In the video, hostage Rudolph Blechschmidt is shown appealing for help, saying that he is in poor health and that his heart medication is running out. The video shows him coughing and speaking with difficulty.
"I ask my friends, my family, my two sons to put more pressure on the German authorities in order to get us free," Blechschmidt says in the video. He says that the German Embassy and Afghan government are trying to negotiate his release, but that "something seems to be going wrong."
Blechschmidt says he is being held with five Afghans who were kidnapped along with him.
The 62-year-old was kidnapped in southern Afghanistan on July 18, a day before a group of 23 South Korean aid workers were abducted in Ghazni Province.
Negotiations for the release of the South Koreans have apparently stalled.
Their Taliban captors are demanding that Kabul release imprisoned militants in exchange for the South Koreans. The militants have killed two of the hostages, and released another two.
The Afghan government has ruled out freeing detained militants in exchange for the hostages' release.