%analyzeNumFinalHiddenFrames% This script is used to examine all files in the current directory and% determine which ones appear to be fully readable.  When completed, it% prints out a table of all videos that appear to be readable, their FourCC% code (essentially it says what codec was used to compress the file), and% an estimate of the number of frames at the end of the file that could not% be read.%% We do this for two reasons... first this lets users know which files can% be accessed.  If a video exists in the current directory but isn't% reported by this script, it's likely that there is either some bug in% videoReader, the codec has not been properly installed, or the file is in% an unsupported format.  %% The second reason for this script deals with what appears to be some% deficiencies in current encoders.  Various encoders seem to create AVI% files such that the last few frames cannot be read.  The rest of this% comment block explains why the encoders are likely to blame.%% As of June 2007, all of the supplied test files were created with the % VirtualDub application (http://www.virtualdub.org).  VirtualDub is a% very mature piece of software with great attention paid to robustness% and correctness, so it is unlikely that the VirtualDub application is% to blame.  As further evidence, other encoder applications yield the% same results when using the same codecs that VirtualDub uses.%% While it's certainly possible that videoReader was implemented % incorrectly, there are reasons to doubt this is the cause.  The same% issues arise when decoding a given vido using the avifile API on % Linux (something we no longer support), the ffmpeg API on Linux, and% the DirectShow API on Windows.  The way of extracting frames from each % of these is quite different (look at FfmpegIVideo::next and % DirectShowIVideo::next if you're curious).  We have also separately% written a test application in DirectShow and were unable to obtain % the last frame's data no matter what we've done.  We also see the same% problems when using the mplayer application to decode the videos.%% Codec bugs?  Given a codec binary, the problems are very repoduceable % with different source files, different encoder applications (except % strangely the revel library produces proper XviD-encoded AVIs but the % XviD Video for Windows codec doesn't), different video lengths, and % different decoder implementations (ffmpeg on Linux, Microsoft's own % DirectShow on Windows, and the mplayer application on Linux).  This % suggest that the problem might actually lie in the codec internals and % our workaround solution that avoids the last few frames may be the % only real solution. %%Examples:%  analyzeNumFinalHiddenFrames%%Copyright (c) 2006 Gerald Dalley%See "MIT.txt" in the installation directory for licensing details (especially%when using this library on GNU/Linux). loadables     = cell(0);fourccs       = cell(0);nHiddenFrames = [];nEst          = [];nFramesActual = [];files = dir('.');for i=1:length(files)  try    % Try opening it    vr = videoReader(files(i).name);        % Can we get basic stream info?    info = getinfo(vr);        % Does it look valid?    if (info.width     <= 0), error('bad width');     end    if (info.height    <= 0), error('bad height');    end    if (info.bpp       <= 0), error('bad bpp');       end    if (info.numFrames <= 0), error('bad numFrames'); end        if isfield(info, 'nHiddenFinalFrames')      nEst(end+1) = info.nHiddenFinalFrames; %#ok<AGROW> (there aren't that many files and we don't know how many errors will occur above this)    else      nEst(end+1) = nan; %#ok<AGROW>    end        % Can we read the first frame?    if (~next(vr)), error('first next call failed'); end        % Is it at least the right size?    frame = getframe(vr);    if (~all(size(frame) == [info.height info.width info.bpp/8])),       error('returned frame is the wrong size');     end        % Undo nHiddenFinalFrames so we can really test how many frames there    % are.  The videoReader plugins will all let us attempt to read at    % least info.numFrames + info.nHiddenFinalFrames frames.    info.numFrames = info.numFrames + info.nHiddenFinalFrames;        % Can we actually read every frame?    hFrames = info.numFrames - 1;    for fnum=2:info.numFrames      try        if (~next(vr)), break; end        hFrames = hFrames - 1;      catch        break      end    end    % Close it since we're done with it for now.    vr = close(vr);        % It looks good, so squirrel the name away    loadables{end+1} = files(i).name; %#ok<AGROW>    if (isempty(info.fourcc)), info.fourcc = '    '; end % for formatting    fourccs{end+1} = info.fourcc; %#ok<AGROW>    nHiddenFrames(end+1) = hFrames; %#ok<AGROW>    nFramesActual(end+1) = info.numFrames - hFrames; %#ok<AGROW>  catch  endendfprintf('\n\n');fprintf('# actual  nHiddenFrames    fcc     file\n');fprintf('  frames     est actual    code    name\n');fprintf('--------  ------ ------    ----   -----\n');for i=1:length(loadables)  fprintf('% 8d % 7d % 6d    %s   %s\n', ...          nFramesActual(i), nEst(i), nHiddenFrames(i), fourccs{i}, ...          loadables{i});end