What is Transcoding?
Definition
Transcoding converts media from one codec or format to another by fully decoding the original and re-encoding it into the target - for example, an H.265 MKV video into an H.264 MP4, or a FLAC audio file into MP3.
Transcoding works in two steps: a decoder reads the original stream and turns it back into raw audio or video frames, then an encoder compresses those frames with the target codec and writes them into the chosen container. This is far more CPU-intensive than copying the data, because the content is genuinely re-compressed rather than rewrapped.
Transcoding exists because not every device or platform supports every codec. It lets you make a file playable on a phone, TV, or website, shrink its size, or move to a more efficient codec like H.265 or AV1. Common cases include H.265 to H.264, FLAC to MP3, or a high-bitrate master scaled down to a smaller streaming version.
Transcoding is often confused with remuxing. Remuxing only changes the container (for example MKV to MP4) and is lossless, because the streams are copied untouched. Transcoding re-encodes, so each lossy pass discards a little quality, and repeated transcoding compounds that generation loss.
Quick facts
- Transcoding always re-encodes: it decodes the source, then encodes to the target codec.
- Lossy transcoding loses a small amount of quality on every pass.
- Unlike remuxing, which only swaps the container and is lossless, transcoding rewrites the actual stream.
- It is used to make files compatible, smaller, or switch codecs (e.g. H.265 to H.264, FLAC to MP3).
- It is more CPU-heavy and slower than copying a stream, because every frame is recompressed.