Displaying DVB subtitles/teletext from transport stream

Overview

You can display DVB subtitles and DVB Teletext subtitles from a transport stream source, such as a TS file, DVB stream, UDP stream, or another supported MPEG-TS input, by using MPlatform SDK or MFormats SDK.

The general workflow is:

1. Open the source with MFile in MPlatform SDK or MFReader in MFormats SDK.
2. Check how many subtitle tracks are available.
3. Get detailed information about the subtitle tracks, if needed.
4. Select the subtitle track to display.
5. For DVB Teletext subtitles, configure the Teletext page and FFmpeg Teletext reader options when required.
6. Start playback or frame processing.

Supported subtitle types

The SDK can display subtitle tracks available in the source transport stream, including:

• DVB subtitles — bitmap-based subtitles.
• DVB Teletext subtitles — Teletext subtitle pages, commonly page 888.

The available subtitle tracks and their metadata can be inspected through source information properties.

1. Open the source

In MPlatform SDK, use MFile.

MFileClass file = new MFileClass();

file.FileNameSet(sourcePath, "");

In MFormats SDK, use MFReader.

MFReaderClass reader = new MFReaderClass();

reader.ReaderOpen(sourcePath, "");

2. Check if subtitle tracks are available

To check whether the source contains subtitle tracks, read the file::info::subtitle_tracks property with PropsGet.

MPlatform SDK

string tracksNumber = "";
file.PropsGet("file::info::subtitle_tracks", out tracksNumber);

Console.WriteLine($"Subtitle tracks: {tracksNumber}");

MFormats SDK

string tracksNumber = "";
reader.PropsGet("file::info::subtitle_tracks", out tracksNumber);

Console.WriteLine($"Subtitle tracks: {tracksNumber}");

If the returned value is 0 or empty, the source does not expose subtitle tracks through this property.

3. Get subtitle track information

Each subtitle track can expose additional information through indexed properties. Track indexes are zero-based.

For example, to get the codec name for subtitle track 0:

string subtitleCodecName = "";
file.PropsGet("file::info::subtitle.0::codec_name", out subtitleCodecName);

Console.WriteLine($"Subtitle codec: {subtitleCodecName}");

The same property can be used with MFReader in MFormats SDK:

string subtitleCodecName = "";
reader.PropsGet("file::info::subtitle.0::codec_name", out subtitleCodecName);

Console.WriteLine($"Subtitle codec: {subtitleCodecName}");

Common subtitle information properties are:

• file::info::subtitle.0::idx — subtitle stream index.
• file::info::subtitle.0::codec_name — subtitle codec name.
• file::info::subtitle.0::time_base — subtitle time base.
• file::info::subtitle.0::start_time — subtitle start time.
• file::info::subtitle.0::duration — subtitle duration.

Replace 0 with the required subtitle track number to inspect other subtitle tracks. For example:

file::info::subtitle.1::codec_name
file::info::subtitle.2::codec_name

4. Select the subtitle track to display

To display subtitles, set the subtitle track index with file::subtitle_track.

For example, to select subtitle track 0:

MPlatform SDK

file.PropsSet("file::subtitle_track", "0");

MFormats SDK

reader.PropsSet("file::subtitle_track", "0");

After the track is selected, start playback or frame processing as usual. The selected subtitle track is rendered together with the video output.

5. DVB Teletext subtitle specifics

DVB Teletext subtitles may require additional Teletext options. In many broadcasts, Teletext subtitles are stored on page 888, but the actual page can be different depending on the source.

Use teletext_page to select the Teletext subtitle page:

file.PropsSet("teletext_page", "888");

For MFormats SDK:

reader.PropsSet("teletext_page", "888");

If the Teletext subtitles are not detected or decoded by the default reader path, enable the FFmpeg Teletext path with teletext.force_ffmpeg.

Runtime properties

file.PropsSet("teletext.force_ffmpeg", "true");
file.PropsSet("teletext_page", "888");

For MFormats SDK:

reader.PropsSet("teletext.force_ffmpeg", "true");
reader.PropsSet("teletext_page", "888");

These options can also be stored in the registry for the reader component.

MFormats registry options

Computer\HKEY_CURRENT_USER\SOFTWARE\Medialooks\MFormats\MFReader
teletext.force_ffmpeg = true
teletext_page = 888

If these registry values do not exist, create them manually. The default Teletext subtitle page is usually 888, but you should use the page number required by the source stream.

MPlatform example

The following example opens a transport stream source, checks available subtitle tracks, selects the first subtitle track, and starts playback.

using System;
using System.Runtime.InteropServices;
using MPLATFORMLib;

public static class DvbSubtitlePlaybackMPlatform
{
    public static void PlayWithSubtitles(string sourcePath)
    {
        MFileClass file = null;

        try
        {
            file = new MFileClass();

            file.FileNameSet(sourcePath, "");

            string tracksNumber = "";
            file.PropsGet("file::info::subtitle_tracks", out tracksNumber);

            Console.WriteLine($"Subtitle tracks: {tracksNumber}");

            string subtitleCodecName = "";
            file.PropsGet("file::info::subtitle.0::codec_name", out subtitleCodecName);

            Console.WriteLine($"Subtitle track 0 codec: {subtitleCodecName}");

            file.PropsSet("file::subtitle_track", "0");

            // Use these options for DVB Teletext subtitles when needed.
            file.PropsSet("teletext.force_ffmpeg", "true");
            file.PropsSet("teletext_page", "888");

            file.FilePlayStart();

            // Keep the application running while playback is active.
        }
        finally
        {
            if (file != null)
                Marshal.ReleaseComObject(file);
        }
    }
}

MFormats example

The following example opens a transport stream source, checks available subtitle tracks, selects the first subtitle track, and reads frames.

using System;
using System.Runtime.InteropServices;
using MFORMATSLib;

public static class DvbSubtitlePlaybackMFormats
{
    public static void ReadFramesWithSubtitles(string sourcePath)
    {
        MFReaderClass reader = null;

        try
        {
            reader = new MFReaderClass();

            reader.ReaderOpen(sourcePath, "");

            string tracksNumber = "";
            reader.PropsGet("file::info::subtitle_tracks", out tracksNumber);

            Console.WriteLine($"Subtitle tracks: {tracksNumber}");

            string subtitleCodecName = "";
            reader.PropsGet("file::info::subtitle.0::codec_name", out subtitleCodecName);

            Console.WriteLine($"Subtitle track 0 codec: {subtitleCodecName}");

            reader.PropsSet("file::subtitle_track", "0");

            // Use these options for DVB Teletext subtitles when needed.
            reader.PropsSet("teletext.force_ffmpeg", "true");
            reader.PropsSet("teletext_page", "888");

            while (true)
            {
                MFFrame frame = null;

                try
                {
                    ((IMFSource)reader).SourceFrameGet(-1, out frame, "");

                    if (frame == null)
                        break;

                    // Process or preview the frame here.
                }
                finally
                {
                    if (frame != null)
                        Marshal.ReleaseComObject(frame);
                }
            }

            reader.ReaderClose();
        }
        finally
        {
            if (reader != null)
                Marshal.ReleaseComObject(reader);
        }
    }
}

Notes

• Use file::info::subtitle_tracks to check how many subtitle tracks are available.
• Use file::info::subtitle.N::codec_name and related properties to inspect a specific subtitle track.
• Use file::subtitle_track to select the subtitle track to display.
• For DVB Teletext subtitles, use teletext_page to select the required page.
• If Teletext subtitles are not detected by the default reader path, use teletext.force_ffmpeg=true.
• Page 888 is a common Teletext subtitle page, but the correct page depends on the source stream.