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• ffmpeg video slides vertically after 'Invalid buffer size, packet size expected frame_size' error (vsync screen tearing glitch) ?

  7 juillet 2020, par GlabbichRulz

  I have a video which i want to cut and crop using opencv and ffmpeg.

  


  

  


  I want the output to be H265, so i am using a ffmpeg subprocess (writing frame bytes to stdin) as explained here. This is a minimum version of my code that leads to the error :

  


  import os, shlex, subprocess, cv2, imutils

VIDEO_DIR = '../SoExample' # should contain a file 'in.mpg'
TIMESPAN = (3827, 3927)  # cut to this timespan (frame numbers)
CROP = dict(min_x=560, max_x=731, min_y=232, max_y=418)  # crop to this area

#  calculate output video size
size = (CROP['max_x']-CROP['min_x'], CROP['max_y']-CROP['min_y'])  # (w,h)
# ffmpeg throws an error when having odd dimensions that are not dividable by 2,
# so i just add a pixel to the size and stretch the original image by 1 pixel later.
size_rounded = (size[0]+1 if size[0] % 2 != 0 else size[0],
                size[1]+1 if size[1] % 2 != 0 else size[1])

# read input video
vid_path_in = os.path.join(VIDEO_DIR, 'in.mpg')
cap = cv2.VideoCapture(vid_path_in)
fps = int(cap.get(cv2.CAP_PROP_FPS))

# generate and run ffmpeg command
ffmpeg_cmd = (f'/usr/bin/ffmpeg -y -s {size_rounded[0]}x{size_rounded[1]} -pixel_format'
              + f' bgr24 -f rawvideo -r {fps} -re -i pipe: -vcodec libx265 -pix_fmt yuv420p'
              + f' -crf 24 -x265-params "ctu=64" "{os.path.join(VIDEO_DIR, "out.mp4")}"')
print("using cmd", ffmpeg_cmd)
process = subprocess.Popen(shlex.split(ffmpeg_cmd), stdin=subprocess.PIPE)

# seek to the beginning of the cutting timespan and loop through frames of input video
cap.set(cv2.CAP_PROP_POS_FRAMES, TIMESPAN[0])
frame_returned = True
while cap.isOpened() and frame_returned:
    frame_returned, frame = cap.read()
    frame_number = cap.get(cv2.CAP_PROP_POS_FRAMES) - 1

    # check if timespan end is not reached yet
    if frame_number < TIMESPAN[1]:

        # crop to relevant image area
        frame_cropped = frame[CROP['min_y']:CROP['max_y'],
                              CROP['min_x']:CROP['max_x']]

        # resize to even frame size if needed:
        if size != size_rounded:
            frame_cropped = imutils.resize(frame_cropped, width=size_rounded[0],
                                           height=size_rounded[1])

        # Show processed image using opencv: I see no errors here.
        cv2.imshow('Frame', frame_cropped)

        # Write cropped video frame to input stream of ffmpeg sub-process.
        process.stdin.write(frame_cropped.tobytes())
    else:
        break

    # Press Q on keyboard to exit earlier
    if cv2.waitKey(25) & 0xFF == ord('q'):
        break

process.stdin.close()  # Close and flush stdin
process.wait()         # Wait for sub-process to finish
process.terminate()    # Terminate the sub-process

print("Done!")


  


  Unfortunately, my output looks like this :

  


  

  


  The output should not include this vertical sliding glitch. Does anyone know how to fix it ?

  


  My console output for aboves script shows :

  


  using cmd /usr/bin/ffmpeg -y -s 172x186 -pixel_format bgr24 -f rawvideo -r 23 -i pipe: -vcodec libx265 -pix_fmt yuv420p -crf 24 -x265-params "ctu=64" "../SoExample/out.mp4"
ffmpeg version 3.4.6-0ubuntu0.18.04.1 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
  configuration: --prefix=/usr --extra-version=0ubuntu0.18.04.1 --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-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --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-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  WARNING: library configuration mismatch
  avcodec     configuration: --prefix=/usr --extra-version=0ubuntu0.18.04.1 --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-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --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-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared --enable-version3 --disable-doc --disable-programs --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libtesseract --enable-libvo_amrwbenc
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Input #0, rawvideo, from 'pipe:':
  Duration: N/A, start: 0.000000, bitrate: 17659 kb/s
    Stream #0:0: Video: rawvideo (BGR[24] / 0x18524742), bgr24, 172x186, 17659 kb/s, 23 tbr, 23 tbn, 23 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> hevc (libx265))
x265 [info]: HEVC encoder version 2.6
x265 [info]: build info [Linux][GCC 7.2.0][64 bit] 8bit+10bit+12bit
x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
x265 [info]: Main profile, Level-2 (Main tier)
x265 [info]: Thread pool created using 4 threads
x265 [info]: Slices                              : 1
x265 [info]: frame threads / pool features       : 2 / wpp(3 rows)
x265 [warning]: Source height < 720p; disabling lookahead-slices
x265 [info]: Coding QT: max CU size, min CU size : 64 / 8
x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra
x265 [info]: ME / range / subpel / merge         : hex / 57 / 2 / 2
x265 [info]: Keyframe min / max / scenecut / bias: 23 / 250 / 40 / 5.00
x265 [info]: Lookahead / bframes / badapt        : 20 / 4 / 2
x265 [info]: b-pyramid / weightp / weightb       : 1 / 1 / 0
x265 [info]: References / ref-limit  cu / depth  : 3 / on / on
x265 [info]: AQ: mode / str / qg-size / cu-tree  : 1 / 1.0 / 32 / 1
x265 [info]: Rate Control / qCompress            : CRF-24.0 / 0.60
x265 [info]: tools: rd=3 psy-rd=2.00 rskip signhide tmvp strong-intra-smoothing
x265 [info]: tools: deblock sao
Output #0, mp4, to '../SoExample/out.mp4':
  Metadata:
    encoder         : Lavf57.83.100
    Stream #0:0: Video: hevc (libx265) (hev1 / 0x31766568), yuv420p, 172x186, q=2-31, 23 fps, 11776 tbn, 23 tbc
    Metadata:
      encoder         : Lavc57.107.100 libx265
[rawvideo @ 0x564ebd221aa0] Invalid buffer size, packet size 51600 < expected frame_size 95976    
Error while decoding stream #0:0: Invalid argument
frame=  100 fps= 30 q=-0.0 Lsize=      36kB time=00:00:04.21 bitrate=  69.1kbits/s speed=1.25x    
video:32kB audio:0kB subtitle:0kB other streams:0kB global headers:2kB muxing overhead: 12.141185%
x265 [info]: frame I:      1, Avg QP:22.44  kb/s: 179.77  
x265 [info]: frame P:     29, Avg QP:24.20  kb/s: 130.12  
x265 [info]: frame B:     70, Avg QP:29.99  kb/s: 27.82   
x265 [info]: Weighted P-Frames: Y:0.0% UV:0.0%
x265 [info]: consecutive B-frames: 20.0% 3.3% 16.7% 43.3% 16.7% 

encoded 100 frames in 3.35s (29.83 fps), 59.01 kb/s, Avg QP:28.23
Done!


  


  As you can see, there is an error : Invalid buffer size, packet size 51600 < expected frame_size 95976 Error while decoding stream #0:0: Invalid argument, do you think this could be the cause to the shown problem ? I am not sure, as in the end, it tells me all 100 frames would have been encoded.

  


  In case you want to reproduce this on the exact same video, you can find actions1.mpg in the UCF Aerial Action Dataset.

  


  I would greatly appreciate any help as i am really stuck on this error.

  


• Matomo vs WP-Statistics – which web analytics plugin suits you best ?

  2 avril 2020, par Joselyn Khor — Analytics Tips, Plugins

  Due to the endless choices, you may be wondering which web analytics plugin (GA, Slimstat or WP-Statistics) to choose from on the WordPress directory. If the choice is between WP-Statistics and Matomo for WordPress, we’ve got you covered. Have a look at which could be the best option for you. Our team tested the WP-Statistics plugin to see how it compares. It’s hard not to be biased, but we’ll try our best to give you a fair assessment.

  The main considerations in this article : 

  • General overview
  • General comparison
  • Similarities
  • Differences
  • Three notable feature category comparisons
  • Which tool suits you better ?

  General overview

  What’s Matomo Analytics for WordPress ?

  Matomo for WordPress is a free, privacy-friendly web analytics plugin that lets you understand website visitors and how they behave on your site. With comprehensive insights, you get the opportunity to increase conversions, and the know-how to improve your website. 

  It lets you undertake essential analysis by tracking information, such as, where visitors are coming from, what your most popular pages are, and how visitors are using your site.

  In addition to the fundamentals, the tool also allows for advanced tracking and analysis with features that give you a full understanding of behavioural patterns and website performance. This enables you to optimise your WordPress website to increase sales or engagement.

  It offers a complete analytics package with the bonuses of 100% data ownership, no data sampling, and GDPR compliance. 

  What’s WP-Statistics ?

  WP-Statistics is currently the most used self-hosted WordPress statistics plugin. It provides reports that let you analyse who your visitors are, where they’re coming from, and to an extent what they’re doing on your website.

  Like Matomo for WordPress, it gives you an understanding of your audience which helps you make decisions on how to improve your website for more conversions. 

  As it’s self-hosted on your own WordPress servers it can be seen as a privacy-friendly choice with a few tweaks (more on this below).

  Like Matomo for WordPress, it gives you an understanding of your audience which helps you make decisions on how to improve your website for more conversions. 

  General comparison

  Let’s compare the installation process and the dashboards that get installed in your WordPress.

  Installation

  Both Matomo and WP-Statistics are installed directly in your WordPress so you’ll be able to see your analytics reports right in your WordPress dashboard. You can install them both straight from the WordPress Directory.

  The installation process for both plugins is beginner-friendly. You simply need to find them on the WordPress directory, click on ‘Install Now’, and tracking should start immediately in your WordPress dashboard.

  Dashboard

  For the main Matomo platform you’ll see :

  • Visitors – Overview, Visits Log, Real-time, Real-time Map, Locations, Devices, Software, Times, User IDs, Custom Variables, User Type
  • Behaviour – Pages, Entry Pages, Exit Pages, Page titles, Site Search, Outlinks, Downloads, Events, Contents, Engagement, Transitions, Users Flow, Top Paths, Page Author, Page Location, Page Type, Crawling errors
  • Acquisition – Overview, All Channels, Search Engine & Keywords, Websites, Social Networks, Campaigns, Campaign URL Builder, Crawling overview
  • Ecommerce – Overview, Ecommerce Log, Products, Sales, Multi Attribution
  • Goals – Overview, Multi Attribution, Choose Goals, Manage Goals
  • These may be worded differently from WP-Statistics, but they show you all the information you need to know about your traffic, pages, etc.

  Previous

  Next

  In the dashboard for WP-Statistics you’ll see :

  • Overview, Hits, Online, Referrers, Search Words, Search Engines, Pages, Visitors, Categories, Tags, Authors, Browsers, Top Visitors Today
  • These are the only things you can see in the dashboard. So you can’t click into them for a drop down section to get deeper insights. 
  •  

  

  Key similarities between Matomo and WP-Statistics

  • Free to use
  • Self-hosted – All data collected is stored only within your own servers, no third parties have rights over your data, and logs or report data will never be sent to other servers. 
  • Beginner-friendly – Both offer simple reporting for people who are very much beginners and only want basic insights. With Matomo the advantage is also that you can get more details should you ever want/need to.

  Key differences between Matomo and WP-Statistics

  The main differences fall in these categories : features, privacy, documentation/support, security, active development, extensibility, price and ads.

  Features : 

  WP-Statistics – On a fundamental level, WP-Statistics is focused on simplicity and the basics. There are fewer reports than Matomo and they function on a level that suits beginners who are interested in seeing only the numbers of visitors on the website, and how often each page is viewed. 

  Matomo – provides an interface with similar simplicity. However, there is also a more feature-rich and more comprehensive user interface available. In addition to the basics, Matomo offers features like Goals, Ecommerce, in the free version which show a deeper level of insight. WP Statistics does not let you track essentials like Goals or Ecommerce.

  Privacy : 

  WP-Statistics – One of the concerns we wish to raise here is for data privacy. There doesn’t appear to be an opt-out option in WP-Statistics, which could be problematic for some privacy laws such as GDPR. There’s also no documentation on this.

  We were a bit concerned to see that WP-Statistics didn’t have IP anonymization enabled by default. Considering the IP address is personal data, it means you are not compliant with privacy laws such as the GDPR when you use this plugin unless you tweak the settings. They mentioned : “In previous versions, there was an option called Hash IP. When Hash IP was activated, the IP addresses wouldn’t be stored in the database, but instead, a unique hash would be used. In this new version, an option has been added to store IPs anonymously. This option is active by default.” However, when we installed this and tested it on multiple WordPress installations, this option was not active by default. 

  Matomo – has more measures in place to ensure privacy is respected, such as, opt-outs. Due to the stringent privacy features in place, Matomo is well equipped to ensure GDPR compliance. Matomo has an abundance of user guides and FAQs you can follow to configure your platform to fully comply with GDPR. There’s even an 12-step compliant checklist. The most compelling proof is that the leading voice on GDPR – The European Commission uses Matomo Analytics. 

  Documentation/Support : 

  WP-Statistics – has little documentation, FAQs, and no support.

  Matomo – has thousands of FAQs and user guides, as well as a dedicated support team and forum you can turn to for help. Should you ever run into any issue, this might be something important to consider.

  The contrast in support between WP-Statistics and Matomo for WordPress :

  

  

  Security :

  Matomo takes protecting your data very seriously. We have a security bounty programme giving security researchers money should they find any security issues. Matomo also performs a security review for every new release. We couldn’t find anything similar in WP-Statistics.

  Active development : 

  WP Statistics – doesn’t seem to have active development. The last change in this plugin was over three months ago (source : https://github.com/wp-statistics/wp-statistics/commits/master) and in general, only 10 people really contributed to it (source : https://github.com/wp-statistics/wp-statistics/graphs/contributors, the graphs shows little contributor activity.) 

  Matomo – has been built by hundreds of contributors (source : https://github.com/matomo-org/matomo/graphs/contributors), and is actively maintained by multiple developers including developers who work on this full time. This means you can rest assured that Matomo will be there for you in the future, it will receive regular improvements.

  Extensibility :

  WP-Statistics – have a section on their website offering customisation but for a price. 

  Matomo – should you want any changes and have some developer knowledge or some developers at hand, you can completely customise and extend Matomo for free. There are also one hundred additional plugins available for Matomo for free. 
  

  Price :

  The main WordPress plugins ‘WP Statistics‘ and ‘Matomo Analytics – Ethical Stats. Powerful Insights.‘ are both free.

  WP Statistics and Matomo also sell paid add-ons. However, WP-Statistics’ paid add-ons are ones already integrated in Matomo for free. These basic features are provided as the development team believe they’re necessities to a fully functional analytics platform. 

  Ads :

  WP Statistics shows you ads, whereas Matomo doesn’t.

  Three most notable feature category comparisons

  Both Matomo and WP-Statistics have basic tracking categories in the WP dashboard. In addition, Matomo has feature categories that can be expanded e.g. when clicked, Visitors drops down to reveal 11 more features. 

  We’ll compare three feature categories : Visitors, Behaviour, and Acquisitions.

  1. Visitors (WP-Statistics) vs Visitors (Matomo)

  Let’s dive into how each analytics platform provides insight into the visitors feature category.

  WP-Statistics

  

  WP-Statistics – We can see WP-Statistics gives you bare bones tracking capabilities so you don’t get a really detailed picture of your visitors. It allows you to monitor users currently online in real-time, which is useful to look at the most recent activity on your site. WP-Statistics doesn’t offer a dropdown section to see more about your visitor’s behavioural patterns. There is no Visitors category in WP-Statistics, just individual features in the dashboard but we can group three options together to compare with Matomo’s Visitors category, these are : Online, Browsers, Top Visitors Today.

  Matomo

  

  

  Comparison

  Matomo – In comparison, Matomo has a Visitors category with a dropdown list that lets you drill deeper into what your visitors are doing. It lets you evaluate every action an individual user has taken on your website which is compiled into a full historical profile. Matomo gives an in-depth view. E.g. you can look at individual visit logs, locations, and devices.

  This lets you see what the life-time journey of an active user looks like, or perhaps you want to see what a profile looks like for a user who comes back time-and-time again without ever purchasing ; there is no better way to gain insights to these journeys and this is why the Visitor Profiles feature is so widely used by Matomo users.

  2. Pages tracking (WP-Statistics) vs Behaviour (Matomo)

  For this comparison, WP-Statistics has a few features that can be combined to compare with Matomo’s Behaviour category. 

  WP-Statistics

  

  The Pages section in WP-Statistics gives a basic look at your most popular pages so you know which pages get more visits and those which aren’t performing. This helps with content improvement. You can also see other features in this Behaviour category like Browsers and Hits – these also provide basic stats to help you get a general sense of visitor behaviour. 

  Matomo

  

  Comparison :

  Matomo on the other hand has stats that go into greater detail. The features under the Behaviour section of the tool let you draw actionable conclusions e.g. seeing that a page has a higher exit rate than it’s supposed to, so you optimise that page to prevent people leaving and help them progress through your website. 

  Not only can you see popular pages, you can look at : which page people viewed first when they visited your website ; which page they left from ; what people search for on your site ; and see how people are flowing through pages. Most importantly you can see how each of these reports perform over time so you can improve engagement and conversions on your website.

  3. Referrers (WP-Statistics) vs Acquisition (Matomo)

  For this comparison, WP-Statistics has a few features that can be combined to compare with Matomo’s Acquisition category. 

  WP-Statistics

  

  WP-Statistics gives you Referrers, Search Words, and Search Engines. Which give a basic understanding of the channels that work best for you. This is helpful to know where to focus more of your attention.

  Matomo

  

  Comparison :

  With Matomo you see multiple layers of stats to understand how your acquisition channels are performing. So you can see tables of data that drill into visits, downloads, bounce rate, and newsletter sign ups. For example seeing that Facebook is the channel bringing in the most visitors to your site. This gives you a better sense of which acquisition strategy is working for your site. 

  Who suits WP-Statistics

  This is a great starter pack for people who want a lightweight, functional statistics plugin that gives you a basic overview of website hits and visitors. It’s very easy to use, so it’s great for beginners and those who want simple tracking. If you have basic goals for your website or blog’s success then WP-Statistics is enough for you to get numbers on visitors, page views, and hits, but won’t be suitable for a larger-scale business or organisation. 

  It’s suited for hobby websites, blogs, and freelancers who want simple, effective stats tracking, who don’t need detailed insights on site performance or tracking. 

  Who suits Matomo

  Matomo can be used for the same basic reporting, but has the capability for you to go deeper into more advanced reporting in a different UI if you need it. It’s an option that can work for a wider range of users – from beginners to analysts. There are features to suit all skill levels. This complete suite of features makes it a more comprehensive tool, as you can get more out of it. Ideal not only for bloggers and beginners, but also powerful enough to suit businesses, privacy-respecting organisations, and those who would benefit from conversion optimisation features. 

  You can draw insights from all stages of the customer journey – you’ll track behavioural patterns as soon as visitors enter your site, to their progression through your site, and ultimately to conversion and exit. It’s also an ethical choice because you get 100% data ownership. 

  If you’d like to look deeper into your data then Matomo would also be suitable for you. Matomo’s UI is lean, very easy to learn and shouldn’t overwhelm users in the way another tool like Google Analytics might do. If you think Matomo suits you best, you can install it for free now.

  Advantages of using Matomo

  Truly privacy-respecting

  There’s no messing about when it comes to privacy. As a lot of users are based in Europe, Matomo adheres to the strictest privacy laws and can be counted on as a privacy-respecting tool that’s used by many government entities. Needing to comply with major privacy laws (GDPR) in Europe means Matomo can proudly ensure users are making the ethical choice.

  GDPR compliance

  You mitigate the risks of getting caught out and fined for breaching GDPR regulations. There’s a complete list of documentation, guides, information, and tools to make sure you’re on the right side of GDPR. 

  All-rounder

  Matomo gives you a clearer picture of your visitors which helps you make better decisions for your website overall. The support and documentation is thorough which means you get more out of your Matomo experience.

  Conclusion

  Both tools will do you justice in terms of fundamental reporting, but Matomo Analytics will outshine if you want a greater understanding of your website and want to carry out deeper levels of analysis.

  You can draw useful insights with WP-Statistics so it has to be said that they are doing something right with an entry-level offering. The simplicity is great, but you won’t really get more than a basic idea of how your site is performing.

  On the flipside, this simplicity could also be a double-edged sword for WP-Statistics in that it’s too simplistic to draw actionable insights. If you’re wanting to know anything that could increase sales, conversions or subscribers – then you wouldn’t really get the reports to do so. 

  WP-Statistics also falls short when it comes to updates and support. So a major difference can be seen in support, active development, ads, security, documentation, which many people may think about until they’re in trouble and find they need these resources. Matomo offers support, continuous product development, and extensive documentation. There are also no ads, making it more enjoyable to use.

  One thing we’d like to raise awareness about is WP-Statistics’ claims of being privacy-respecting without much documentation to back up those claims. There is a lack of privacy features which could put some website owners at risk of non-compliance. Just be sure to check that you’ve carried out the steps to comply with the privacy laws in your country.

  Matomo makes it clear that privacy is essential as is compliance to privacy laws like GDPR. The strength also lies in the peace of mind you get from a tool that’s used by global privacy leaders such as the European Commission. 

• Libav Transcoding to H264 : Frames being dropped

  21 juin 2014, par roman

  I’m sorry if my question isn’t too well formulated, I’m only now getting started with FFmpeg and Libav. I’m not too knowledgable about media formats either, I pretty much learned all I know about the topic this past month. I’ve been doing as much research as I can, and have gotten pretty far, but I’ve only now gotten to the point where I’m almost unsure what my question actually is ! These are more like observations, but hopefully some of the experts can help me out here.

  I’m trying to transcode Gifs into MP4s using FFmpeg’s libraries, but I’m running into a strange issue when using the H264 Codec. In my transcoding loop, I keep a count of the number of frames that I write out (by verifying the return value of av_write_frame). In a particular sample, I count a total of 166 frames written out. If I examine FFmpeg’s converted file using FFprobe (the functionality I’m wanting to emulate using my program, a conversion from Gif to MP4), FFmpeg’s output file also seems to have 166 frames, but when I examine my output with FFprobe, I seem to only have 144 frames. What I find a bit interesting is that if I simply change my codec from H264 to MPEG4, my output appears to have the 166 frames, matching FFmpeg’s output and my counter. I get very similar results with different Gif files, where my counter of frames written matches FFmpeg’s output’s frame count, but my output seems to drop some frames.

  Encoder settings :

  ostream_codec_context->codec_id = CODEC_IN_USE;  //CODEC_ID_H264 or CODEC_ID_MPEG4
  
  ostream_codec_context->pix_fmt = AV_PIX_FMT_YUV420P;
  
  ostream_codec_context->codec_type = AVMEDIA_TYPE_VIDEO;
  
  ostream_codec_context->flags = CODEC_FLAG_GLOBAL_HEADER;
  
  ostream_codec_context->profile = FF_PROFILE_MPEG4_SIMPLE;
  
  
  
  ostream_codec_context->gop_size = istream_codec_context->gop_size;
  
  ostream_codec_context->time_base = istream_codec_context->time_base;
  
  
  
  ostream_codec_context->width  = (istream_codec_context->width  / 2) * 2;
  
  ostream_codec_context->height = (istream_codec_context->height / 2) * 2;    

  Transcoding loop :

  I’ve omitted some error-checking code and debugging statements

  avformat_write_header(oformat_context, NULL);
  
  while (av_read_frame(iformat_context, &packet) == 0 ) 
  
  {
  
     if (packet.stream_index == istream_index) 
  
     {   
  
        avcodec_decode_video2(istream_codec_context, ipicture, &full_frame, &packet);
  
        if (full_frame) 
  
        {
  
           sws_scale(image_conversion_context, 
  
                     (uint8_t const * const *) ipicture->data,
  
                     ipicture->linesize, 0, istream_codec_context->height,
  
                     opicture->data, opicture->linesize);
  
  
  
           opicture->pts = av_rescale_q(packet.pts, istream_codec_context->time_base,
  
                                        ostream->time_base);
  
  
  
           ret = avcodec_encode_video2(ostream_codec_context, &packet, 
  
                                       opicture, &got_packet);
  
           if (!ret)
  
           {
  
              ret = av_write_frame(oformat_context, &packet);
  
              if (ret < 0)
  
                 num_frames_written++;
  
           }
  
        }
  
     }
  
     av_free_packet(&packet);
  
     av_init_packet(&packet);
  
  }

  I’m also having issues with my output’s bit-rate. I can try setting it with the rest of my encoder settings, but the bit-rate that FFprobe shows is not the same as what I give the codec context. I tried setting the bit-rate to constant values just to see how it affected my output, and although my output’s bit-rate isn’t the same as what I give it, I found that my input definitely seems to influence the output’s actual bit-rate. I found a post that seems to be dealing with my issue, but the solution listed there does not seem to fix my issue.

  http://ffmpeg.org/pipermail/libav-user/2012-July/002492.html

  Another thing worth mentioning is that my various time bases don’t seem to match up with those of FFmpeg’s output. Notably, my output’s TBC seems to be twice the inverse of my output codec context’s time base. I’m not too sure if this is an issue with the Gif file format, my output codec context’s always seems to be set to 1/100.

  Bit-rate calculation and setting

  int calculated_br = istream_codec_context->time_base.den *     
  
                      avpicture_get_size(AV_PIX_FMT_YUV420P, ostream_codec_context->width, 
  
                                         ostream_codec_context->height);    
  
  
  
  ostream_codec_context->bit_rate = calculated_br;
  
  ostream_codec_context->rc_min_rate = calculated_br;
  
  ostream_codec_context->rc_max_rate = calculated_br;
  
  ostream_codec_context->rc_buffer_size = calculated_br;

  I’ve got a hunch that all these issues could be related to me not setting my PTS/DTS correctly, even though my output’s pts/dts values match those of FFmpeg’s output.

  I would appreciate some help,
  Thank you !