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• Official RealVideo Specifications

  29 juillet 2010, par Multimedia Mike — General

  A little birdie tipped me off to a publicly-accessible URL on the Helix community site (does anyone actually use Helix ?) that contains a bunch of specifications for RealVideo 8 and 9. I have been sifting through the documents to see exactly what they contain as the different files seem to be higher revisions of the same documents. Here is the title, date, and version of each PDF document :

  • RNDecoderPerformanceARM.pdf : Decoder Performance on StrongARM and XScale ; May 12, 2003 ; Version 1.1
  • rv89_decoder_summary.pdf : RealVideo 8/9 Combo Decoder Summary ; October 23, 2002 ; Version 1.0
  • rv9_dec_external_spec_v14.pdf : RealVideo 9 External Specification ; November 7, 2003 ; Version 1.4
  • rv8_dec_external_spec_v20.pdf : RealVideo 8 External Specification ; September 19, 2002 ; Version 2.0
  • RV8DecoderExternalSpecificationv201.pdf : RealVideo 8 External Specification ; October 20, 2006 ; Version 2.01
  • RV8DecoderExternalSpecificationv202.pdf : RealVideo 8 External Specification ; April 23, 2007 ; Version 2.02
  • RV8DecoderExternalSpecificationv203.pdf : RealVideo 8 External Specification ; July 20, 2007 ; Version 2.03
  • RV8DecoderExternalSpecificationv21.pdf : RealVideo 8 External Specification ; September 11, 2007 ; Version 2.1
  • RV9DecoderExternalSpecificationv15.pdf ; RealVideo 9 External Specification ; January 26, 2002 ; Version 1.5
  • RV9DecoderExternalSpecificationv16.pdf ; RealVideo 9 External Specification ; August 17, 2005 ; Version 1.6
  • RV9DecoderExternalSpecificationv18.pdf ; RealVideo 9 External Specification ; September 11, 2007 ; Version 1.8

  Additionally, there is an Excel spreadsheet entitled realvideo-faq.xls that appears to contain some general tech support advice for using Real’s official code. There are also 3 ZIP archives which contain profiling information about the official source code (post processing and entropy decoding top the charts which is no big surprise).

  I guess the latest version of each document (the ones dated September 11, 2007) are worth mirroring. Unfortunately, those latest document versions use a terrible font.

• Linux Media Player Survey Circa 2001

  2 septembre 2010, par Multimedia Mike — General

  Here’s a document I scavenged from my archives. It was dated September 1, 2001 and I now publish it 9 years later. It serves as sort of a time capsule for the state of media player programs at the time. Looking back on this list, I can’t understand why I couldn’t find MPlayer while I was conducting this survey, especially since MPlayer is the project I eventually started to work for a few months after writing this piece.

  For a little context, I had been studying multimedia concepts and tech for a year and was itching to get my hands dirty with practical multimedia coding. But I wanted to tackle what I perceived as unsolved problems– like playback of proprietary codecs. I didn’t want to have to build a new media playback framework just to start working on my problems. So I surveyed the players available to see which ones I could plug into and use as a testbed for implementing new decoders.

  Regarding Real Player, I wrote : “We’re trying to move away from the proprietary, closed-source “solutions”. Heh. Was I really an insufferable open source idealist back in the day ?

  Anyway, here’s the text with some Where are they now ? commentary [in brackets] :

  ---

  Towards an All-Inclusive Media Playing Solution for Linux

  I don’t feel that the media playing solutions for Linux set their sights high enough, even though they do tend to be quite ambitious.

  I want to create a media player for Linux that can open a file, figure out what type of file it is (AVI, MOV, etc.), determine the compression algorithms used to encode the audio and video chunks inside (MPEG, Cinepak, Sorenson, etc.) and replay the file using the best audio, video, and CPU facilities available on the computer.

  Video and audio playback is a solved problem on Linux ; I don’t wish to solve that problem again. The problem that isn’t solved is reliance on proprietary multimedia solutions through some kind of WINE-like layer in order to decode compressed multimedia files.

  Survey of Linux solutions for decoding proprietary multimedia
  updated 2001-09-01

  AVI Player for XMMS
  This is based on Avifile. All the same advantages and limitations apply.
  [Top Google hit is a Freshmeat page that doesn’t indicate activity since 2001-2002.]

  Avifile
  This player does a great job at taking apart AVI and ASF files and then feeding the compressed chunks of multimedia data through to the binary Win32 decoders.

  The program is written in C++ and I’m not very good at interpreting that kind of code. But I’m learning all over again. Examining the object hierarchy, it appears that the designers had the foresight to include native support for decoders that are compiled into the program from source code. However, closer examination reveals that there is support for ONE source decoder and that’s the “decoder” for uncompressed data. Still, I tried to manipulate this routine to accept and decode data from other codecs but no dice. It’s really confounding. The program always crashes when I feed non-uncompressed data through the source decoder.
  [Lives at http://avifile.sourceforge.net/ ; not updated since 2006.]

  Real Player
  There’s not much to do with this since it is closed source and proprietary. Even though there is a plugin architecture, that’s not satisfactory. We’re trying to move away from the proprietary, closed-source “solutions”.
  [Still kickin’ with version 11.]

  XAnim
  This is a well-established Unix media player. To his credit, the author does as well as he can with the resources he has. In other words, he supports the non-proprietary video codecs well, and even has support for some proprietary video codecs through binary-only decoders.

  The source code is extremely difficult to work with as the author chose to use the X coding format which I’ve never seen used anywhere else except for X header files. The infrastructure for extending the program and supporting other codecs and file formats is there, I suppose, but I would have to wrap my head around the coding style. Maybe I can learn to work past that. The other thing that bothers me about this program is the decoding approach : It seems that each video decoder includes routines to decompress the multimedia data into every conceivable RGB and YUV output format. This seems backwards to me ; it seems better to have one decoder function that decodes the data into its native format it was compressed from (e.g., YV12 for MPEG data) and then pass that data to another layer of the program that’s in charge of presenting the data and possibly converting it if necessary. This layer would encompass highly-optimized software conversion routines including special CPU-specific instructions (e.g., MMX and SSE) and eliminate the need to place those routines in lots of other routines. But I’m getting ahead of myself.
  [This one was pretty much dead before I made this survey, the most recent update being in 1999. Still, we owe it much respect as the granddaddy of Unix multimedia playback programs.]

  Xine
  This seems like a promising program. It was originally designed to play MPEGs from DVDs. It can also play MPEG files on a hard drive and utilizes the Xv extensions for hardware YUV playback. It’s also supposed to play AVI files using the same technique as Avifile but I have never, ever gotten it to work. If an AVI file has both video and sound, the binary video decoder can’t decode any frames. If the AVI file has video and no sound, the program gets confused and crashes, as far as I can tell.

  Still, it’s promising, and I’ve been trying to work around these crashes. It doesn’t yet have the type of modularization I’d like to see. Right now, it tailored to suit MPEG playback and AVI playback is an afterthought. Still, it appears to have a generalized interface for dropping in new file demultiplexers.

  I tried to extend the program for supporting source decoders by rewriting w32codec.c from scratch. I’m not having a smooth time of it so far. I’m able to perform some manipulations on the output window. However, I can’t get the program to deal with an RGB image format. It has trouble allocating an RGB surface with XvShmCreateImage(). This isn’t suprising, per my limited knowledge of X which is that Xv applies to YUV images, but it could also apply to RGB images as well. Anyway, the program should be able to fall back on regular RGB pixmaps if that Xv call fails.

  Right now, this program is looking the most promising. It will take some work to extend the underlying infrastructure, but it seems doable since I know C quite well and can understand the flow of this program, as opposed to Avifile and its C++. The C code also compiles about 10 times faster.
  [My home project for many years after a brief flirtation with MPlayer. It is still alive ; its latest release was just a month ago.]

  XMovie
  This library is a Quicktime movie player. I haven’t looked at it too extensively yet, but I do remember looking at it at one point and reading the documentation that said it doesn’t support key frames. Still, I should examine it again since they released a new version recently.
  [Heroine Virtual still puts out some software but XMovie has not been updated since 2005.]

  XMPS
  This program compiles for me, but doesn’t do much else. It can play an MP3 file. I have been able to get MPEG movies to play through it, but it refuses to show the full video frame, constricting it to a small window (obviously a bug).
  [This project is hosted on SourceForge and is listed with a registration date of 2003, well after this survey was made. So the project obviously lived elsewhere in 2001. Meanwhile, it doesn’t look like any files ever made it to SF for hosting.]

  XTheater
  I can’t even get this program to compile. It’s supposed to be an MPEG player based on SMPEG. As such, it probably doesn’t hold much promise for being easily extended into a general media player.
  [Last updated in 2002.]

  GMerlin
  I can’t get this to compile yet. I have a bug report in to the dev group.
  [Updated consistently in the last 9 years. Last update was in February of this year. I can’t find any record of my bug report, though.]

• VP8 And FFmpeg

  18 juin 2010, par Multimedia Mike — VP8

  UPDATE, 2010-06-17 : You don’t need to struggle through these instructions anymore. libvpx 0.9.1 and FFmpeg 0.6 work together much better. Please see this post for simple instructions on getting up and running quickly.

  Let’s take the VP8 source code (in Google’s new libvpx library) for a spin ; get it to compile and hook it up to FFmpeg. I am hesitant to publish specific instructions for building in the somewhat hackish manner available on day 1 (download FFmpeg at a certain revision and apply a patch) since that kind of post has a tendency to rise in Google rankings. I will just need to remember to update this post after the library patches are applied to the official FFmpeg tree.

  Statement of libvpx’s Relationship to FFmpeg
  I don’t necessarily speak officially for FFmpeg. But I’ve been with the project long enough to explain how certain things work.

  Certainly, some may wonder if FFmpeg will incorporate Google’s newly open sourced libvpx library into FFmpeg. In the near term, FFmpeg will support encoding and decoding VP8 via external library as it does with a number of other libraries (most popularly, libx264). FFmpeg will not adopt the code for its own codebase, even if the license may allow it. That just isn’t how the FFmpeg crew rolls.

  In the longer term, expect the FFmpeg project to develop an independent, interoperable implementation of the VP8 decoder. Sometime after that, there may also be an independent VP8 encoder as well.

  Building libvpx
  Download and build libvpx. This is a basic ’configure && make’ process. The build process creates a static library, a bunch of header files, and 14 utilities. A bunch of these utilities operate on a file format called IVF which is apparently a simple transport method for VP8. I have recorded the file format on the wiki.

  We could use a decoder for this in the FFmpeg code base for testing VP8 in the future. Who’s game ? Just as I was proofreading this post, I saw that David Conrad has sent an IVF demuxer to the ffmpeg-devel list.

  There doesn’t seem to be a ’make install’ step for the library. Instead, go into the overly long directory (on my system, this is generated as vpx-vp8-nopost-nodocs-generic-gnu-v0.9.0), copy the contents of include/ to /usr/local/include and the static library in lib/ to /usr/local/lib .

  Building FFmpeg with libvpx
  Download FFmpeg source code at the revision specified or take your chances with the latest version (as I did). Download and apply provided patches. This part hurts since there is one diff per file. Most of them applied for me.

  Configure FFmpeg with 'configure --enable-libvpx_vp8 --enable-pthreads'. Ideally, this should yield no complaints and ’libvpx_vp8’ should show up in the enabled decoders and encoders sections. The library apparently relies on threading which is why '--enable-pthreads' is necessary. After I did this, I was able to create a new webm/VP8/Vorbis file simply with :

   ffmpeg -i input_file output_file.webm
  

  Unfortunately, I can’t complete the round trip as decoding doesn’t seem to work. Passing the generated .webm file back into FFmpeg results in a bunch of errors of this format :

  [libvpx_vp8 @ 0x8c4ab20]v0.9.0
  [libvpx_vp8 @ 0x8c4ab20]Failed to initialize decoder : Codec does not implement requested capability
  

  Maybe this is the FFmpeg revision mismatch biting me.

  FFmpeg Presets
  FFmpeg features support for preset files which contain collections of tuning options to be loaded into the program. Google provided some presets along with their FFmpeg patches :

  • 1080p50
  • 1080p
  • 360p
  • 720p50
  • 720p

  To invoke one of these (assuming the program has been installed via ’make install’ so that the presets are in the right place) :

   ffmpeg -i input_file -vcodec libvpx_vp8 -vpre 720p output_file.webm
  

  This will use a set of parameters that are known to do well when encoding a 720p video.

  Code Paths
  One of goals with this post was to visualize a call graph after I got the decoder hooked up to FFmpeg. Fortunately, this recon is greatly simplified by libvpx’s simple_decoder utility. Steps :

  • Build libvpx with --enable-gprof
  • Run simple_decoder on an IVF file
  • Get the pl_from_gprof.pl and dot_from_pl.pl scripts frome Graphviz’s gprof filters
  • gprof simple_decoder | ./pl_from_gprof.pl | ./dot_from_pl.pl > 001.dot
  • Remove the 2 [graph] and 1 [node] modifiers from the dot file (they only make the resulting graph very hard to read)
  • dot -Tpng 001.dot > 001.png

  Here are call graphs generated from decoding test vectors 001 and 017.

  
  

  

  Like this, only much larger and scarier (click for full graph)

  
  

  It’s funny to see several functions calling an empty bubble. Probably nothing to worry about. More interesting is the fact that a lot of function_c() functions are called. The ’_c’ at the end is important— that generally indicates that there are (or could be) SIMD-optimized versions. I know this codebase has plenty of assembly. All of the x86 ASM files appear to be written such that they could be compiled with NASM.

  Leftovers
  One interesting item in the code was vpx_scale/leapster. Is this in reference to the Leapster handheld educational gaming unit ? Based on this item from 2005 (archive.org copy), some Leapster titles probably used VP6. This reminds me of finding references to the PlayStation in Duck/On2’s original VpVision source release. I don’t know of any PlayStation games that used Duck’s original codecs but with thousands to choose from, it’s possible that we may find a few some day.