[FFmpeg-user] ffmpeg retry failed segments

[Peter van den Houten]

Hi, reply below.

On 27/09/2023 11:03, Torsten Kaiser wrote:
> Waiting longer might not be helping. What if the first entry is indeed up to 5 seconds long, then immediately switching the source to the next URL? New URL, new TLS-handshake. Browsers do indeed wait longer and retry multiple times to get a lock to the next bit of any web content. Visible to the user by the "hour glass".
>
> But: Knowing the location of the source m3u8 could provide the opportunity to download the playlist itself via [wget <m3u8-url>]. The following link to Wikipedia describes the structure of m3u-files.
>
> https://en.wikipedia.org/wiki/M3U
>
> So it's all plain text. Media entries are local relative links or URLs, so you may want to keep the m3u8's location
>
> Replacing the m3u8-filename with one of the media entries in question (if local append whole path, otherwise replace the whole construct with the URL-entry) should be a valid URL to the media source, provided the issuer allows access without evaluating the http-referer as being of its own realm.
>
> So prepared, try to use ffmpeg with this single media file as input url , watching for errors.
>
> No solution, but trying to circumvent suspected problems with certain entries in the playlist, narrowing down the problem
>
> (And learned for myself what hides behind HLS streaming)
>
> On 27.09.23 09:00, Stein Rune Risa wrote:
>> Hi!
>>
>> This is a very stable and well known source, so the network is also stable.
>> There are never any issues streaming through their official player.
>>
>> I also see that the streams are delivered through well known CDN - so it
>> should be fine.
>>
>> But I will try the xerror option. It is better to detect errors than
>> getting some problem with the file.
>>
>> It also seems that the hiccup always happens within the first 5 seconds of
>> the stream - so there might be some "initial delay" when initializing the
>> stream. Is there some parameter for ffmpeg to kind of allow longer response
>> times from the source?
>>
>>
>>
>> On Wed, Sep 27, 2023 at 8:16 AM Torsten Kaiser <info at linux-rebellen.de>
>> wrote:
>>
>>> Looks like you download a known playlist from some unstable network
>>> connection.
>>>
>>> To get a grasp on this: If you set the -xerror switch like
>>>
>>> ffmpeg -y -xerror -i https://file.com/myfiles.m3u8 -c copy /tmp/test.mkv
>>>
>>> what happens? Download should stop at the first buggy/missing segment of
>>> the playlist. Now repeat the download multiple times to see if the
>>> problem is random or not.
>>>
>>> Missing segments could be a DRM problem or invalid/outdated entries in
>>> the playlist. If the download always misses the same segment it's most
>>> likely the segment entry is invalid.
>>>
>>> Buggy segments are most likely either already buggy in the source or a
>>> network bottleneck. If the faults always occur on the same spot, then
>>> the source itself is most likely already buggy. Encountered this myself
>>> on legacy sources digitized from VHS tapes. Sometimes content is more
>>> important than quality.
>>>
>>>
>>> On 26.09.23 22:36, Stein Rune Risa wrote:
>>>> I am using ffmpeg to download some streaming to a mkv file. The stream parts comes in a m3u8 file.
>>>>
>>>> ffmpeg -y -i https://file.com/myfiles.m3u8 -c copy /tmp/test.mkv
>>>>
>>>> In some cases, there have been some issues downloading some of the segments, and the mkv files have parts where it freezes for some seconds before continuing. I am now forced to check the file manually (by watching) and then redownload if it has any issues.
>>>>
>>>> I guess this happens because ffmpeg temporarily is not able to download some of the segments referred to in the m3u8?
>>>>
>>>> Is there some way that I can force ffmpeg to retry failed segments? Or at least abort if it happens? I am kind of looking for a way to get rid of themanual checking of the content.


As Torsten pointed out, the problem could be DRM or outdated/unavailable segments. I have had no problems using the following code, with a user agent string which keeps the website happy and downloads all segments from most websites, maybe it will help with your instance. This example is to download a copyright-free movie from PlexVideos:

ffmpeg -user_agent "Mozilla/5.0 (iPad; CPU OS 6_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10A5355d Safari/8536.25" -i "https://vod-content.plexvideos.com/streams/62be17835e5872e950b87398/0f59c0e3-59ad-4362-8cf2-11f8508c46f2/stream_6.m3u8" -c copy -y the_brain_that_wouldn't_die.mkv.