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• MP4Box / FFMPEG concat loses audio after first clip

  17 novembre 2017, par user1615343

  So I am certainly no expert when it comes to either of these tools, but I have a web-based project that’s executing commands on an Amazon Linux server to concatenate two video files that are uploaded.

  Both files are converted to mp4s first using FFMPEG, and those play perfectly in a browser after conversion :

  ffmpeg -i file1.mpg -c:v libx264 -crf 22 -c:a aac -strict -2 -movflags faststart file2.mp4

  Then, I attempt to combine these two resulting mp4s into a single mp4. I tried using FFMPEG to do this but to no avail. Switching to try MP4Box got me much closer : the videos are concatenated together, but the audio stops playing at the end of the first clip, and the second clip is silent.

  MP4Box -force-cat -keepsys -add file.mp4 -cat file2.mp4 out.mp4

  I’ve tried varying versions of the above command with no better results. Any input is greatly appreciated.

  EDIT : info on .mp4 files using

  ffmpeg -i file1.mp4 -i file2.mp4

  ffmpeg -i 1510189259715DogRunsintoGlassDoor_315a03a8e20acfc.mp4 -i
  1510189273549NewhouseMoonMoonneverseenstairsbeforefunnydog_285a03a8e6aab25.mp4

  ffmpeg version N-61041-g52a2138 Copyright (c) 2000-2014 the FFmpeg
  developers

  built on Mar 2 2014 05:45:04 with gcc 4.6 (Debian 4.6.3-1)

  configuration : —prefix=/root/ffmpeg-static/64bit
  —extra-cflags=’-I/root/ffmpeg-static/64bit/include -static’ —extra-ldflags=’-L/root/ffmpeg-static/64bit/lib -static’ —extra-libs=’-lxml2 -lexpat -lfreetype’ —enable-static —disable-shared —disable-ffserver —disable-doc —enable-bzlib —enable-zlib —enable-postproc —enable-runtime-cpudetect —enable-libx264 —enable-gpl —enable-libtheora —enable-libvorbis —enable-libmp3lame —enable-gray —enable-libass —enable-libfreetype —enable-libopenjpeg —enable-libspeex —enable-libvo-aacenc —enable-libvo-amrwbenc —enable-version3 —enable-libvpx

  libavutil 52. 66.100 / 52. 66.100

  libavcodec 55. 52.102 / 55. 52.102

  libavformat 55. 33.100 / 55. 33.100

  libavdevice 55. 10.100 / 55. 10.100

  libavfilter 4. 2.100 / 4. 2.100

  libswscale 2. 5.101 / 2. 5.101

  libswresample 0. 18.100 / 0. 18.100

  libpostproc 52. 3.100 / 52. 3.100

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
  ’1510189259715DogRunsintoGlassDoor_315a03a8e20acfc.mp4’ :

  Metadata :

  major_brand : isom

  minor_version : 512

  compatible_brands : isomiso2avc1mp41

  encoder : Lavf55.33.100

  Duration : 00:00:04.92, start : 0.023220, bitrate : 634 kb/s

  Stream #0:0(und) : Video : h264 (High) (avc1 / 0x31637661), yuv420p,
  360x360 [SAR 1:1 DAR 1:1], 501 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc
  (default)

  Metadata :

  handler_name : VideoHandler

  Stream #0:1(und) : Audio : aac (mp4a / 0x6134706D), 44100 Hz, mono,
  fltp, 132 kb/s (default)

  Metadata :

  handler_name : SoundHandler

  Input #1, mov,mp4,m4a,3gp,3g2,mj2, from
  ’1510189273549NewhouseMoonMoonneverseenstairsbeforefunnydog_285a03a8e6aab25.mp4’ :

  Metadata :

  major_brand : isom

  minor_version : 512

  compatible_brands : isomiso2avc1mp41

  encoder : Lavf55.33.100

  Duration : 00:00:18.79, start : 0.023220, bitrate : 455 kb/s

  Stream #1:0(und) : Video : h264 (High) (avc1 / 0x31637661), yuv420p,
  362x360 [SAR 1:1 DAR 181:180], 320 kb/s, 29.94 fps, 29.94 tbr, 11976
  tbn, 59.88 tbc (default)

  Metadata :

  handler_name : VideoHandler

  Stream #1:1(eng) : Audio : aac (mp4a / 0x6134706D), 44100 Hz, stereo,
  fltp, 129 kb/s (default)

  Metadata :

  handler_name : SoundHandler

  At least one output file must be specified

• On WebP and Academic Exercises

  2 octobre 2010, par Multimedia Mike — General

  Yesterday, Google released a new still image format called WebP. To those skilled in the art, this new format will be recognizable as a single VP8 golden frame with a 20-byte header slapped on the front (and maybe a little metadata thrown in for good measure). We have a MultimediaWiki page and a sample ready to go.

  Further, I submitted a patch to ffmpeg-devel for FFmpeg’s img2 handling system to decode these files. FFmpeg should support processing these files soon… if anyone cares. This leads into…

  The Point, or Lack Thereof
  Since yesterday’s release, I have read a whirlwind of commentary about this format, much of it critical and of the “what’s the point ?” variety. For my part, I can respect academic exercises, a.k.a., just trying random stuff to see if you can make it work. That’s pretty much this blog’s entire raison d’être. But WebP transcends mere academic exercise ; Google seems to be trying to push it as a new web standard. I don’t see how the format can go anywhere based on criticisms raised elsewhere — e.g., see Dark Shikari’s thoughtful write-up — which basically boil down to WebP not solving any real problems, technical, legal, or otherwise.

  How did WebP come to be ? I strongly suspect some engineers noticed that JPEG is roughly the same as an MPEG-1 intraframe, so why not create a new still frame format based on VP8 intraframes ? Again, I can respect that thinking– I have pondered how a still image format would perform if based on VP3/Theora or Sorenson Video 1.

  Technically
  Google claims a significant size savings for WebP vs. standard JPEG. Assuming that’s true (and there will be no shortage of blog posts to the contrary), it will still be some time before WebP support will find its way into the majority of the web browser population.

  But this got me thinking about possible interim solutions. A website could store images compressed in both formats if it so chose. Then it could serve up a WebM image if the browser could support it, as indicated by the ‘Accept’ header in the HTTP request. It seems that a website might have to reference a generic image name such as <img src="some-picture.image"> ; the web server would have to recognize the .image extension and map it to either a .jpg or a .webp image depending on what the browser claims it is capable of displaying.

  Leftovers
  I appreciate that Dark Shikari has once again stuck his neck out and made a valiant — though often futile — effort to educate the internet’s masses. I long ago resigned myself to the fact that many people aren’t going to understand many of the most basic issues surrounding multimedia technology (i.e., moving pictures synchronized with audio). But apparently, this extends to still image formats as well. It was simultaneously humorous and disheartening to see commenters who don’t even understand the application of, e.g., PNG vs. JPEG : Ahem, “We already have a great replacement for jpg : .PNG”. Coupled with the typical accusations of MPEG tribalism, I remain impressed D. Shikari finds the will to bother.

  Still, I appreciate that the discussion has introduced me to some new image formats of which I was previously unaware, such as PGF and JPEG XR.

• More Cinepak Madness

  20 octobre 2011, par Multimedia Mike — Codec Technology

  Fellow digital archaeologist Clone2727 found a possible fifth variant of the Cinepak video codec. He asked me if I cared to investigate the sample. I assured him I wouldn’t be able to die a happy multimedia nerd unless I have cataloged all possible Cinepak variants known to exist in the wild. I’m sure there are chemistry nerds out there who are ecstatic when another element is added to the periodic table. Well, that’s me, except with weird multimedia formats.

  Background
  Cinepak is a video codec that saw widespread use in the early days of digital multimedia. To date, we have cataloged 4 variants of Cinepak in the wild. This distinction is useful when trying to write and maintain an all-in-one decoder. The variants are :

  1. The standard type : Most Cinepak data falls into this category. It decodes to a modified/simplified YUV 4:2:0 planar colorspace and is often seen in AVI and QuickTime/MOV files.
  2. 8-bit greyscale : Essentially the same as the standard type but with only a Y plane. This has only been identified in AVI files and is distinguished by the file header’s video bits/pixel field being set to 8 instead of 24.
  3. 8-bit paletted : Again, this is identified by the video header specifying 8 bits/pixel for a Cinepak stream. There is essentially only a Y plane in the data, however, each 8-bit value is a palette index. The palette is transported along with the video header. To date, only one known sample of this format has even been spotted in the wild, and it’s classified as NSFW. It is also a QuickTime/MOV file.
  4. Sega/FILM CPK data : Sega Saturn games often used CPK files which stored a variant of Cinepak that, while very close the standard Cinepak, couldn’t be decoded with standard decoder components.

  So, a flexible Cinepak decoder has to identify if the file’s video header specified 8 bits/pixel. How does it distinguish between greyscale and paletted ? If a file is paletted, a custom palette should have been included with the video header. Thus, if video bits/pixel is 8 and a palette is present, use paletted ; else, use greyscale. Beyond that, the Cinepak decoder has a heuristic to determine how to handle the standard type of data, which might deviate slightly if it comes from a Sega CPK file.

  The Fifth Variant ?
  Now, regarding this fifth variant– the reason this issue came up is because of that aforementioned heuristic. Basically, a Cinepak chunk is supposed to store the length of the entire chunk in its header. The data from a Sega CPK file plays fast and loose with this chunk size and the discrepancy makes it easy to determine if the data requires special handling. However, a handful of files discovered on a Macintosh game called “The Journeyman Project : Pegasus Prime” have chunk lengths which are sometimes in disagreement with the lengths reported in the containing QuickTime file’s stsz atom. This trips the heuristic and tries to apply the CPK rules against Cinepak data which, aside from the weird chunk length, is perfectly compliant.

  Here are the first few chunk sizes, as reported by the file header (stsz atom) and the chunk :

  size from stsz = 7880 (0x1EC8) ; from header = 3940 (0xF64)
  size from stsz = 3940 (0xF64) ; from header = 3940 (0xF64)
  size from stsz = 15792 (0x3DB0) ; from header = 3948 (0xF6C)
  size from stsz = 11844 (0x2E44) ; from header = 3948 (0xF6C)
  

  Hey, there’s a pattern here. If they don’t match, then the stsz size is an even multiple of the chunk size (2x, 3x, or 4x in my observation). I suppose I could revise the heuristic to state that if the stsz size is 2x, 3x, 4x, or equal to the chunk header, qualify it as compliant Cinepak data.

  Of course it feels impure, but software engineering is rarely about programmatic purity. A decade of special cases in the FFmpeg / Libav codebases are a testament to that.

  What’s A Variant ?
  Suddenly, I find myself contemplating what truly constitutes a variant. Maybe this was just a broken encoder program making these files ? And for that, I assign it the designation of distinct variation, like some sort of special, unique showflake ?

  Then again, I documented Magic Carpet FLIC as being a distinct variant of the broader FLIC format (which has an enormous number of variants as well).