feldspar-mpeg1-decoder

A partially complete MPEG-1 video decoder written in Feldspar as a Master's Thesis in computer science at Chalmers University of Technology. It should be seen as a proof of concept rather than a usable decoder.

Compliance and limitations

The decoder can decode MPEG-1 video files with the following limitations (and possibly more):

• The input must be a raw MPEG-1 video stream (not inside any container)
• The stream may only contain I- and P-frames (B- and D-frames are not supported)
• The horizontal resolution must be a multiple of 16.

Usage limitaions of the decoder:

• As Feldspar doesn't support command line arguments nor string manipulation, the input file names must be supplied to the Haskell main function or hardcoded in Main.hs (see the usage section). This also means that Feldspar has to generate the C source code and compile it every time the input file name is changed.
• The output file format is YV12 as described here
• The output file name is ../v.yuv unless modified in Main.hs
• The decoder does not recover from any errors in the input and crashes even upon successfully completing the decoding process.

Usage

The following should sucessfully download and build the decoder along with the required libraries:

$ git clone https://github.com/mightynerd/feldspar-mpeg1-decoder
$ cd feldspar-mpeg1-decoder
$ stack build

NOTE: You may have to add allow-newer: true to your global stack config because of our quirky config, usually located in ~/.stack/stack.yaml

Once this has completed, you can use stack run to run the decoder:

$ stack run -- "INPUT_FILE" run

Where the first argument is the input MPEG-1 video file. The second argument may be:

• run which generates the C code, compiles it and decodes the input file.
• compile which only outputs the generated C code to stdout.

Creating input files

To create a input file, use ffmpeg as follows:

$ ffmpeg -i INPUT_FILE -f mpeg1video OUTPUT_FILE

This will work for any ÌNPUT_FILE that your ffmpeg version supports. Note that the decoder is very slow and you might want to rescale it to a lower resolution using the -s argument, such as -s 640x360.

Playing back the output files

The output files can be played back with ffplay in the following way:

$ ffplay -s WIDTHxHEIGHT FILE_NAME

Remember to specify the resolution of the video as the raw output file does not contain this information.

The equivalent but with mplayer:

$ mplayer -demuxer rawvideo -rawvideo w=640:h=360:format=i420 FILE_NAME

Generating VLC trees and matrices

The VLC trees and matrices required for the decoding process are stored in their respective folders in plain text format. Their corresponding Haskell representation can be generated using GenerateVLC.hs and GenerateMatrices.hs.