[FFmpeg-devel] [PATCH v2] ffmpeg: Add option to force a specific decode format

Mark Thompson sw at jkqxz.net
Wed Nov 14 03:10:53 EET 2018


On 14/11/18 00:50, Fu, Linjie wrote:
>> -----Original Message-----
>> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
>> Of Mark Thompson
>> Sent: Wednesday, November 14, 2018 07:44
>> To: ffmpeg-devel at ffmpeg.org
>> Subject: [FFmpeg-devel] [PATCH v2] ffmpeg: Add option to force a specific
>> decode format
>>
>> Fixes #7519.
>> ---
>>  doc/ffmpeg.texi      | 13 ++++++++++++
>>  fftools/ffmpeg.c     | 10 ++++++++++
>>  fftools/ffmpeg.h     |  4 ++++
>>  fftools/ffmpeg_opt.c | 47
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  4 files changed, 74 insertions(+)
>>
>> diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
>> index 3717f22d42..d127bc0f0d 100644
>> --- a/doc/ffmpeg.texi
>> +++ b/doc/ffmpeg.texi
>> @@ -920,6 +920,19 @@ would be more efficient.
>>  When doing stream copy, copy also non-key frames found at the
>>  beginning.
>>
>> + at item -decode_format[:@var{stream_specifier}]
>> @var{pixfmt}[, at var{pixfmt}...] (@emph{input,per-stream})
>> +Set the possible output formats to be used by the decoder for this stream.
>> +If the decoder does not natively support any format in the given list for
>> +the input stream then decoding will fail rather than continuing with a
>> +different format.
>> +
>> +In general this should not be set - the decoder will select an output
>> +format based on the input stream parameters and available components,
>> and
>> +that will be automatically converted to whatever the output requires.  It
>> +may be useful to force a hardware decoder supporting output in multiple
>> +different memory types to pick a desired one, or to ensure that a hardware
>> +decoder is used when software fallback is also available.
>> +
>>  @item -init_hw_device
>> @var{type}[=@var{name}][:@var{device}[, at var{key=value}...]]
>>  Initialise a new hardware device of type @var{type} called @var{name},
>> using the
>>  given device parameters.
>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
>> index 38c21e944a..c651c8d3a8 100644
>> --- a/fftools/ffmpeg.c
>> +++ b/fftools/ffmpeg.c
>> @@ -598,6 +598,7 @@ static void ffmpeg_cleanup(int ret)
>>          avsubtitle_free(&ist->prev_sub.subtitle);
>>          av_frame_free(&ist->sub2video.frame);
>>          av_freep(&ist->filters);
>> +        av_freep(&ist->decode_formats);
>>          av_freep(&ist->hwaccel_device);
>>          av_freep(&ist->dts_buffer);
>>
>> @@ -2800,6 +2801,15 @@ static enum AVPixelFormat
>> get_format(AVCodecContext *s, const enum AVPixelFormat
>>          const AVCodecHWConfig  *config = NULL;
>>          int i;
>>
>> +        if (ist->decode_formats) {
>> +            for (i = 0; ist->decode_formats[i] != AV_PIX_FMT_NONE; i++) {
>> +                if (ist->decode_formats[i] == *p)
>> +                    break;
>> +            }
>> +            if (ist->decode_formats[i] != *p)
>> +                continue;
>> +        }
>> +
>>          if (!(desc->flags & AV_PIX_FMT_FLAG_HWACCEL))
>>              break;
>>
>> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
>> index eb1eaf6363..b06fd18b1c 100644
>> --- a/fftools/ffmpeg.h
>> +++ b/fftools/ffmpeg.h
>> @@ -125,6 +125,8 @@ typedef struct OptionsContext {
>>      int        nb_ts_scale;
>>      SpecifierOpt *dump_attachment;
>>      int        nb_dump_attachment;
>> +    SpecifierOpt *decode_formats;
>> +    int        nb_decode_formats;
>>      SpecifierOpt *hwaccels;
>>      int        nb_hwaccels;
>>      SpecifierOpt *hwaccel_devices;
>> @@ -334,6 +336,8 @@ typedef struct InputStream {
>>      int top_field_first;
>>      int guess_layout_max;
>>
>> +    enum AVPixelFormat *decode_formats;
>> +
>>      int autorotate;
>>
>>      int fix_sub_duration;
>> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
>> index d4851a2cd8..63bb05053b 100644
>> --- a/fftools/ffmpeg_opt.c
>> +++ b/fftools/ffmpeg_opt.c
>> @@ -701,6 +701,7 @@ static void add_input_streams(OptionsContext *o,
>> AVFormatContext *ic)
>>          AVStream *st = ic->streams[i];
>>          AVCodecParameters *par = st->codecpar;
>>          InputStream *ist = av_mallocz(sizeof(*ist));
>> +        char *decode_formats = NULL;
>>          char *framerate = NULL, *hwaccel_device = NULL;
>>          const char *hwaccel = NULL;
>>          char *hwaccel_output_format = NULL;
>> @@ -797,6 +798,49 @@ static void add_input_streams(OptionsContext *o,
>> AVFormatContext *ic)
>>              ist->top_field_first = -1;
>>              MATCH_PER_STREAM_OPT(top_field_first, i, ist->top_field_first, ic,
>> st);
>>
>> +            MATCH_PER_STREAM_OPT(decode_formats, str, decode_formats, ic,
>> st);
>> +            if (decode_formats) {
>> +                const char *p, *q;
>> +                int i, nb_formats;
>> +                char tmp[32];
>> +
>> +                nb_formats = 0;
>> +                for (p = decode_formats; p; p = strchr(p + 1, ','))
>> +                    ++nb_formats;
>> +
>> +                ist->decode_formats =
>> +                    av_malloc_array(nb_formats + 1, sizeof(*ist->decode_formats));
>> +                if (!ist->decode_formats)
>> +                    exit_program(1);
>> +
>> +                p = decode_formats;
>> +                for (i = 0; i < nb_formats; i++) {
>> +                    q = strchr(p, ',');
>> +                    if (!q) {
>> +                        ist->decode_formats[i] = av_get_pix_fmt(p);
>> +                        if (ist->decode_formats[i] == AV_PIX_FMT_NONE)
>> +                            break;
>> +                        continue;
>> +                    }
>> +                    if (q - p > sizeof(tmp) - 1)
>> +                        break;
>> +                    memcpy(tmp, p, q - p);
>> +                    tmp[q - p] = 0;
>> +                    ist->decode_formats[i] = av_get_pix_fmt(tmp);
>> +                    if (ist->decode_formats[i] == AV_PIX_FMT_NONE)
>> +                        break;
>> +                    p = q + 1;
>> +                }
>> +                if (i < nb_formats) {
>> +                    av_log(NULL, AV_LOG_FATAL,
>> +                           "Unrecognised decode format: %s.\n", p);
>> +                    exit_program(1);
>> +                }
>> +                ist->decode_formats[nb_formats] = AV_PIX_FMT_NONE;
>> +            } else {
>> +                ist->decode_formats = NULL;
>> +            }
>> +
>>              MATCH_PER_STREAM_OPT(hwaccels, str, hwaccel, ic, st);
>>              if (hwaccel) {
>>                  // The NVDEC hwaccels use a CUDA device, so remap the name here.
>> @@ -3583,6 +3627,9 @@ const OptionDef options[] = {
>>          "audio bitrate (please use -b:a)", "bitrate" },
>>      { "b",            OPT_VIDEO | HAS_ARG | OPT_PERFILE | OPT_OUTPUT,
>> { .func_arg = opt_bitrate },
>>          "video bitrate (please use -b:v)", "bitrate" },
>> +    { "decode_format",  OPT_VIDEO | OPT_STRING | HAS_ARG |
>> OPT_EXPERT |
>> +                        OPT_SPEC | OPT_INPUT,                                    { .off =
>> OFFSET(decode_formats) },
>> +        "set output format(s) to be used by decoder, fail if none of these
>> formats are available", "format" },
>>      { "hwaccel",          OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT |
>>                            OPT_SPEC | OPT_INPUT,                                  { .off =
>> OFFSET(hwaccels) },
>>          "use HW accelerated decoding", "hwaccel name" },
>> --
>> 2.19.1
>>
> 
> Is there any other conditions which will cause the hwaccel failed and fallback to software path? 
> Like profile was not supported by hardware?

If this option is set then get_format will never choose a format not on the list you provide, so it shouldn't be able to use software decode unless a software format is on the list.

> I applied the patch and tested some cases, like yuv422  VAAPI decoding (currently not supported), HEVC decoding with unsupported profile.
> It reports an error like "hwaccel initialization returned error", and continue to decode and produce less frames than expected. (which I thought fallback still happened).

Can you give an example?  With -v debug there will be output saying exactly what happened in ff_get_format().

- Mark


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