpeg version 4.2.2 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with Apple clang version 11.0.0 (clang-1100.0.33.16)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/4.2.2_1 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/adoptopenjdk-13.0.1.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/adoptopenjdk-13.0.1.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  
    libavutil      56. 31.100 / 56. 31.100
  
    libavcodec     58. 54.100 / 58. 54.100
  
    libavformat    58. 29.100 / 58. 29.100
  
    libavdevice    58.  8.100 / 58.  8.100
  
    libavfilter     7. 57.100 /  7. 57.100
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  5.100 /  5.  5.100
  
    libswresample   3.  5.100 /  3.  5.100
  
    libpostproc    55.  5.100 / 55.  5.100
  
  Input #0, mp3, from 'loudSoft2.mp3':
  
    Metadata:
  
      encoder         : Lavf58.29.100
  
    Duration: 00:00:09.85, start: 0.025057, bitrate: 128 kb/s
  
      Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 128 kb/s
  
      Metadata:
  
        encoder         : Lavc58.54
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mp3 (mp3float) -> pcm_s16le (native))
  
  Press [q] to stop, [?] for help
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] frame:0    pts:0       pts_time:0
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] lavfi.astats.Overall.RMS_level=-inf
  
  Output #0, null, to 'pipe:':
  
    Metadata:
  
      encoder         : Lavf58.29.100
  
      Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
  
      Metadata:
  
        encoder         : Lavc58.54.100 pcm_s16le
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] frame:1    pts:47      pts_time:0.00106576
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] lavfi.astats.Overall.RMS_level=-165.163347
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] frame:2    pts:1199    pts_time:0.0271882
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] lavfi.astats.Overall.RMS_level=-99.736394
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] frame:3    pts:2351    pts_time:0.0533107
  
  
  
  
  
  *** MIDDLE OMITTED FOR BREVITY ***
  
  
  
  
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] lavfi.astats.Overall.RMS_level=-88.532185
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] frame:375  pts:430895  pts_time:9.77086
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] lavfi.astats.Overall.RMS_level=-88.594276
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] frame:376  pts:432047  pts_time:9.79698
  
  [Parsed_ametadata_1 @ 0x7f9d42c37500] lavfi.astats.Overall.RMS_level=-88.654138
  
  size=N/A time=00:00:09.82 bitrate=N/A speed=82.6x    
  
  video:0kB audio:1692kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Channel: 1
  
  [Parsed_astats_0 @ 0x7f9d42c37280] DC offset: 0.000001
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Min level: -0.000106
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Max level: 0.000115
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Min difference: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Max difference: 0.000077
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Mean difference: 0.000017
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS difference: 0.000022
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Peak level dB: -78.752617
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS level dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS peak dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS trough dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Crest factor: 3.126627
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Flat factor: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Peak count: 2
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Bit depth: 32/32
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Dynamic range: 76.274252
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Zero crossings: 246
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Zero crossings rate: 0.222624
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of NaNs: 0
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of Infs: 0
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of denormals: 0
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Channel: 2
  
  [Parsed_astats_0 @ 0x7f9d42c37280] DC offset: 0.000001
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Min level: -0.000106
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Max level: 0.000115
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Min difference: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Max difference: 0.000077
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Mean difference: 0.000017
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS difference: 0.000022
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Peak level dB: -78.752617
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS level dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS peak dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS trough dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Crest factor: 3.126627
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Flat factor: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Peak count: 2
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Bit depth: 32/32
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Dynamic range: 76.274252
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Zero crossings: 246
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Zero crossings rate: 0.222624
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of NaNs: 0
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of Infs: 0
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of denormals: 0
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Overall
  
  [Parsed_astats_0 @ 0x7f9d42c37280] DC offset: 0.000001
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Min level: -0.000106
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Max level: 0.000115
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Min difference: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Max difference: 0.000077
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Mean difference: 0.000017
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS difference: 0.000022
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Peak level dB: -78.752617
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS level dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS peak dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] RMS trough dB: -88.654138
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Flat factor: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Peak count: 2.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Bit depth: 32/32
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of samples: 1105
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of NaNs: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of Infs: 0.000000
  
  [Parsed_astats_0 @ 0x7f9d42c37280] Number of denormals: 0.000000

• 5 perfect feature combinations to use with Heatmaps and Session Recordings

  28 janvier 2020, par Jake Thornton — Uncategorized

  Gaining valuable insights by simply creating a heatmap or setting up recordings on your most important web pages is a good start, but using the Heatmaps and Session Recordings features in combination with other Matomo features is where the real magic happens.

  If you’re serious about significantly increasing conversions on your website to impact your bottom line, you need to accurately answer these questions :

  1. Are you analysing the most important pages that influence conversions ?
  2. Are you segmenting heatmaps and recordings towards your most valuable visitors ? 
  3. Are you using these features to create better customer journeys ?
  4. Have you identified current pain points for visitors before setting up heatmaps and recordings ?
  5. Are you learning what content resonates best for your audience ?

  With Matomo Analytics, you have the ability to integrate heatmaps and session recordings with all the features of a powerful web analytics platform, which means you get the complete picture of your visitor’s experience of your website.

  Here are five features that work with Heatmaps and Session Recordings to maximise conversions :

  1. Behaviour feature with Heatmaps

  Before creating heatmaps on pages you think are most important to your website, first check out Behaviour – Pages. Here you get valuable information around unique pageviews, bounce rate, average time on page and exit rates for every page on your website.

  Use this data as your starting point for heatmaps. Here you’ll identify current pain points for your visitors before using heatmaps to analyse their interactions on these pages.

  Here’s how to use the behaviour feature to determine which pages to setup heatmaps on :

  

  • Make sure you know what pages are generating the most unique page views, it could be your blog rather than your homepage
  • Which pages have the highest bounce rates – can you make some quick changes above-the-fold and see if this makes a difference
  • When the average time on page is high, why are visitors so engaged with these pages ? What keeps them reading ? Setup a heatmap to learn more
  • Reduce exit rates by moving them along to other pages on your website
  • Determine some milestones you want to achieve e.g. use heatmaps as your visual guide to improve average time on page, bounce rates and exit rates. A milestone could be that the exit rate for your previous blog was 34%, work towards getting this down to 30%

  Learn more about the Behaviour feature

  2. Ecommerce feature and Custom Segments

  If you run an ecommerce business, you may want to learn only about visitors who are more likely to be your customers. For example, if you find 65% of product sales come from customers based in New York, but visits to your product pages are from every state in the USA, how can you learn more specifically about visitors only from New York ?

  Using Segments to target a particular audience :

  • First, make sure you have created heatmaps and recordings on the popular product pages you want to learn about your visitor’s interactions
  • Note : Make sure the segment you create generates enough pageviews to apply a heatmap for more accurate results. We recommend a minimum of 1,000 page views per sample size.
  • Then create a custom Segment – search Ecommerce and find the Product Name and select the product. Learn how to do this here.

  

  Click on ‘Add a new segment’ or on the ‘edit’ link next to an existing segment name to open the segment editor :

  

  Click on any item on the left to see the list of information you can segment by. In this case search “City”, then select “Is” and in the third column search “New York” (example in the image above) :

  

  You can also use the search box at the bottom to search through the whole list.

  • This will give you insights across the Matomo platform based only on customers who purchased this product
  • Then go to the Ecommerce feature – and find Sales. Here you will learn what your most popular locations are for your product sales.

  

  • Once you know the location you want to segment, go back and update the custom Segment you just created. Click on the edit pencil icon and update it by selecting Add AND condition, and add the sub group you would like to track on the product page. In this example, select City – New York. Click Save & Apply.

  Now you should have successfully created a segment for your popular product page with visitors only from New York.

  Check out the heatmap or recordings you created for this page. You may be very surprised to see how this segment engaged with your website compared to all website visitors.

  Note : If you run a lead generation website you can use the Goals feature instead of Ecommerce to track the success metrics you need.

  Learn more about Segmentation

  3. Visitor Profiles within Session Recordings

  Seeing visitor location, device, OS and browser for your recordings is very valuable, but it’s even more valuable to integrate visitor profiles with session recordings as you get to see everything that visitor has done on your website … ever ! 

  What pages they visited before/after the recording, what actions they took, how long they spent on your website etc. All this is captured in the visitor profile of every individual session recording so you can see where exactly engaged viewers are in their journey with your business, for example :

  • How has this visitor behaved on your website in the past ? 
  • Is this visitor already a customer ? 
  • Is this the visitors first time to your website and
  • What other pages on your website are they interested in seeing in this session ?

  Use the visitor profiles feature within session recordings to understand the users better when watching each session.

  You get the full picture of what role the page you recorded played in the overall experience of your website’s visitor. And more importantly, to see if they took the desired action you wanted them to take.

  

  Learn more about Visitor Profiles

  4. Funnels feature (premium feature)

  The Funnels feature lets you see the customer journey from the first entry page through to the conversion page.

  

  Once you create a funnel, you can see the % of visitors who drop off between pages on their way to converting.

  In our example, you may then see page one to page two has a drop-off rate of 47%. Page two to page three 95% users drop-off rate and page three to page four 97.3% users drop-off rate.

  Why is the drop-off rate so high from page two to page three and why is the drop-off rate so low from page three to page four ?

  So, you may need to simplify things on page one because you may unknowingly be offering your visitor an easy way out of the funnel. Maybe the visitor is stuck reading your content and not understanding the value of your offering.

  Small tip for session recordings …

  With session recordings especially you can see firsthand through live recordings where exactly visitors click away from the page which exits them from your conversion funnel. Take note to see if this is a recurring issue with other visitors, then take action into fixing this hole.

  Whatever the case, work towards reducing drop-off rates through your conversion funnels by discovering where the problems exist, make changes and learn how these changes affect engagement through heatmaps and recordings.

  Learn more about Funnels

  5. A/B Testing feature (premium feature)

  Following on from the example with the Funnels feature, once you identify there is a problem in your conversion funnel, how do you know what is preventing visitors from taking an action that pushes them to the next page in the funnel ? You need to test different variations of content to see what works best for your visitors.

  A/B Testing lets you test a variety of things, including :

  • different headlines 
  • less copy vs more copy 
  • different call-to-actions
  • different colour schemes
  • entirely different page layouts

  

  Once you’ve created two or more variations of specific landing pages in the conversion funnel, see how visitors interacted differently between the variations of landing pages through your heatmaps and recordings.

  

  You may see that your visitors have scrolled further down the page because more content was provided or an important CTA button was clicked more due to a colour change. Whatever the case, using A/B testing with heatmaps and session recordings is an effective combination for increasing user engagement.

  Learn more about A/B Testing

  The conversion rate optimization (CRO) strategy

  CRO is the process of learning what the most valuable content/aspect of your website is and how to best optimize this for your visitors to increase conversion chances. 

  Heatmaps and session recordings play a vital role in this strategy, but it’s how you work these features in tandem with other valuable Matomo features that will give you the most actionable insights you need to grow your business.

  Want to learn how to create an effective CRO strategy ?

  Learn CRO strategies

• The ffmpeg webm_dash_manifest demuxer fails with webvtt subtitles

  30 janvier 2020, par Hyldrean

  I am trying to create a DASH manifest using ffmpeg and I encounter some difficulties with the subtitles. I get the error

  [webm_dash_manifest @ 0x55e19db48180] EBML header parsing failed
  
  [webm_dash_manifest @ 0x55e19db48180] Failed to read file headers
  
  subtitles.vtt: Operation not permitted

  The subtitles are encoded in the plain text webvtt format. I first assume that the EBML header are missing because the subtitles were not contained in a webm container. I then tried to create a webm file containing only the subtitles. It appears impossible.

  I think the problem comes from the webm_dash_manifest demuxer. It seeks metadata in a file with no metadata. However neither Google nor Stack Overflow give me an answer.

  The command I used :

  ffmpeg \
  
  -f webm_dash_manifest -i video.webm \
  
  -f webm_dash_manifest -i audio.webm \
  
  -f webm_dash_manifest -i subtitles.vtt \
  
  -map 0 -map 1 -map 2 \
  
  -c copy \
  
  -f webm_dash_manifest \
  
  -adaptation_sets "id=0,streams=0 id=1,streams=1 id=2,stream=2" \
  
  minimal.mpd

  and the ffmpeg output :

  ffmpeg version 3.2.14-1~deb9u1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  
    configuration: --prefix=/usr --extra-version='1~deb9u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 34.101 / 55. 34.101
  
    libavcodec     57. 64.101 / 57. 64.101
  
    libavformat    57. 56.101 / 57. 56.101
  
    libavdevice    57.  1.100 / 57.  1.100
  
    libavfilter     6. 65.100 /  6. 65.100
  
    libavresample   3.  1.  0 /  3.  1.  0
  
    libswscale      4.  2.100 /  4.  2.100
  
    libswresample   2.  3.100 /  2.  3.100
  
    libpostproc    54.  1.100 / 54.  1.100
  
  [webm_dash_manifest @ 0x55e19db17160] Could not find codec parameters for stream 0 (Video: vp9, none, 1280x534): unspecified pixel format
  
  Consider increasing the value for the 'analyzeduration' and 'probesize' options
  
  Input #0, webm_dash_manifest, from 'video.webm':
  
    Metadata:
  
      title           : Cloud Atlas
  
      ENCODER         : Lavf58.35.104
  
    Duration: 00:05:00.01, bitrate: 998 kb/s
  
      Chapter #0:0: start 0.000000, end 300.000000
  
      Metadata:
  
        title           : Chapter 01
  
      Stream #0:0(eng): Video: vp9, none, 1280x534, SAR 1:1 DAR 640:267, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default) (forced)
  
      Metadata:
  
        title           : Video @ 6.9 Mbps [frame B:188517 Avg QP:20.66]
  
        ENCODER         : Lavc58.66.100 libvpx-vp9
  
        DURATION        : 00:05:00.008000000
  
        webm_dash_manifest_duration: 300008
  
        webm_dash_manifest_initialization_range: 900
  
        webm_dash_manifest_file_name: video.webm
  
        webm_dash_manifest_track_number: 1
  
        webm_dash_manifest_cues_start: 37455991
  
        webm_dash_manifest_cues_end: 37457486
  
        webm_dash_manifest_bandwidth: 1420427
  
        webm_dash_manifest_cluster_keyframe: 1
  
        webm_dash_manifest_cue_timestamps: 298715
  
  Input #1, webm_dash_manifest, from 'audio.webm':
  
    Metadata:
  
      title           : Cloud Atlas
  
      ENCODER         : Lavf58.35.104
  
    Duration: 00:05:00.01, bitrate: 126 kb/s
  
      Chapter #1:0: start 0.000000, end 300.000000
  
      Metadata:
  
        title           : Chapter 01
  
      Stream #1:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)
  
      Metadata:
  
        title           : Audio Eng DTS 5.1 channels 24 bits @ 1509 Kbps cbr
  
        ENCODER         : Lavc58.66.100 libopus
  
        DURATION        : 00:05:00.007000000
  
        webm_dash_manifest_duration: 300007
  
        webm_dash_manifest_initialization_range: 838
  
        webm_dash_manifest_file_name: audio.webm
  
        webm_dash_manifest_track_number: 1
  
        webm_dash_manifest_cues_start: 4744091
  
        webm_dash_manifest_cues_end: 4745279
  
        webm_dash_manifest_bandwidth: 137531
  
        webm_dash_manifest_cluster_keyframe: 1
  
        webm_dash_manifest_cue_timestamps: 295000
  
  [webm_dash_manifest @ 0x55e19db48180] EBML header parsing failed
  
  [webm_dash_manifest @ 0x55e19db48180] Failed to read file headers
  
  subtitles.vtt: Operation not permitted

  I noticed that ffmpeg -f webm_dash_manifest -i subtitles.vtt suffices to reproduce the error.

  I have also tried without the -f webm_dash_manifest flag, with no success :

  ffmpeg \
  
  -f webm_dash_manifest -i video.webm \
  
  -f webm_dash_manifest -i audio.webm \
  
  -i subtitles.vtt \
  
  -map 0 -map 1 -map 2 \
  
  -c copy \
  
  -f webm_dash_manifest \
  
  -adaptation_sets "id=0,streams=0 id=1,streams=1 id=2,stream=2" minimal.mpd

  Output :

  ffmpeg version 3.2.14-1~deb9u1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  
    configuration: --prefix=/usr --extra-version='1~deb9u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 34.101 / 55. 34.101
  
    libavcodec     57. 64.101 / 57. 64.101
  
    libavformat    57. 56.101 / 57. 56.101
  
    libavdevice    57.  1.100 / 57.  1.100
  
    libavfilter     6. 65.100 /  6. 65.100
  
    libavresample   3.  1.  0 /  3.  1.  0
  
    libswscale      4.  2.100 /  4.  2.100
  
    libswresample   2.  3.100 /  2.  3.100
  
    libpostproc    54.  1.100 / 54.  1.100
  
  [webm_dash_manifest @ 0x557f55dd1160] Could not find codec parameters for stream 0 (Video: vp9, none, 1280x534): unspecified pixel format
  
  Consider increasing the value for the 'analyzeduration' and 'probesize' options
  
  Input #0, webm_dash_manifest, from 'video.webm':
  
    Metadata:
  
      title           : Cloud Atlas
  
      ENCODER         : Lavf58.35.104
  
    Duration: 00:05:00.01, bitrate: 998 kb/s
  
      Chapter #0:0: start 0.000000, end 300.000000
  
      Metadata:
  
        title           : Chapter 01
  
      Stream #0:0(eng): Video: vp9, none, 1280x534, SAR 1:1 DAR 640:267, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default) (forced)
  
      Metadata:
  
        title           : Video @ 6.9 Mbps [frame B:188517 Avg QP:20.66]
  
        ENCODER         : Lavc58.66.100 libvpx-vp9
  
        DURATION        : 00:05:00.008000000
  
        webm_dash_manifest_duration: 300008
  
        webm_dash_manifest_initialization_range: 900
  
        webm_dash_manifest_file_name: video.webm
  
        webm_dash_manifest_track_number: 1
  
        webm_dash_manifest_cues_start: 37455991
  
        webm_dash_manifest_cues_end: 37457486
  
        webm_dash_manifest_bandwidth: 1420427
  
        webm_dash_manifest_cluster_keyframe: 1
  
        webm_dash_manifest_cue_timestamps: 298715
  
  Input #1, webm_dash_manifest, from 'audio.webm':
  
    Metadata:
  
      title           : Cloud Atlas
  
      ENCODER         : Lavf58.35.104
  
    Duration: 00:05:00.01, bitrate: 126 kb/s
  
      Chapter #1:0: start 0.000000, end 300.000000
  
      Metadata:
  
        title           : Chapter 01
  
      Stream #1:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)
  
      Metadata:
  
        title           : Audio Eng DTS 5.1 channels 24 bits @ 1509 Kbps cbr
  
        ENCODER         : Lavc58.66.100 libopus
  
        DURATION        : 00:05:00.007000000
  
        webm_dash_manifest_duration: 300007
  
        webm_dash_manifest_initialization_range: 838
  
        webm_dash_manifest_file_name: audio.webm
  
        webm_dash_manifest_track_number: 1
  
        webm_dash_manifest_cues_start: 4744091
  
        webm_dash_manifest_cues_end: 4745279
  
        webm_dash_manifest_bandwidth: 137531
  
        webm_dash_manifest_cluster_keyframe: 1
  
        webm_dash_manifest_cue_timestamps: 295000
  
  Input #2, webvtt, from 'subtitles.vtt':
  
    Duration: N/A, bitrate: N/A
  
      Stream #2:0: Subtitle: webvtt
  
  Could not write header for output file #0 (incorrect codec parameters ?): Operation not permittedStream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #1:0 -> #0:1 (copy)
  
    Stream #2:0 -> #0:2 (copy)
  
      Last message repeated 1 times

  Note : [webm_dash_manifest @ 0x557f55dd1160] Could not find codec parameters for stream 0 (Video: vp9, none, 1280x534): unspecified pixel format is harmless according to this post.

  The subtitles have been extracted with ffmpeg :

  ffmpeg -i "Cloud Atlas.mkv" -map 0:6 -t 00:05:00 -c:s webvtt -dash 1 subtitles.vtt

  Thank you for reading my long post, I have no idea what to do next.

  EDIT : The WebM Project website says : ’Initial WebM release does not support subtitles’. Has someone heard of a new release ? Or a convenient way to create DASH manifest with subtitles ?