Configuring encoding

This article explains how to configure encoding by selecting a container format, video/audio codecs, and codec/format attributes.

Encoding Workflow

1. Select a format (container).

2. Select video and audio codecs.

3. Configure codec/format attributes (for example, bitrate).

4. Generate an encoding configuration string.

5. Start encoding.

⚠️ Codecs can only be enumerated after a format is selected, because available codecs depend on the container.

Encoding formats

A format defines the target container (for example, MP4, MKV, MXF) and limits the set of available audio/video codecs to those supported by the selected container.

List available formats

MFormats SDK (MFWriter)

Use WriterOptionGetCount and WriterOptionGetByIndex to enumerate formats.

int count;
m_objWriter.WriterOptionGetCount(eMFWriterOption.eMFWO_Format, out count);

for (int i = 0; i < count; i++)
{
    string shortName, longName;
    m_objWriter.WriterOptionGetByIndex(eMFWriterOption.eMFWO_Format, i, out shortName, out longName);

    // shortName: "mp4"
    // longName:  "MP4 (MPEG-4 Part 14)"
}

WriterOptionGetByIndex returns a short format name (for example, mp4) and a full display name (for example, MP4 (MPEG-4 Part 14)).

MPlatform SDK (MWriter)

Use ConfigGetCount and ConfigGetByIndex to enumerate formats.

int count;
m_objWriter.ConfigGetCount("format", out count);

for (int i = 0; i < count; i++)
{
    string displayName;
    m_objWriter.ConfigGetByIndex("format", i, out displayName);

    // displayName: "MP4 (MPEG-4 Part 14)"
}

ConfigGetByIndex("format", ...) returns the format display name (for example, MP4 (MPEG-4 Part 14)).

Display name vs id (MPlatform)
In MPlatform, a format has:

• display name — used when listing formats (returned by ConfigGetByIndex)

• id — a short internal name (for example, mp4), available via format attributes after calling ConfigSet

Tip: Attribute order is not guaranteed. When you need a specific attribute (like id), query it by name (see examples below).

Set the format

MFormats SDK (MFWriter)

Use WriterOptionSetByIndex to select a format by index. The returned props contains available parameters for that format.

IMFProps props;
m_objWriter.WriterOptionSetByIndex(eMFWriterOption.eMFWO_Format, targetIndex, out props);

MPlatform SDK (MWriter)

Use ConfigSet to select a format. ConfigSet reliably accepts the value returned by ConfigGetByIndex (the display name).

IMAttributes myAttributes;
m_objWriter.ConfigSet("format", "mp4", out myAttributes);

If you need the short internal id (for example, mp4), read it from the returned attributes:

int have;
string idValue;
formatAttrs.AttributesHave("id", out have, out idValue);

if (have != 0)
{
    // idValue == "mp4"
}

Available Video and Audio Codecs

After a format is selected, you can enumerate and set video/audio codecs supported by that format.

List available codecs

MFormats SDK (MFWriter)

// Video codecs
int vCount;
m_objWriter.WriterOptionGetCount(eMFWriterOption.eMFWO_VideoCodec, out vCount);
for (int i = 0; i < vCount; i++)
{
    string shortName, longName;
    m_objWriter.WriterOptionGetByIndex(eMFWriterOption.eMFWO_VideoCodec, i, out shortName, out longName);
}

// Audio codecs
int aCount;
m_objWriter.WriterOptionGetCount(eMFWriterOption.eMFWO_AudioCodec, out aCount);
for (int i = 0; i < aCount; i++)
{
    string shortName, longName;
    m_objWriter.WriterOptionGetByIndex(eMFWriterOption.eMFWO_AudioCodec, i, out shortName, out longName);
}

MPlatform SDK (MWriter)

// Video codecs
int vCount;
m_objWriter.ConfigGetCount("format::video", out vCount);
for (int i = 0; i < vCount; i++)
{
    string codecName;
    m_objWriter.ConfigGetByIndex("format::video", i, out codecName);
}

// Audio codecs
int aCount;
m_objWriter.ConfigGetCount("format::audio", out aCount);
for (int i = 0; i < aCount; i++)
{
    string codecName;
    m_objWriter.ConfigGetByIndex("format::audio", i, out codecName);
}

Set the codecs

MFormats SDK (MFWriter)

IMFProps videoProps;
m_objWriter.WriterOptionSetByIndex(eMFWriterOption.eMFWO_VideoCodec, videoCodecIndex, out videoProps);

IMFProps audioProps;
m_objWriter.WriterOptionSetByIndex(eMFWriterOption.eMFWO_AudioCodec, audioCodecIndex, out audioProps);

MPlatform SDK (MWriter)

IMAttributes videoAttrs;
m_objWriter.ConfigSet("format::video", "mpeg4", out videoAttrs);

IMAttributes audioAttrs;
m_objWriter.ConfigSet("format::audio", "libmp3lame", out audioAttrs);

Setting Attributes

Formats and codecs expose attributes such as bitrate, profiles, GOP settings, or container options (for example, enabling captions).

You can access attributes immediately after selecting a format/codec, or later by requesting the current configuration.

Get current codec attributes

MFormats SDK (MFWriter)

IMFProps videoProps;
string videoName;
m_objWriter.WriterOptionGet(eMFWriterOption.eMFWO_VideoCodec, out videoName, out videoProps);

MPlatform SDK (MWriter)

string videoName;
IMAttributes videoProps;
m_pConfigRoot.ConfigGet("format::video", out videoName, out videoProps)

Enumerate available attributes

MFormats SDK

int nCount = 0;
videoProps.PropsGetCount("", out nCount);
for (int i = 0; i < nCount; i++)
{
    string strName, strValue;
    int isNode;
    videoProps.PropsGetByIndex("", i, out strName, out strValue, out isNode);
}

MPlatform SDK

int nCount = 0;
videoProps.AttributesGetCount(out nCount);
for (int i = 0; i < nCount; i++)
{
    string strName, strValue;
    videoProps.AttributesGetByIndex("", i, out strName, out strValue);
}

Set an attribute

MFormats SDK

videoProps.PropsSet("b", "10M"); // to specify a bitrate

MPlatform SDK

videoProps.AttributesStringSet("b", "10M");

A full list of supported parameters is available in Formats and Codecs.

Using a Ready-to-Use String

Once format, codecs, and attributes are configured, you can obtain a single encoding configuration string and reuse it later.

Get the full configuration string

MFormats SDK

string targetPath, encodingConfig;
m_objWriter.WriterGet(out targetPath, out encodingConfig);

MPlatform SDK

string encodingConfig;
m_objWriter.ConfigGetAll(1, out encodingConfig);

Example result:

format='mp4' video::codec='n264' video::b='10M' audio::codec='aac'

You can save the string to use it as a template later.

Use the configuration string for encoding

MFormats SDK

m_objWriter.WriterSet(@"c:\testEncoding.mp4", 1, "format='mp4' video::codec='mpeg4' video::b='10M' audio::codec='libmp3lame'");

Use 1 in WriterSet to override the previous configuration.

MPlatform SDK

m_objWriter.WriterNameSet(@"c:\testEncoding.mp4", "format='mp4' video::codec='mpeg4' video::b='10M' audio::codec='libmp3lame'");

Validating the Configuration

If the config.auto_check property is enabled, the writer reports an error when an invalid configuration is applied (for example, unsupported or misspelled codec names).

  m_objWriter.PropsSet("config.auto_check", "true");

  m_objWriter.WriterSet(@"c:\testEncoding.mp4", 1, "format='mp4' video::codec='wrongCodecName'
  video::b='10M' audio::codec='libmp3lame'");

This is useful for scenarios such as NVIDIA NVENC encoding, where hardware encoder initialization may fail (for example, due to concurrent session limits). With auto-check enabled, you can detect initialization failures early and fall back to another encoding option.

Encoding Multiple Audio Tracks with Different Codecs

When you enable split_channels, the writer creates multiple audio tracks. You can then assign a different codec to each track.

For example, if the source has 4 channels and you want 2 audio tracks:

• track 0: AAC

• track 1: AC-3

Use:

"format='mp4' split_channels='2' video::codec='mpeg2video' video::b='5M' audio::codec='aac' audio.1::codec='ac3'"

Note: In MFormats SDK, set the _bResetOption parameter of WriterSet to true for this feature to work correctly.

Example (MPlatform): Show current config after user selections

This pattern is useful for UI scenarios: each time the user changes format or codecs, refresh the full config string.

// user selects format
IMAttributes formatAttrs;
writer.ConfigSet("format", selectedFormatDisplayName, out formatAttrs);

// user selects codecs
IMAttributes videoAttrs;
writer.ConfigSet("format::video", selectedVideoCodec, out videoAttrs);

IMAttributes audioAttrs;
writer.ConfigSet("format::audio", selectedAudioCodec, out audioAttrs);

// show resulting config string
string cfg;
writer.ConfigGetAll(1, out cfg);
Console.WriteLine(cfg);