Display DVB subtitles and DVB Teletext from MPEG-TS

Overview

Use this workflow to display or verify a subtitle track already carried by an MPEG transport stream. Open a TS file or a supported network source, list its subtitle tracks, and select the one to display.

To check the output of the Conversion or Generation sample, open the resulting stream at the receiver. Check the expected track and language, then play through a known cue and verify the text appears. For Teletext, select the page used by the sender if automatic selection does not find it.

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. Count subtitle tracks

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. Inspect subtitle track metadata

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 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. Select a Teletext page if needed

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.

So use teletext_page property to select the Teletext subtitle page. If the Teletext subtitles are not detected or decoded by the default reader path, enable the FFmpeg Teletext path with teletext.force_ffmpeg property:

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

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

Reading and writing subtitles

This article is about reading subtitles of a transport stream. The properties file::subtitle_track, teletext_page and teletext.force_ffmpeg belong to the reader. To write subtitles into a transport stream, the writer properties subtitle::codec, subtitle::stream_id and, for DVB Teletext, subtitle::page_number are used, see Insert ASS or SRT subtitles into MPEG-TS and Insert DVB subtitles or DVB Teletext during live output. When you read back a stream that was written with subtitle::page_number, use the same page number for teletext_page.

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Overview

Supported subtitle types

1. Open the source

2. Count subtitle tracks

MPlatform SDK

MFormats SDK

3. Inspect subtitle track metadata

4. Select the track to display

MPlatform SDK

MFormats SDK

5. Select a Teletext page if needed

MPlatform example

MFormats example

Notes

Reading and writing subtitles

See also

Still have questions?

Was this article helpful?

Overview

Supported subtitle types

1. Open the source

2. Count subtitle tracks

MPlatform SDK

MFormats SDK

3. Inspect subtitle track metadata

4. Select the track to display

MPlatform SDK

MFormats SDK

5. Select a Teletext page if needed

MPlatform example

MFormats example

Notes

Reading and writing subtitles

See also

Still have questions?

Was this article helpful?

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