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This is the code related blog of John Dyer. I develop web applications in ASP.NET, Flash, and JavaScript for Dallas Theological Seminary and personally as Refresh Development, Inc.

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Flash FLV meta reader in .NET (C#)

by John Dyer

I am doing a lot of work with Flash MX and video (flv) and I recently needed to get the duration off of a bunch of FLV files. Sorensen now correctly adds the duration, width, height, framerate, creation date, and the audio and video data rates. I wrote some C# code to read and parse this information off the file.

using System.IO;
namespace Refresh.FlashTools
{
    /// <summary>
    /// Reads the meta information embedded in an FLV file
    /// </summary>
    public class FlvMetaDataReader
    {
        /// <summary>
        /// Reads the meta information (if present) in an FLV
        /// </summary>
        /// <param name="path">The path to the FLV file</returns>
        public static FlvMetaInfo GetFlvMetaInfo(string path)
        {
            if (!File.Exists(path))
            {
                throw new Exception(String.Format("File '{0}' doesn't exist for FlvMetaDataReader.GetFlvMetaInfo(path)", path));
            }
            bool hasMetaData = false;
            double duration = 0;
            double width = 0;
            double height = 0;
            double videoDataRate = 0;
            double audioDataRate = 0;
            Double frameRate = 0;
            DateTime creationDate = DateTime.MinValue;
            // open file 
            FileStream fileStream = new FileStream(path, FileMode.Open);
            try
            {
                // read where "onMetaData"
                byte[] bytes = new byte[10];
                fileStream.Seek(27, SeekOrigin.Begin);
                int result = fileStream.Read(bytes, 0, 10);
                // if "onMetaData" exists then proceed to read the attributes
                string onMetaData = ByteArrayToString(bytes);
                if (onMetaData == "onMetaData")
                {
                    hasMetaData = true;
                    // 16 bytes past "onMetaData" is the data for "duration" 
                    duration = GetNextDouble(fileStream, 16, 8);
                    // 8 bytes past "duration" is the data for "width"
                    width = GetNextDouble(fileStream, 8, 8);
                    // 9 bytes past "width" is the data for "height"
                    height = GetNextDouble(fileStream, 9, 8);
                    // 16 bytes past "height" is the data for "videoDataRate"
                    videoDataRate = GetNextDouble(fileStream, 16, 8);
                    // 16 bytes past "videoDataRate" is the data for "audioDataRate"
                    audioDataRate = GetNextDouble(fileStream, 16, 8);
                    // 12 bytes past "audioDataRate" is the data for "frameRate"
                    frameRate = GetNextDouble(fileStream, 12, 8);
                    // read in bytes for creationDate manually
                    fileStream.Seek(17, SeekOrigin.Current);
                    byte[] seekBytes = new byte[24];
                    result = fileStream.Read(seekBytes, 0, 24);
                    string dateString = ByteArrayToString(seekBytes);
                    // create .NET readable date string
                    // cut off Day of Week
                    dateString = dateString.Substring(4);
                    // grab 1) month and day, 2) year, 3) time
                    dateString = dateString.Substring(0, 6) + " " + dateString.Substring(16, 4) + " " + dateString.Substring(7, 8);
                    // .NET 2.0 has DateTime.TryParse
                    try
                    {
                        creationDate = Convert.ToDateTime(dateString);
                    }
                    catch { }
                }
            }
            catch (Exception e)
            {
                // no error handling
            }
            finally
            {
                fileStream.Close();
            }
            return new FlvMetaInfo(hasMetaData, duration, width, height, videoDataRate, audioDataRate, frameRate, creationDate);
        }
        private static Double GetNextDouble(FileStream fileStream, int offset, int length)
        {
            // move the desired number of places in the array
            fileStream.Seek(offset, SeekOrigin.Current);
            // create byte array
            byte[] bytes = new byte[length];
            // read bytes
            int result = fileStream.Read(bytes, 0, length);
            // convert to double (all flass values are written in reverse order)
            return ByteArrayToDouble(bytes, true);
        }
        private static string ByteArrayToString(byte[] bytes)
        {
            string byteString = string.Empty;
            foreach (byte b in bytes)
            {
                byteString += Convert.ToChar(b).ToString();
            }
            return byteString;
        }
        private static Double ByteArrayToDouble(byte[] bytes, bool readInReverse)
        {
            if (bytes.Length != 8)
                throw new Exception("bytes must be exactly 8 in Length");
            if (readInReverse)
                Array.Reverse(bytes);
            return BitConverter.ToDouble(bytes, 0);
        }
    }
    /// <summary>
    /// Read only container holding meta data embedded in FLV files
    /// </summary>
    public class FlvMetaInfo
    {
        private Double _duration;
        private Double _width;
        private Double _height;
        private Double _frameRate;
        private Double _videoDataRate;
        private Double _audioDataRate;
        private DateTime _creationDate;
        private bool _hasMetaData;
        /// <summary>
        /// The duration in seconds of the video
        /// </summary>
        public Double Duration
        {
            get { return _duration; }
            //set { _duration = value; }
        }
        /// <summary>
        /// The width in pixels of the video
        /// </summary>
        public Double Width
        {
            get { return _width; }
            //set { _width = value; }
        }
        /// <summary>
        /// The height in pixels of the video
        /// </summary>
        public Double Height
        {
            get { return _height; }
            //set { _height = value; }
        }
        /// <summary>
        /// The data rate in KB/sec of the video 
        /// </summary>
        public Double VideoDataRate
        {
            get { return _videoDataRate; }
            //set { _videoDataRate = value; }
        }
        /// <summary>
        /// The data rate in KB/sec of the video's audio track
        /// </summary>
        public Double AudioDataRate
        {
            get { return _audioDataRate; }
            //set { _audioDataRate = value; }
        }
        /// <summary>
        /// The frame rate of the video
        /// </summary>
        public Double FrameRate
        {
            get { return _frameRate; }
            //set { _frameRate = value; }
        }
        /// <summary>
        /// The creation date of the video
        /// </summary>
        public DateTime CreationDate
        {
            get { return _creationDate; }
            //set { _creationDate = value; }
        }
        /// <summary>
        /// Whether or not the FLV has meta data
        /// </summary>
        public bool HasMetaData
        {
            get { return _hasMetaData; }
            //set { _hasMetaData = value; }
        }
        internal FlvMetaInfo(bool hasMetaData, Double duration, Double width, Double height, Double videoDataRate, Double audioDataRate, Double frameRate, DateTime creationDate)
        {
            _hasMetaData = hasMetaData;
            _duration = duration;
            _width = width;
            _height = height;
            _videoDataRate = videoDataRate;
            _audioDataRate = audioDataRate;
            _frameRate = frameRate;
            _creationDate = creationDate;
        }
    }
}

Update: Dave Daku converted this to VB:

Imports System.IO
Namespace Refresh.FlashTools
  '
  ' Returns the meta information embedded in an FLV file
  ' Written in C# by John Dyer: http://johndyer.name/post/2005/08/Flash-FLV-meta-reader-in-NET-(C).aspx
  ' Conversion to VB.net by Dave Daku (11/29/2007)
  '
  Public Class flvMetaDataReader
     Public Shared Function getFlvMetaInfo(ByRef path As String) As flvMetaInfo
        If (Not File.Exists(path)) Then
           Throw New Exception(String.Format("File '{0}' doesn't exist for flvMetaDataReader.getFlvMetaInfo(path)", path))
        End If
        Dim hasMetaData As Boolean = False
        Dim duration As Double = 0
        Dim width As Double = 0
        Dim height As Double = 0
        Dim videoDataRate As Double = 0
        Dim audioDataRate As Double = 0
        Dim frameRate As Double = 0
        Dim creationDate As DateTime = DateTime.MinValue
        ' open the file
        Dim fileStream As FileStream = New FileStream(path, FileMode.Open)
        Try
           ' read where "onMetaData"
           Dim bytes As Byte() = New Byte(10) {}
           fileStream.Seek(27, SeekOrigin.Begin)
           Dim result As Integer = fileStream.Read(bytes, 0, 10)
           ' if "onMetaData" exists then proceed to read the attributes
           Dim onMetaData As String = byteArrayToString(bytes)
           If (onMetaData = "onMetaData") Then
              hasMetaData = True
              ' 16 bytes past "onMetaData" is the data for "duration"
              duration = getNextDouble(fileStream, 16, 8)
              ' 8 bytes past "duration" is the data for "width"
              width = getNextDouble(fileStream, 8, 8)
              ' 9 bytes past "width" is the data for "height"
              height = getNextDouble(fileStream, 9, 8)
              ' 16 bytes past "height" is the data for "videoDataRate"
              videoDataRate = getNextDouble(fileStream, 16, 8)
              ' 16 bytes past "videoDataRate" is the data for "audioDataRate"
              audioDataRate = getNextDouble(fileStream, 16, 8)
              ' 12 bytes past "audioDataRate" is the data for "frameRate"
              frameRate = getNextDouble(fileStream, 12, 8)
              ' read in bytes for creationDate manually
              fileStream.Seek(17, SeekOrigin.Current)
              Dim seekBytes As Byte() = New Byte(24) {}
              result = fileStream.Read(seekBytes, 0, 24)
              Dim dateString As String = byteArrayToString(seekBytes)
              ' create .NET readable date string
              ' cut off Day of Week
              dateString = dateString.Substring(4)
              ' grab 1) month and day, 2) year, 3) time
              dateString = dateString.Substring(0, 6) + " " + dateString.Substring(16, 4) + " " + dateString.Substring(7, 8)
              ' .NET 2.0 has dateTime.tryParse
              Try
                 Date.TryParse(dateString, creationDate)
              Catch ex As Exception
                 Try
                    creationDate = CDate(dateString)
                 Catch ex2 As Exception
                 End Try
              End Try
           End If
        Catch ex As Exception
           ' no error handling
        Finally
           fileStream.Close()
        End Try
        Return New flvMetaInfo(hasMetaData, duration, width, height, videoDataRate, audioDataRate, frameRate, creationDate)
     End Function
     Private Shared Function getNextDouble(ByVal fileStream As
FileStream, ByVal offset As Integer, ByVal length As Integer) As Double
        ' move the desired number of places in the array
        fileStream.Seek(offset, SeekOrigin.Current)
        ' create byte array
        Dim bytes As Byte() = New Byte(length) {}
        ' read bytes
        Dim result As Integer = fileStream.Read(bytes, 0, length)
        ' convert to double (all flash values are written in reverse orer)
        Return byteArrayToDouble(bytes, True)
     End Function
     Private Shared Function byteArrayToString(ByRef bytes() As Byte) As String
        Dim byteString As String = String.Empty
        For Each b As Byte In bytes
           byteString += Convert.ToChar(b).ToString()
        Next
        Return byteString
     End Function
     Private Shared Function byteArrayToDouble(ByRef bytes As Byte(), ByVal readInReverse As Boolean) As Double
        If (bytes.Length <> 8) Then
           Throw New Exception("Bytes must be exactly 8 in length")
        End If
        If (readInReverse) Then
           Array.Reverse(bytes)
        End If
        Return BitConverter.ToDouble(bytes, 0)
     End Function
  End Class
  ' Read-only container for holding meta data embedded in FLV files
  Public Class flvMetaInfo
     Private _duration As Double
     Private _width As Double
     Private _height As Double
     Private _frameRate As Double
     Private _videoDataRate As Double
     Private _audioDataRate As Double
     Private _creationDate As DateTime
     Private _hasMetaData As Boolean
     ' The duration in seconds of the video
     Public ReadOnly Property duration() As Double
        Get
           Return _duration
        End Get
     End Property
     ' The width in pixels of the video
     Public ReadOnly Property width() As Double
        Get
           Return _width
        End Get
     End Property
     ' The height in pixels of the video
     Public ReadOnly Property height() As Double
        Get
           Return _height
        End Get
     End Property
     ' the data rate in KB/sec of the video
     Public ReadOnly Property videoDataRate() As Double
        Get
           Return _videoDataRate
        End Get
     End Property
     ' the data rate in KB/sec of the video's audio track
     Public ReadOnly Property audioDataRate() As Double
        Get
           Return _audioDataRate
        End Get
     End Property
     ' the frame rate of the video
     Public ReadOnly Property frameRate() As Double
        Get
           Return _frameRate
        End Get
     End Property
     ' the creation date of the video
     Public ReadOnly Property creationDate() As DateTime
        Get
           Return _creationDate
        End Get
     End Property
     ' the frame rate of the video
     Public ReadOnly Property hasMetaData() As Boolean
        Get
           Return _hasMetaData
        End Get
     End Property
     Public Sub New(ByVal hasMetaData As Boolean, ByVal duration As
Double, ByVal width As Double, ByVal height As Double, ByVal
videoDataRate As Double, ByVal audioDataRate As Double, ByVal frameRate
As Double, ByVal creationDate As DateTime)
        _hasMetaData = hasMetaData
        _duration = duration
        _width = width
        _height = height
        _videoDataRate = videoDataRate
        _audioDataRate = audioDataRate
        _frameRate = frameRate
        _creationDate = creationDate
     End Sub
  End Class
End Namespace

I'd like to also be able to get the duration off the FLV if the meta data did not get inserted, but the best solution I found (FLV MetaData Injector) is not open source.

Tags: flv, C#, flash, meta
Categories: Code Lab | Flash

Permalink | Comments (20) | Post RSS RSS comment feed

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Comments

March 13. 2008 02:42

many Thanks. This saved my time a lot

Geeshan

March 27. 2008 18:43

it doesn't pull the duration properly for me... seems to want to pull a decimal value of 9.8732 or something instead of the actual 48 seconds... why??

shawn livermore

March 28. 2008 11:25

@shawn, it could be that the meta data for your FLV is somehow incorrect. You can check it with http://www.buraks.com/flvmdi/

John Dyer

April 9. 2008 01:52

Thanks alot for this class.

setareh

June 6. 2008 09:38

Hi, I am looking to embed a flash action script in a c# application. However once the objects are layed out can the flash object be saved so that the user can view that flash object each time?

Assistance in this regard will be appreciated

Sameer Parker

June 17. 2008 15:03

Either bad conversion or bad code.
In getNextDouble, array of Byte was dimmed incorrectly.

Correct line should read:
Dim bytes As Byte() = New Byte(length - 1) {}

Jason Vetter

June 24. 2008 08:16

First of all thanks for this article! Although I needed to tweak some code, this sure put me on the right track.
Concerning Shawns remark on the odd decimal values for duration - I had the same problem getting the correct width and height values from the header. Even after using the tools from http://www.buraks.com/flvmdi/ I kept getting bizarre results. It turned out that the parameter/value pairs are not always on the same offset in the headers, and in some cases (Youtube!) width and height are not available at all.
Eventually I changed the code, I dump the header in a string and use string.IndexOf to determine the offset value for the needed parameter. Works like a charm.

Thanks, Herman

Herman

July 21. 2008 21:11

If anyone's interested, here is some code to extract duration if metadata is missing. It's modeled after code found at http://flixforums.com/archive/index.php/t-149.html

Public Function getFLVDuration(ByVal flv As String) As Double
If File.Exists(flv) Then
Dim flvFile As New FileStream(flv, FileMode.Open, FileAccess.Read, FileShare.Read)
flvFile.Position = flvFile.Length - 4
Using br As New BinaryReader(flvFile)
'-- set Byte Array to length four array from end of file
Dim offsetHEX32 As Byte() = br.ReadBytes(4)

'-- Convert to Little Endian Byte Array for BitConverter
Array.Reverse(offsetHEX32)

'-- Convert to Int32 as offset to find last timestamp tag in FLV
Dim offset As Int32 = BitConverter.ToInt32(offsetHEX32, 0)

flvFile.Position = flvFile.Length - (offset)
Dim durationHEX32 As Byte()

'-- Read in three Byte duration
durationHEX32 = br.ReadBytes(3)

'-- Convert to Little Endian Byte Array for BitConverter
Array.Reverse(durationHEX32)

'-- Pad to 32 bits for conversion
ReDim Preserve durationHEX32(3)
durationHEX32(3) = 0 '-- this actually redundant, default is zero

'-- Convert Byte Array to FLV duration in ms
Dim durationms As Int32 = BitConverter.ToInt32(durationHEX32, 0)

'-- Return in seconds
Return durationms / 1000
End Using
End If
End Function

Colin

July 21. 2008 21:12

Oh and the above code is VB.NET. Sorry for the addendum.

Colin

July 30. 2008 08:36

hi,

vb.net version doesnt appear to work - even with suggested ammendment .... i get no metedata - if i switxh to C# - all is revealed - using same flv ...... can u advise ? thanks

Nazimba

July 30. 2008 09:18

@Nazimba, sorry I didn't write the VB version. It was submitted by another user. If you are set on using VB perhaps you could compare the two and contribute your fixed code...

John Dyer

August 15. 2008 08:56

I have tried your class and on first look it works ok, but then I've stumbled upon a flv file from which the class would read really strange values. In the header the onMetaData field is present, but then there is data in the format (As far as I can see) [length][string of specified length(ex:"framerate")][some binary data] then it repeats itself.

Do you have an update for this class by any chance?
Siderite's last post: Serializing objects in .Net

Siderite

October 30. 2008 08:07

I'd like to suggest changing line "32" to:
FileStream fileStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
... that prevents two process from competing for file access. For example: IIS, PDF creator and your class.

Anton

December 9. 2008 19:08

Great work, very helpful. Thank you,

Kenny DellaValle

December 19. 2008 16:37

Hi,

I am getting video height in Double value format. How to convert it into pixel format?

Thank You,

JavaDeveloper

December 22. 2008 09:18

Hi,

Whenever I tries to run this program by passing FLV file as input. I am getting height = 1.76797281436801E-205 and width = 2.86533732650716E+161

I have checked with http://www.buraks.com/flvmdi/ tool by passing same FLV and it is giving me the correct result like height = 320 px and width = 420 px

Can you please suggest / comments on this to solve this issues.

Jd

December 22. 2008 18:00

Jd, it's been a few years since I've looked at this. If you're familiar with C# you could walk through the code and see if your FLV is formatted differently.

John Dyer

December 24. 2008 01:43

Yes. my flv file is formatted properly otherwise how http://www.buraks.com/flvmdi/ tool is giving me the correct result?

Any hint?

Thanks,
Jd

JavaDeveloper

January 1. 2009 13:52

@Colin: Your code did the trick for me for extracting FLV duration, here is C# conversion I did:

public static double GetFLVDuration( string filename )
{
if( !File.Exists( filename ) ) return 0;
try
{
int duration = 0;
FileStream fs = new FileStream( filename, FileMode.Open, FileAccess.Read, FileShare.Read );
fs.Position = fs.Length - 4;
using( BinaryReader br = new BinaryReader( fs ) )
{
byte[] hex = br.ReadBytes( 4 );
int offset = hex[3] + (hex[2] << 8) + (hex[1] << 16) + (hex[0] << 24);
fs.Position = fs.Length - offset;
hex = br.ReadBytes( 3 );
duration = hex[2] + (hex[1] << 8) + (hex[0] << 16);
}
fs.Close();
fs.Dispose();
return duration / 1000.0;
} catch( Exception )
{
return 0;
}
}

Vex

January 3. 2009 01:23

hi,

i want to extract the iframes and write to a file form the transport stream file .plz explain me step by step how to do this.

asha

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Flash FLV meta reader in .NET (C#)

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