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• Hacking the Popcorn Hour C-200

  3 mai 2010, par Mans — Hardware, MIPS

  Update : A new firmware version has been released since the publication of this article. I do not know if the procedure described below will work with the new version.

  The Popcorn Hour C-200 is a Linux-based media player with impressive specifications. At its heart is a Sigma Designs SMP8643 system on chip with a 667MHz MIPS 74Kf as main CPU, several co-processors, and 512MB of DRAM attached. Gigabit Ethernet, SATA, and USB provide connectivity with the world around it. With a modest $299 on the price tag, the temptation to repurpose the unit as a low-power server or cheap development board is hard to resist. This article shows how such a conversion can be achieved.
  

  Kernel

  The PCH runs a patched Linux 2.6.22.19 kernel. A source tarball is available from the manufacturer. This contains the sources with Sigma support patches, Con Kolivas’ patch set (scheduler tweaks), and assorted unrelated changes. Properly split patches are unfortunately not available. I have created a reduced patch against vanilla 2.6.22.19 with only Sigma-specific changes, available here.

  The installed kernel has a number of features disabled, notably PTY support and oprofile. We will use kexec to load a more friendly one.

  As might be expected, the PCH kernel does not have kexec support enabled. It does however, by virtue of using closed-source components, support module loading. This lets us turn kexec into a module and load it. A patch for this is available here. To build the module, apply the patch to the PCH sources and build using this configuration. This will produce two modules, kexec.ko and mips_kexec.ko. No other products of this build will be needed.

  The replacement kernel can be built from the PCH sources or, if one prefers, from vanilla 2.6.22.19 with the Sigma-only patch. For the latter case, this config provides a minimal starting point suitable for NFS-root.

  When configuring the kernel, make sure CONFIG_TANGOX_IGNORE_CMDLINE is enabled. Otherwise the command line will be overridden by a useless one stored in flash. A good command line can be set with CONFIG_CMDLINE (under “Kernel hacking” in menuconfig) or passed from kexec.

  Taking control

  In order to load our kexec module, we must first gain root privileges on the PCH, and here a few features of the system are working to our advantage :

  1. The PCH allows mounting any NFS export to access media files stored there.
  2. There is an HTTP server running. As root.
  3. This HTTP server can be readily instructed to fetch files from an NFS mount.
  4. Files with a name ending in .cgi are executed. As root.

  All we need do to profit from this is place the kexec modules, the kexec userspace tools, and a simple script on an NFS export. Once this is done, and the mount point configured on the PCH, a simple HTTP request will send the old kernel screaming to /dev/null, our shiny new kernel taking its place.

  The rootfs

  A kernel is mostly useless without a root filesystem containing tools and applications. A number of tools for cross-compiling a full system exist, each with its strengths and weaknesses. The only thing to look out for is the version of kernel headers used (usually a linux-headers package). As we will be running an old kernel, chances are the default version is too recent. Other than this, everything should be by the book.

  Assembling the parts

  Having gathered all the pieces, it is now time to assemble the hack. The following steps are suitable for an NFS-root system. Adaptation to a disk-based system is left as an exercise.

  1. Build a rootfs for MIPS 74Kf little endian. Make sure kernel headers used are no more recent than 2.6.22.x. Include a recent version of the kexec userspace tools.
  2. Fetch and unpack the PCH kernel sources.
  3. Apply the modular kexec patch.
  4. Using this config, build the modules and install them as usual to the rootfs. The version string must be 2.6.22.19-19-4.
  5. From either the same kernel sources or plain 2.6.22.19 with Sigma patches, build a vmlinux and (optionally) modules using this config. Modify the compiled-in command line to point to the correct rootfs. Set the version string to something other than in the previous step.
  6. Copy vmlinux to any directory in the rootfs.
  7. Copy kexec.sh and kexec.cgi to the same directory as vmlinux.
  8. Export the rootfs over NFS with full read/write permissions for the PCH.
  9. Power on the PCH, and update to latest firmware.
  10. Configure an NFS mount of the rootfs.
  11. Navigate to the rootfs in the PCH UI. A directory listing of bin, dev, etc. should be displayed.
  12. On the host system, run the kexec.sh script with the target hostname or IP address as argument.
  13. If all goes well, the new kernel will boot and mount the rootfs.

  Serial console

  A serial console is indispensable for solving boot problems. The PCH board has two UART connectors. We will use the one labeled UART0. The pinout is as follows (not standard PC pinout).

          +-----------+
         2| * * * * * |10
         1| * * * * * |9
          -----------+
            J7 UART0
      /---------------------/ board edge
  

  Pin	Function
  1	+5V
  5	Rx
  6	Tx
  10	GND

  The signals are 3.3V so a converter, e.g. MAX202, is required for connecting this to a PC serial port. The default port settings are 115200 bps 8n1.

• Gstreamer AAC encoding no more supported ?

  22 juillet 2016, par Gianks

  i’d like to include AAC as one of the compatible formats in my app but i’m having troubles with its encoding.
  FAAC seems to be missing in GStreamer-1.0 Debian-derived packages (see Ubuntu) and the main reason for that (if i got it correctly) is the presence of avenc_aac (Lunchpad bugreport) as a replacement.

  I’ve tried the following :

  gst-launch-1.0 filesrc location="src.avi" ! tee name=t  t.! queue ! decodebin ! progressreport ! x264enc ! mux. t.! queue ! decodebin ! audioconvert ! audioresample ! avenc_aac compliance=-2 ! mux. avmux_mpegts name=mux ! filesink location=/tmp/test.avi

  It hangs prerolling with :

  ERROR libav :0:: AAC bitstream not in ADTS format and extradata missing

  Using mpegtsmux instead of avmux_mpegts seems to work since the file is created but it results with no working audio (with some players it’s completely unplayable).

  This is the trace of mplayer :

  Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
  
  [aac @ 0x7f2860d6c3c0]channel element 3.15 is not allocated
  
  [aac @ 0x7f2860d6c3c0]Sample rate index in program config element does not match the sample rate index configured by the container.
  
  [aac @ 0x7f2860d6c3c0]Inconsistent channel configuration.
  
  [aac @ 0x7f2860d6c3c0]get_buffer() failed
  
  [aac @ 0x7f2860d6c3c0]Assuming an incorrectly encoded 7.1 channel layout instead of a spec-compliant 7.1(wide) layout, use -strict 1 to decode according to the specification instead.
  
  [aac @ 0x7f2860d6c3c0]Reserved bit set.
  
  [aac @ 0x7f2860d6c3c0]Number of bands (20) exceeds limit (14).
  
  [aac @ 0x7f2860d6c3c0]invalid band type
  
  [aac @ 0x7f2860d6c3c0]More than one AAC RDB per ADTS frame is not implemented. Update your FFmpeg version to the newest one from Git. If the problem still occurs, it means that your file has a feature which has not been implemented.
  
  [aac @ 0x7f2860d6c3c0]Reserved bit set.
  
  [aac @ 0x7f2860d6c3c0]Number of bands (45) exceeds limit (28).
  
  Unknown/missing audio format -> no sound
  
  ADecoder init failed :(
  
  Opening audio decoder: [faad] AAC (MPEG2/4 Advanced Audio Coding)
  
  FAAD: compressed input bitrate missing, assuming 128kbit/s!
  
  AUDIO: 44100 Hz, 2 ch, floatle, 128.0 kbit/9.07% (ratio: 16000->176400)
  
  Selected audio codec: [faad] afm: faad (FAAD AAC (MPEG-2/MPEG-4 Audio))
  
  ==========================================================================
  
  AO: [pulse] 44100Hz 2ch floatle (4 bytes per sample)
  
  Starting playback...
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Channel coupling not yet implemented, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: Failed to decode frame: Bitstream value not allowed by specification 
  
  Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
  
  VO: [vdpau] 640x480 => 640x480 Planar YV12 
  
  A:3602.2 V:3600.0 A-V:  2.143 ct:  0.000   3/  3 ??% ??% ??,?% 0 0 
  
  FAAD: error: Array index out of range, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Unexpected fill element with SBR data, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Bitstream value not allowed by specification, trying to resync!
  
  FAAD: error: Channel coupling not yet implemented, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: error: PCE shall be the first element in a frame, trying to resync!
  
  FAAD: error: Invalid number of channels, trying to resync!
  
  FAAD: Failed to decode frame: Invalid number of channels 
  
  A:3602.2 V:3600.1 A-V:  2.063 ct:  0.000   4/  4 ??% ??% ??,?% 0 0 

  These the messages produced by VLC (10 seconds of playback) :

  ts info: MPEG-4 descriptor not found for pid 0x42 type 0xf
  
  core error: option sub-original-fps does not exist
  
  subtitle warning: failed to recognize subtitle type
  
  core error: no suitable demux module for `file/subtitle:///tmp//test.avi.idx'
  
  avcodec info: Using NVIDIA VDPAU Driver Shared Library 361.42 Tue Mar 22 17:29:16 PDT 2016 for hardware decoding.
  
  core warning: VoutDisplayEvent 'pictures invalid'
  
  core warning: VoutDisplayEvent 'pictures invalid'
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio warning: ADTS CRC not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: ADTS CRC not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio warning: Invalid ADTS header
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported
  
  packetizer_mpeg4audio error: Multiple blocks per frame in ADTS not supported

  Using the error of the hanging pipeline I’ve finally discovered that avenc_aac should be told in such way to output the data NOT in RAW AAC but in ADTS AAC, the point is that i’ve no idea how to do that with Gstreamer. See here, bottom of the page : FFMPEG Ticket

  At this point since i’ve found no documentation seems right to say we have no support for AAC encoding in GStreamer... which isn’t true, i guess ! (IMHO anyway seems strange the missing of FAAC if AVENC_AAC requires all the time to be set in experimental mode)

  Can someone propose a working pipeline for this ?

  UPDATE

  After some more research i’ve found (via gst-inspect on avenc_aac) what i’m probably looking for but i don’t know how to setup it as needed.
  Have a look at stream-format :

  Pad Templates:
  
    SRC template: 'src'
  
      Availability: Always
  
      Capabilities:
  
        audio/mpeg
  
                 channels: [ 1, 6 ]
  
                     rate: [ 4000, 96000 ]
  
              mpegversion: 4
  
            stream-format: raw
  
          base-profile: lc

  Thanks

• Overthinking My Search Engine Problem

  31 décembre 2013, par Multimedia Mike — General

  I wrote a search engine for my Game Music Appreciation website, because the site would have been significantly less valuable without it (and I would eventually realize that the search feature is probably the most valuable part of this endeavor). I came up with a search solution that was a bit sketchy, but worked… until it didn’t. I thought of a fix but still searched for more robust and modern solutions (where ‘modern’ is defined as something that doesn’t require compiling a C program into a static CGI script and hoping that it works on a server I can’t debug on).

  Finally, I realized that I was overthinking the problem– did you know that a bunch of relational database management systems (RDBMSs) support full text search (FTS) ? Okay, maybe you did, but I didn’t know this.

  Problem Statement
  My goal is to enable users to search the metadata (title, composer, copyright, other tags) attached to various games. To do this, I want to index a series of contrived documents that describe the metadata. 2 examples of these contrived documents, interesting because both of these games have very different titles depending on region, something the search engine needs to account for :

  system : Nintendo NES
  game : Snoopy’s Silly Sports Spectacular
  author : None ; copyright : 1988 Kemco ; dumped by : None
  additional tags : Donald Duck.nsf Donald Duck
  system : Super Nintendo
  
  game : Arcana
  
  author : Jun Ishikawa, Hirokazu Ando ; copyright : 1992 HAL Laboratory ; dumped by : Datschge
  
  additional tags : card.rsn.gamemusic Card Master Cardmaster
  

  The index needs to map these documents to various pieces of game music and the search solution needs to efficiently search these documents and find the various game music entries that match a user’s request.

  Now that I’ve been looking at it for long enough, I’m able to express the problem surprisingly succinctly. If I had understood that much originally, this probably would have been simpler.

  First Solution & Breakage
  My original solution was based on SWISH-E. The CGI script was a C program that statically linked the SWISH-E library into a binary that miraculously ran on my web provider. At least, it ran until it decided to stop working a month ago when I added a new feature unrelated to search. It was a very bizarre problem, the details of which would probably bore you to tears. But if you care, the details are all there in the Stack Overflow question I asked on the matter.

  While no one could think of a direct answer to the problem, I eventually thought of a roundabout fix. The problem seemed to pertain to the static linking. Since I couldn’t count on the relevant SWISH-E library to be on my host’s system, I uploaded the shared library to the same directory as the CGI script and used dlopen()/dlsym() to fetch the functions I needed. It worked again, but I didn’t know for how long.

  Searching For A Hosted Solution
  I know that anything is possible in this day and age ; while my web host is fairly limited, there are lots of solutions for things like this and you can deploy any technology you want, and for reasonable prices. I figured that there must be a hosted solution out there.

  I have long wanted a compelling reason to really dive into Amazon Web Services (AWS) and this sounded like a good opportunity. After all, my script works well enough ; if I could just find a simple Linux box out there where I could install the SWISH-E library and compile the CGI script, I should be good to go. AWS has a free tier and I started investigating this approach. But it seems like a rabbit hole with a lot of moving pieces necessary for such a simple task.

  I had heard that AWS had something in this area. Sure enough, it’s called CloudSearch. However, I’m somewhat discouraged by the fact that it would cost me around $75 per month to run the smallest type of search instance which is at the core of the service.

  Finally, I came to another platform called Heroku. It’s supposed to be super-scalable while having a free tier for hobbyists. I started investigating FTS on Heroku and found this article which recommends using the FTS capabilities of their standard hosted PostgreSQL solution. However, the free tier of Postgres hosting only allows for 10,000 rows of data. Right now, my database has about 5400 rows. I expect it to easily overflow the 10,000 limit as soon as I incorporate the C64 SID music corpus.

  However, this Postgres approach planted a seed.

  RDBMS Revelation
  I have 2 RDBMSs available on my hosting plan– MySQL and SQLite (the former is a separate service while SQLite is built into PHP). I quickly learned that both have FTS capabilities. Since I like using SQLite so much, I elected to leverage its FTS functionality. And it’s just this simple :

  CREATE VIRTUAL TABLE gamemusic_metadata_fts USING fts3
  ( content TEXT, game_id INT, title TEXT ) ;
  SELECT id, title FROM gamemusic_metadata_fts WHERE content MATCH "arcana" ;
  
  479|Arcana
  

  The ‘content’ column gets the metadata pseudo-documents. The SQL gets wrapped up in a little PHP so that it queries this small database and turns the result into JSON. The script is then ready as a drop-in replacement for the previous script.